CN111181396B - Suspension capacitance type multi-level bridge circuit and control method thereof - Google Patents

Suspension capacitance type multi-level bridge circuit and control method thereof Download PDF

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Publication number
CN111181396B
CN111181396B CN201911359302.7A CN201911359302A CN111181396B CN 111181396 B CN111181396 B CN 111181396B CN 201911359302 A CN201911359302 A CN 201911359302A CN 111181396 B CN111181396 B CN 111181396B
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capacitor
floating
charging unit
voltage
charging
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CN111181396A (en
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王腾飞
庄加才
杨宇
徐君
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Sungrow Power Supply Co Ltd
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Sungrow Power Supply Co Ltd
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
    • H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
    • H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/156—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators
    • H02M3/158—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators including plural semiconductor devices as final control devices for a single load
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/32—Means for protecting converters other than automatic disconnection
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
    • H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
    • H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/156—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators
    • H02M3/158—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators including plural semiconductor devices as final control devices for a single load
    • H02M3/1584—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators including plural semiconductor devices as final control devices for a single load with a plurality of power processing stages connected in parallel
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
    • H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
    • H02M3/06—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using resistors or capacitors, e.g. potential divider
    • H02M3/07—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using resistors or capacitors, e.g. potential divider using capacitors charged and discharged alternately by semiconductor devices with control electrode, e.g. charge pumps
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
    • H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
    • H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/156—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators
    • H02M3/158—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators including plural semiconductor devices as final control devices for a single load
    • H02M3/1584—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators including plural semiconductor devices as final control devices for a single load with a plurality of power processing stages connected in parallel
    • H02M3/1586—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators including plural semiconductor devices as final control devices for a single load with a plurality of power processing stages connected in parallel switched with a phase shift, i.e. interleaved

Abstract

The invention provides a suspension capacitance type multi-level bridge circuit and a control method thereof, wherein a three-level Buck circuit comprises: input capacitance, output capacitance and at least one bridge arm, the bridge arm includes: the device comprises a charging unit, a suspension capacitor, two inner pipes, two outer pipes and an inductor; the charging unit is connected in parallel with two ends of the outer tube which is not connected with the low-voltage side, when the three-level Buck circuit is connected with a power supply, most of the voltage which is originally added in the input voltage at the two ends of the outer tube is greatly reduced by dividing the voltage through the charging unit and the suspension capacitor, and therefore the outer tube is prevented from being damaged by overvoltage; simultaneously, carry out the precharge for the suspended capacitor through this charging unit, still can avoid leading to another outer tube overvoltage damage's problem because of switching on this outer tube and charge for the suspended capacitor to improve three level Buck circuit security.

Description

Suspension capacitance type multi-level bridge circuit and control method thereof
The present application claims priority of chinese patent application entitled "a three-level Buck circuit and control method thereof" filed by the chinese patent office on 11/09/2019 with application number 201910859287.6, the entire contents of which are incorporated herein by reference.
Technical Field
The invention belongs to the technical field of power electronics, and particularly relates to a suspension capacitance type multi-level bridge circuit and a control method thereof.
Background
With the rise of the system voltage of the power electronic converter, the voltage withstanding requirements of related switching devices are gradually raised, but due to the influence of semiconductor process performance and the like, the development of high-cost performance devices has certain hysteresis, and the related voltage withstanding requirements cannot be met in a short period of time, so that how to realize high-voltage power conversion by using lower-voltage-level devices and lower cost becomes a research hotspot, and the problem can be better solved by the proposal of the multilevel technology.
In the three-level Buck circuit shown in FIG. 1, the first outer tube K1 and the first inner tube K2 are alternately conducted in normal operation, and under ideal conditions, the conduction duty ratios of the first outer tube K1 and the first inner tube K2 are the same, so that the voltage stress of each switching tube is only half of the output voltage in normal operation. However, when the three-level Buck circuit is started, since the voltage Vf across the floating capacitor Cf is zero, if the input voltage Vin is greater than the withstand voltage of the first outer tube K1, the first outer tube K1 may be over-voltage broken; moreover, the first outer tube K1 is turned on to charge the floating capacitor, and then the voltage at the two ends of the first outer tube K1 is instantaneously transferred to the two ends of the second outer tube K4, so that the second outer tube K4 is damaged by overvoltage, therefore, the first outer tube K1 and the second outer tube K4 of the three-level Buck circuit are easily damaged by overvoltage, and further the three-level Buck circuit is failed.
Disclosure of Invention
In view of the above, an object of the present invention is to provide a floating capacitor type multi-level bridge circuit and a control method thereof, in which a first outer tube is prone to overvoltage breakdown during starting, resulting in failure of the first outer tube, and a second outer tube is prone to overvoltage breakdown failure due to conduction of the first outer tube for charging a floating capacitor, resulting in failure of a three-level Buck circuit.
The invention discloses a suspension capacitance type three-level Buck circuit in a first aspect, which comprises: an input capacitance, an output capacitance, and at least one leg, the leg comprising: the device comprises a charging unit, a suspension capacitor, two inner pipes, two outer pipes and an inductor; wherein:
two ends of the input capacitor are respectively used as the positive electrode and the negative electrode of the high-voltage side of the suspension capacitor type three-level Buck circuit;
two ends of the output capacitor are respectively used as the positive electrode and the negative electrode of the low-voltage side of the suspension capacitor type three-level Buck circuit;
in the bridge arm, the suspension capacitor is connected in parallel with the series branch of the two inner tubes, a connecting point between the two inner tubes is connected with one end of the inductor, the other end of the inductor is connected with one of the positive and negative electrodes of the low-voltage side, one outer tube is used for respectively connecting the other of the positive and negative electrodes of the low-voltage side and the corresponding one of the positive and negative electrodes of the high-voltage side, and the other outer tube is used for connecting the other of the positive and negative electrodes of the high-voltage side and is connected with the charging unit in parallel.
Optionally, the charging unit includes: a balancing capacitor and a charging diode connected in series;
if one end of the balance capacitor is connected with the anode of the charging diode, the other end of the balance capacitor is used as the input end of the charging unit, and the cathode of the charging diode is used as the output end of the charging unit;
and if one end of the balance capacitor is connected with the cathode of the charging diode, the other end of the balance capacitor is used as the output end of the charging unit, and the anode of the charging diode is used as the input end of the charging unit.
Optionally, the method further includes: and the discharging unit is used for discharging the balance capacitor after the suspension capacitance type three-level Buck circuit is powered down.
Optionally, the discharge unit includes: a discharge diode;
if the low-voltage side negative electrode of the suspension capacitance type three-level Buck circuit is connected with the high-voltage side negative electrode of the suspension capacitance type three-level Buck circuit, the anode of the discharge diode is connected with the low-voltage side negative electrode and the high-voltage side negative electrode, and the cathode of the discharge diode is connected with the charged negative electrode of the balance capacitor;
if the low-voltage-side positive electrode of the suspension capacitance type three-level Buck circuit is connected with the high-voltage-side positive electrode of the suspension capacitance type three-level Buck circuit, the cathode of the discharge diode is connected with the low-voltage-side positive electrode and the high-voltage-side positive electrode, and the anode of the discharge diode is connected with the charged positive electrode of the balance capacitor.
Optionally, when the floating capacitor type three-level Buck circuit is connected to a voltage source and is a stable input voltage source, between the stable input voltage source and the input capacitor, the method further includes: a current limiting unit;
and the current limiting unit is used for limiting the charging current of the parallel parasitic capacitor of the outer tube which is not connected with the charging unit when the suspension capacitance type three-level Buck circuit is connected to an input voltage source.
Optionally, the current limiting unit includes: the circuit comprises a first switch, a second switch and a current-limiting resistor;
the first switch is connected with the current-limiting resistor in series;
and the series branch of the first switch and the current-limiting resistor is connected with the second switch in parallel.
Optionally, the number of the bridge arms is n, and n is a positive integer greater than or equal to 2.
Optionally, the inner tube and the outer tube connected to the charging unit are respectively reverse conducting transistors, and are in a staggered conducting state during normal operation;
the inner tube and the outer tube which are not connected with the charging unit are respectively a diode or a reverse conducting transistor.
The invention discloses a control method of a floating capacitance type three-level Buck circuit, which is applied to a controller of the floating capacitance type three-level Buck circuit in any one of the first aspect, and the control method comprises the following steps:
controlling the suspension capacitance type three-level Buck circuit to be connected to an input voltage source;
and when the difference between the voltage of the floating capacitor and half of the input voltage is reduced to be smaller than a threshold value, controlling the inner tube and the outer tube which are connected with the charging unit in the floating capacitor type three-level Buck circuit to be conducted in a staggered mode.
Optionally, the controlling of the staggered conduction of the inner tube and the outer tube in the floating capacitance type three-level Buck circuit, which have a connection relationship with the charging unit, includes:
controlling an outer tube connected with the charging unit to be conducted and an inner tube connected with the charging unit to be switched off so as to charge a floating capacitor of the floating capacitor type three-level Buck circuit;
controlling the inner pipe and the outer pipe which are connected with the charging unit to be turned off, and charging the suspension capacitor and the charging unit;
controlling the outer pipe connected with the charging unit to be switched off and the inner pipe connected with the charging unit to be switched on to charge the charging unit;
and returning to the step of controlling the conduction of the outer pipe connected with the charging unit and the disconnection of the inner pipe connected with the charging unit until the voltage of the floating capacitor rises to be equal to half of the input voltage.
Optionally, the method further includes the following three steps executed in a cycle after the voltage of the floating capacitor rises to be equal to half of the input voltage:
controlling the conduction of an outer pipe connected with the charging unit and the disconnection of an inner pipe connected with the charging unit to charge the floating capacitor;
controlling the inner pipe and the outer pipe which are connected with the charging unit to be turned off, so that the suspension capacitor and the charging unit are not charged and discharged;
and controlling the outer pipe connected with the charging unit to be switched off and the inner pipe connected with the charging unit to be switched on so as to discharge the suspension capacitor.
Optionally, if the floating capacitive type three-level Buck circuit includes a current limiting unit, after the controlling the floating capacitive type three-level Buck circuit to access an input voltage source, the method further includes:
controlling a first switch of the current limiting unit to be closed;
and when the difference between the voltage of the floating capacitor and half of the input voltage is reduced to be smaller than a threshold value, a second switch of the current limiting unit is controlled to be closed, and then the step of controlling the inner tube and the outer tube which are connected with the charging unit in the floating capacitor type three-level Buck circuit to be conducted in a staggered mode is executed.
Optionally, if the inner tube and the outer tube that are not connected to the charging unit are reverse conducting transistors, the method further includes, while controlling the inner tube and the outer tube that are connected to the charging unit in the floating capacitive three-level Buck circuit to be alternately conducted:
and controlling two inner tubes and two outer tubes in the suspension capacitance type three-level Buck circuit to be in complementary conduction.
From the above technical solution, the floating capacitive three-level Buck circuit provided by the present invention is characterized by including: input capacitance, output capacitance and at least one bridge arm, the bridge arm includes: the device comprises a charging unit, a suspension capacitor, two inner pipes, two outer pipes and an inductor; wherein: the floating capacitor is connected with the series branch of the two inner tubes in parallel, a connecting point between the two inner tubes is connected with one end of an inductor, the other end of the inductor is connected with one of the positive and negative poles of the low-voltage side, the other end of an outer tube is connected with the other of the positive and negative poles of the low-voltage side and the one of the positive and negative poles of the high-voltage side, the other outer tube is used for connecting the other of the positive and negative poles of the high-voltage side and is connected with the charging unit in parallel, when the floating capacitor type three-level Buck circuit is connected with a power supply, most of input voltage which is originally applied to the two ends of the outer tube and is not connected with the low-voltage side is divided by the charging unit and the floating capacitor, so that the overvoltage damage of the outer tube is avoided; simultaneously, carry out the precharge for the suspended capacitor through the unit that charges, still can avoid leading to another outer tube overvoltage damage's problem because of switching on this outer tube and charge for the suspended capacitor to improve the three level Buck circuit security of suspended capacitor type.
A third aspect of the present invention discloses a floating capacitance type multilevel bridge circuit, including: the device comprises an input capacitor, an output circuit and at least one bridge arm; the bridge arm includes: the device comprises a suspension capacitance type n +1 level step-down conversion unit, a clamping circuit and n-1 charging units; n is a positive integer greater than 1; wherein:
the positive and negative electrodes of the input end of the suspension capacitance type n +1 level step-down conversion unit are used as the positive and negative electrodes of the input end of the bridge arm and are respectively connected with the two ends of the input capacitor;
the output end of the suspension capacitance type n +1 level buck conversion unit is used as one output end of the bridge arm and is connected with the first end of the output circuit;
the output end of each charging unit is respectively connected with the anode of the corresponding suspension capacitor in the suspension capacitor type n +1 level step-down conversion unit; the input end of each charging unit is respectively connected with any node of the upper bridge arm branch of the floating capacitive type n +1 level buck conversion unit, wherein the voltage of the node is higher than the voltage of a first preset connection point; the voltage of the first preset connection point is the voltage of the connection point of the anode of the corresponding suspension capacitor and the corresponding power tube; alternatively, the first and second electrodes may be,
the input end of each charging unit is respectively connected with the negative electrode of the corresponding suspension capacitor in the suspension capacitor type n +1 level step-down conversion unit; the output end of each charging unit is respectively connected with any node, of which the voltage in the lower bridge arm branch of the suspended capacitive type n +1 level buck conversion unit is lower than the voltage of a second preset connection point; and the voltage of the second preset connection point is the voltage of the connection point of the negative electrode of the corresponding suspension capacitor and the corresponding power tube.
Optionally, each of the charging units includes: a balancing capacitor and a charging diode connected in series;
the negative electrode of the balance capacitor is connected with the anode of the charging diode, the positive electrode of the balance capacitor is used as the input end of the charging unit, and the cathode of the charging diode is used as the output end of the charging unit;
alternatively, the first and second electrodes may be,
the anode of the balance capacitor is connected with the cathode of the charging diode, the anode of the charging diode is used as the input end of the charging unit, and the cathode of the balance capacitor is used as the output end of the charging unit.
Optionally, the method further includes: a clamp circuit;
the input end of the clamping circuit is connected with the midpoint of the suspended capacitive type n +1 level step-down conversion unit, and the output end of the clamping circuit is connected with the negative electrode of the input end of the suspended capacitive type n +1 level step-down conversion unit;
the clamping circuit maintains the off state when the suspension capacitance type multi-level bridge circuit is in a normal working state, and maintains the on state at other time.
Optionally, the clamping circuit includes: a clamp capacitor and a third switch connected in series;
the positive electrode of the clamping capacitor is connected with one end of the third switch, the other end of the third switch is used as the input end of the clamping circuit, and the negative electrode of the clamping capacitor is used as the output end of the clamping circuit;
alternatively, the first and second electrodes may be,
the negative electrode of the clamping capacitor is connected with one end of the third switch, the positive electrode of the clamping capacitor is used as the input end of the clamping circuit, and the other end of the third switch is used as the output end of the clamping circuit.
Optionally, the capacitance value of the clamp capacitor is greater than the capacitance values of the respective floating capacitors and the respective balance capacitors, and the difference between the capacitance value of the clamp capacitor and the capacitance values of the respective floating capacitors and the respective balance capacitors is greater than a preset capacitance value.
Optionally, the third switch is any one of a relay, an IGBT (Insulated Gate bipolar Transistor) and a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor).
Optionally, when the floating capacitive multilevel bridge circuit is applied to a multilevel Buck circuit:
if each charging unit is connected with the anode of the corresponding floating capacitor, the second end of the output circuit is connected with the cathode of the input end of the floating capacitor type n +1 level step-down conversion unit;
and if each charging unit is respectively connected with the negative electrode of the corresponding suspension capacitor, the second end of the output circuit is connected with the positive electrode of the input end of the suspension capacitor type n +1 level step-down conversion unit.
Optionally, the floating capacitive type n +1 level buck conversion unit includes: the device comprises an inductor, an upper bridge arm branch, a lower bridge arm branch and n-1 suspension capacitors; wherein:
the upper bridge arm branch and the lower bridge arm branch respectively comprise n power tubes which are sequentially connected in series, and a connection point between every two power tubes is used as a node; the upper bridge arm branch is connected with the lower bridge arm branch, and a connection point is used as a midpoint of the suspension capacitance type n +1 level buck conversion unit;
one end of the inductor is connected with the midpoint, and the other end of the inductor is used as the output end of the suspended capacitive type n +1 level step-down conversion unit;
one end of each suspension capacitor is connected with each node in the upper bridge arm branch in a one-to-one correspondence mode, and the other end of each suspension capacitor is connected with the symmetrical nodes in the lower bridge arm branch in a one-to-one correspondence mode.
Optionally, the bridge arm further includes: the n-1 discharge units are used for discharging corresponding balance capacitors after the suspension capacitance type multi-level bridge circuit is powered down;
and/or the presence of a gas in the gas,
when the input voltage source accessed by the suspension capacitance type multilevel bridge circuit is a stable input voltage source, the bridge arm further comprises: and the current limiting unit is arranged between the stable input voltage source and the input capacitor and used for limiting the charging current of the parallel parasitic capacitor of the power tube which is not connected with the charging unit and the midpoint when the suspended capacitive multi-level bridge circuit is connected to the input voltage source.
Optionally, each of the discharge units includes: a discharge diode;
if at least one charging unit is connected with the anode of the input capacitor, the anode of the discharging diode is respectively connected with the cathode of the input capacitor and the cathode of the input end of the bridge arm, and the cathode of the discharging diode is connected with the cathode of the corresponding balance capacitor;
if at least one charging unit is connected with the negative electrode of the input capacitor, the cathode of the discharging diode is respectively connected with the positive electrode of the input capacitor and the positive electrode of the input end of the bridge arm, and the anode of the discharging diode is connected with the positive electrode of the corresponding balance capacitor;
the current limiting unit includes: the circuit comprises a first switch, a second switch and a current-limiting resistor; the first switch is connected with the current-limiting resistor in series, and a series branch of the first switch and the current-limiting resistor is connected with the second switch in parallel.
Optionally, each power tube in the upper bridge arm branch is a diode or a reverse conducting transistor;
each power tube in the lower bridge arm branch is a diode or a reverse conducting transistor; each power tube in the upper bridge arm branch and each power tube in the lower bridge arm branch are not diodes at the same time;
if each power tube in the lower bridge arm branch is a diode, each charging unit is connected with the anode of the corresponding suspension capacitor;
and if each power tube in the upper bridge arm branch is a diode, each charging unit is connected with the cathode of the corresponding suspension capacitor.
Optionally, before the floating capacitive multilevel bridge circuit enters a normal operating state after being powered on, each charging unit is in a conducting state, so that the voltage on the corresponding floating capacitor is charged to a preset range of a steady-state voltage corresponding to the floating capacitive multilevel bridge circuit after entering the normal operating state through each charging unit.
The fourth aspect of the present invention discloses a control method for a floating capacitive multilevel bridge circuit, which is applied to a controller for a floating capacitive multilevel bridge circuit according to the third aspect of the present invention, and the control method includes:
controlling the suspension capacitance type multi-level bridge circuit to be connected to an input voltage source;
and when the difference value between the voltage of each floating capacitor and the corresponding steady-state voltage of the floating capacitor type multi-level bridge circuit after the floating capacitor type multi-level bridge circuit enters a normal working state is reduced to be smaller than a threshold value, controlling two adjacent power tubes in the floating capacitor type multi-level bridge circuit, which are connected with the charging unit, to be in staggered conduction.
Optionally, controlling two adjacent power transistors in the floating capacitive multi-level bridge circuit, which are connected to the charging unit, to be alternately turned on includes:
controlling power tubes which are connected with the charging units and are positioned at odd-numbered positions to be conducted, and controlling power tubes which are connected with the charging units and are positioned at even-numbered positions to be disconnected, and charging corresponding floating capacitors and corresponding charging units in the floating capacitor type multi-level bridge circuit;
controlling each power tube connected with the charging unit to be turned off, and charging each suspension capacitor and each charging unit;
controlling the power tubes which are connected with the charging unit and are positioned at odd numbers to be switched off, and controlling the power tubes which are connected with the charging unit and are positioned at even numbers to be switched on, so as to charge the corresponding charging unit and the corresponding floating capacitor;
and returning to the step of controlling the conduction of the power tube which is in the odd number and is connected with each charging unit and the disconnection of the power tube which is in the even number and is connected with the charging unit, and charging the corresponding floating capacitor and the corresponding charging unit in the floating capacitor type multi-level bridge circuit until the voltage of each floating capacitor rises to be equal to the corresponding steady-state voltage.
Optionally, the method further includes the following three steps executed in a cycle after the voltage of each floating capacitor rises to be equal to the corresponding steady-state voltage:
controlling the power tubes which are connected with the charging unit and are positioned at odd numbers to be conducted, and controlling the power tubes which are connected with the charging unit and are positioned at even numbers to be disconnected, so as to charge the corresponding floating capacitors;
controlling each power tube connected with the charging unit to be turned off, so that each suspension capacitor and each charging unit are not charged or discharged;
and controlling the power tube which is connected with the charging unit and is positioned at an odd number position to be switched off, and controlling the power tube which is connected with the charging unit and is positioned at an even number position to be switched on, so as to discharge the corresponding suspension capacitor.
Optionally, if the floating capacitive multilevel bridge circuit includes a current limiting unit, after the controlling the floating capacitive multilevel bridge circuit to access an input voltage source, the method further includes:
controlling a first switch of the current limiting unit to be closed;
and when the difference value between the voltage of each floating capacitor and the corresponding steady-state voltage is reduced to be less than the threshold value, the second switch of the current limiting unit is controlled to be closed, and then the step of controlling the two adjacent power tubes in the floating capacitor type multi-level bridge circuit, which are connected with the charging unit, to be conducted in a staggered mode is executed.
Optionally, if each power transistor in the floating capacitive type multilevel bridge circuit that is not connected to the charging unit is a field effect transistor MOS transistor, the method further includes, while controlling that two adjacent power transistors in the floating capacitive type multilevel bridge circuit that are connected to the charging unit are alternately turned on:
controlling each power tube in the suspension capacitance type multi-level bridge circuit, which is not connected with the charging unit, to be in complementary conduction with the symmetrical power tube connected with the charging unit; or controlling each power tube which is not connected with the charging unit in the floating capacitance type multi-level bridge circuit to keep an off state.
From the above technical solution, the present invention provides a three-level Buck circuit, including: input capacitance, output capacitance and at least one bridge arm, the bridge arm includes: the device comprises a charging unit, a suspension capacitor, two inner pipes, two outer pipes and an inductor; wherein: the three-level Buck circuit is connected with a power supply, most of input voltage which is originally applied to two ends of the outer tube which is not connected with the low-voltage side is divided into partial voltage by the charging unit and the suspension capacitor, so that the outer tube is prevented from being damaged by overvoltage; simultaneously, carry out the precharge for the suspension capacitor through the unit that charges, still can avoid leading to another outer tube overvoltage damage's problem because of switching on this outer tube and charge for the suspension capacitor to improve three level Buck circuit security.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.
FIG. 1 is a schematic diagram of a three-level Buck circuit provided in the prior art;
FIG. 2 is a timing diagram illustrating the conduction of a first outer tube and a first inner tube in a three-level Buck circuit provided by the prior art;
FIGS. 3-12 are schematic diagrams of a floating capacitor type three-level Buck circuit according to an embodiment of the present invention;
fig. 13-14 are flowcharts illustrating a control method of a floating capacitive three-level Buck circuit according to an embodiment of the present invention;
FIG. 15 is a schematic diagram of another three-level Buck circuit provided by the prior art;
FIG. 16 is a schematic diagram of a conventional floating capacitor type n +1 level bridge circuit provided in the prior art;
FIGS. 17-22 are schematic diagrams of a floating capacitance multi-level bridge circuit according to embodiments of the present invention;
fig. 23 to 24 are flowcharts illustrating a control method of a floating capacitive multilevel bridge circuit according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In this application, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.
It should be noted that, in the three-level Buck circuit shown in fig. 1, during normal operation, the first outer tube K1 and the first inner tube K2 are alternately turned on. Under ideal working conditions, the conduction duty cycles of the first outer tube K1 and the first inner tube K2 are the same and are both D, and the conduction timing diagram is shown in fig. 2, then:
the output voltage Vout and the input voltage Vin satisfy: vout ═ D × Vin.
The voltage across the floating capacitor Cf is:
Figure BDA0002336739540000111
the voltage stress of each switching tube is as follows:
Figure BDA0002336739540000112
Figure BDA0002336739540000113
Figure BDA0002336739540000114
Figure BDA0002336739540000115
vf is a voltage of the floating capacitor Cf, Vk1 is a voltage stress of the first outer tube K1, Vk2 is a voltage stress of the first inner tube K2, Vk3 is a voltage stress of the second inner tube K3, and Vk4 is a voltage stress of the second outer tube K4.
From the above equations, it can be seen that the voltage stress of each switching tube is only half of the input voltage during normal operation. However, when the three-level Buck circuit is started, since the voltage Vf between the two ends of the floating capacitor Cf is zero, the difference between the withstand voltage of each switching tube and the steady-state operating time is large, which is:
Vk1＝Vin-Vf＝Vin
Vk2＝Vf＝0
Vk3＝0
Vk4＝0
at this time, if the input voltage Vin is greater than the withstand voltage of the first outer tube K1, the first outer tube K1 will fail due to overvoltage breakdown, and the three-level Buck circuit will fail.
Therefore, the embodiment of the invention discloses a suspension capacitor type three-level Buck circuit, which aims to solve the problem that the first outer tube K1 fails due to the fact that the first outer tube K1 is prone to overvoltage breakdown when being started, and further the suspension capacitor type three-level Buck circuit fails.
The floating capacitance type three-level Buck circuit, as shown in FIG. 3 or FIG. 4, includes: input capacitance Cin, output capacitance Co and at least one bridge arm 310, bridge arm 310 includes: the charging unit 311, the floating capacitor Cf, two inner tubes (a first inner tube K2 and a second inner tube K3), two outer tubes (a first outer tube K1 and a second outer tube K4), and an inductor L; wherein:
two ends of the input capacitor Cin are respectively used as the positive electrode and the negative electrode of the high-voltage side of the suspension capacitor type three-level Buck circuit. Two ends of the output capacitor Co are respectively used as the positive electrode and the negative electrode of the low-voltage side of the suspension capacitance type three-level Buck circuit. In bridge arm 310, charging unit 311 is connected in parallel to first outer tube K1. The suspension capacitor Cf is connected with a series branch of the two inner tubes (the first inner tube K2 and the second inner tube K3) in parallel, a connecting point between the two inner tubes (the first inner tube K2 and the second inner tube K3) is connected with one end of an inductor L, and the other end of the inductor L is connected with one of the positive pole and the negative pole of the low-voltage side. The second outer tube K4 is used to connect the other of the low-voltage side positive and negative electrodes and the one of the high-voltage side positive and negative electrodes with the same polarity. The first outer tube K1 is used to connect the other of the high-voltage-side positive and negative electrodes, and is connected in parallel with the charging unit 311.
Specifically, referring to fig. 3 as an example, the first outer tube K1, the first inner tube K2, the second inner tube K3, and the second outer tube K4 are connected in series. One end of an input capacitor Cin connected with the first outer tube K1 is used as a high-voltage side anode of the suspension capacitor type three-level Buck circuit, and one end of the input capacitor Cin connected with the second outer tube K4 is used as a high-voltage side cathode of the suspension capacitor type three-level Buck circuit. One end of the output capacitor Co connected with the inductor L is used as the low-voltage side anode of the suspension capacitor type three-level Buck circuit, and the other end of the output capacitor Co connected with the second outer tube K4 is used as the low-voltage side cathode of the suspension capacitor type three-level Buck circuit. The charging unit 311 is connected in parallel to the first outer tube K1. One end of the floating capacitor Cf is connected with the connection point of the first outer tube K1 and the first inner tube K2, and the other end of the floating capacitor Cf is connected with the connection point of the second inner tube K3 and the second outer tube K4. The other end of the inductance L is connected with the connection point of the first inner tube K2 and the second inner tube K3.
More specifically, one end of the input capacitor Cin is connected to one end of the charging unit 311 and one end of the first outer tube K1, respectively, and the connection point is used as a high-voltage side positive electrode, the other end of the input capacitor Cin is connected to one end of the second outer tube K4 and a low-voltage side negative electrode, respectively, and the connection point is used as a high-voltage side negative electrode.
The other end of the first outer tube K1 is connected to the other end of the charging unit 311, one end of the first inner tube K2 and one end of the floating capacitor Cf, respectively; the other end of the first inner tube K2 is respectively connected with one end of the second inner tube K3 and one end of an inductor L, the other end of the inductor L is connected with one end of an output capacitor Co, the connection point is used as a low-voltage side anode, and the other end of the output capacitor Co is used as a low-voltage side cathode.
The other end of the second inner tube K3 is connected to the other end of the floating capacitor Cf and the other end of the second outer tube K4, respectively.
Referring to fig. 4, the circuit shown in fig. 4 is a dual circuit with the circuit shown in fig. 3, and the connection relationship of each device in the circuit shown in fig. 4 is similar to that of each device in the circuit shown in fig. 3, which can be referred to the description of the drawing in fig. 3 and is not repeated herein; the difference is that one end of the input capacitor Cin is connected to one end of the charging unit 311 and one end of the first outer tube K1, the connection point is used as a high-voltage side cathode, the other end of the input capacitor Cin is connected to one end of the second outer tube K4 and a low-voltage side anode, the connection point is used as a high-voltage side anode, one end of the inductor L is connected to the output capacitor Co, the connection point is used as a high-voltage side cathode, and the other end of the output capacitor Co is used as a low-voltage side anode.
In practical applications, the first inner tube K2 and the first outer tube K1 connected to the charging unit 311 are reverse conducting transistors respectively, and are in a staggered conducting state during normal operation; the second inner tube K3 and the second outer tube K4, which are not connected to the charging unit 311, are diodes or transistors of a reverse conducting type, respectively.
In this embodiment, when the floating capacitive three-level Buck circuit is powered on, most of the input voltages originally applied to the two ends of the first outer tube K1 are greatly reduced in voltage by dividing the voltage through the charging unit 311 and the floating capacitor Cf, so as to avoid the overvoltage damage to the first outer tube K1; meanwhile, the floating capacitor Cf is precharged through the charging unit 311, and the problem that the second outer tube K4 is damaged due to overvoltage caused by conducting the first outer tube K1 to charge the floating capacitor Cf can be solved, so that the safety of the floating capacitor type three-level Buck circuit is improved, the restrictive condition of the floating capacitor type three-level Buck circuit in actual use is smaller, and the advantages of the floating capacitor type three-level Buck circuit are fully exerted.
It should be noted that, as shown in fig. 15, in the prior art, the precharge circuit 10 is provided at both ends of the floating capacitor Cf. In the floating capacitor type three-level Buck circuit, before an input voltage source is connected to the floating capacitor type three-level Buck circuit, the pre-charging circuit 10 charges the floating capacitor Cf, and when the voltage of the floating capacitor Cf is reduced, the pre-charging circuit 10 needs to charge the floating capacitor Cf again to ensure that the floating capacitor Cf is reserved with corresponding voltage in advance, so that overvoltage damage to the first outer tube K1 is avoided. Specifically, an additional branch is needed to provide power for the pre-charge circuit 10, so as to pre-charge the floating capacitor Cf by the pre-charge circuit 10. Before the input end of the floating capacitor type three-level Buck circuit is connected to an input voltage source, the floating capacitor type three-level Buck circuit needs to be controlled to start working, that is, the pre-charging circuit 10 is controlled to charge the floating capacitor Cf, so that the operation is very inconvenient.
In the embodiment, an additional branch circuit is not needed, and the floating capacitive type three-level Buck circuit is not needed to be controlled to start working before the floating capacitive type three-level Buck circuit is connected to a power supply, so that the operation is very convenient.
Optionally, the charging unit 311 referred to in fig. 3 or fig. 4 in the embodiment of the present invention, referring to fig. 5 to 8, may include: a balancing capacitor C1 and a charging diode D1 connected in series.
Referring to fig. 6 or 7, one end of the balancing capacitor C1 is connected to the anode of the charging diode D1, the other end of the balancing capacitor C1 serves as the input terminal of the charging unit 311, and the cathode of the charging diode D1 serves as the output terminal of the charging unit 311.
Specifically, referring to fig. 6, one end of a balance capacitor C1 is connected to the anode of the charging diode D1, the other end of the balance capacitor C1 is connected to the high-voltage-side anode and one end of the first outer tube K1, respectively, and the cathode of the charging diode D1 is connected to the other end of the first outer tube K1, one end of the floating capacitor Cf, and one end of the first inner tube K2, respectively; at this time, one end of the balance capacitor C1 connected to the high-voltage side positive electrode serves as an input end of the charging unit 311, and the cathode of the charging diode D1 serves as an output end of the charging unit 311.
Referring to fig. 7, one end of a balance capacitor C1 is connected to the anode of the charging diode D1, the other end of the balance capacitor C1 is connected to one end of the first outer tube K1, one end of the floating capacitor Cf, and one end of the first inner tube K2, respectively, the cathode of the charging diode D1 is connected to the high-voltage negative electrode and the other end of the first outer tube K1, at this time, one end of the balance capacitor C1 connected to the floating capacitor Cf serves as the input end of the charging unit 311, and the cathode of the charging diode D1 serves as the output end of the charging unit 311.
Referring to fig. 5 or 8, one end of the balancing capacitor C1 is connected to the cathode of the charging diode D1, the other end of the balancing capacitor C1 is the output terminal of the charging unit 311, and the anode of the charging diode D1 is the input terminal of the charging unit 311.
Specifically, referring to fig. 5, one end of a balance capacitor C1 is connected to the cathode of the charging diode D1, the other end of the balance capacitor C1 is connected to one end of the first outer tube K1, one end of the first inner tube K2 and one end of the floating capacitor Cf, respectively, and the anode of the charging diode D1 is connected to the high-voltage-side anode and the other end of the first outer tube K1, respectively; at this time, the anode of the charging diode D1 is used as the input terminal of the charging unit 311, and the end of the balance capacitor C1 connected to the floating capacitor Cf is used as the output terminal of the charging unit 311.
Referring to fig. 8, one end of a balance capacitor C1 is connected to the cathode of the charging diode D1, the other end of the balance capacitor C1 is connected to the high-voltage side negative electrode and one end of the first outer tube K1, respectively, and the anode of the charging diode D1 is connected to the other end of the first outer tube K1, one end of the first inner tube K2, and one end of the floating capacitor Cf, respectively; at this time, the anode of the charging diode D1 is used as the input terminal of the charging unit 311, and the terminal of the balance capacitor C1 connected to the high-voltage side cathode is used as the output terminal of the charging unit 311.
In the embodiment, the floating capacitor Cf is charged through the balancing capacitor C1 and the charging diode D1 which are connected in series, so that the problems that the voltage stress of the first outer tube K1 is too high when the first outer tube K is started and the floating capacitor Cf is pre-charged to cause overvoltage damage are solved; and under the condition of not increasing the circuit loss, the number of sampling paths and the control complexity, the charging speed of the floating capacitor Cf is increased, and the dynamic response of the circuit is improved.
It should be noted that, in the above embodiments of fig. 5-8, the balancing capacitor C1 cannot be discharged after being powered down, and based on the implementation of fig. 5 or 7, see fig. 9 (shown on the basis of fig. 5) or fig. 10 (shown on the basis of fig. 7), the method may further include: and a discharge unit 312.
And the discharge unit 312 is used for discharging the balance capacitor C1 after the floating capacitance type three-level Buck circuit is powered down.
In practical applications, the discharge unit 312 may include: a discharge diode Dd.
Referring to fig. 9, the low-voltage side negative electrode of the floating capacitive type three-level Buck circuit is connected to the high-voltage side negative electrode of the floating capacitive type three-level Buck circuit, the anode of the discharge diode Dd is connected to the low-voltage side negative electrode and the high-voltage side negative electrode, the cathode of the discharge diode Dd is connected to the charged negative electrode of the balancing capacitor C1, that is, the cathode of the discharge diode Dd is connected to the connection point of the balancing capacitor C1 and the charging diode D1, and the cathode of the charging diode D1 is connected to one end of the first outer tube K1, one end of the floating capacitor Cf, and one end of the first inner tube K2, respectively.
After the floating capacitive type three-level Buck circuit is powered on, the discharge diode Dd is cut off, after the floating capacitive type three-level Buck circuit is powered off, the discharge diode Dd is turned on, and the discharge diode Dd discharges for the balance capacitor C1.
Referring to fig. 10, the low-voltage side positive electrode of the floating capacitance type three-level Buck circuit is connected to the high-voltage side positive electrode of the floating capacitance type three-level Buck circuit, the cathode of the discharge diode Dd is connected to the low-voltage side positive electrode and the high-voltage side positive electrode, the anode of the discharge diode Dd is connected to the charged positive electrode of the balancing capacitor C1, that is, the anode of the discharge diode Dd is connected to the connection point of the balancing capacitor C1 and the charging diode D1, and the anode of the charging diode D1 is connected to one end of the first outer tube K1, one end of the floating capacitor Cf, and one end of the first inner tube K2, respectively.
After the floating capacitive three-level Buck circuit is powered on, the discharge diode Dd is cut off, and when the floating capacitive three-level Buck circuit is powered off, the discharge diode Dd is turned on, and the discharge diode Dd discharges for the balance capacitor C1.
After the balance capacitor C1 is charged, the two ends of the balance capacitor C1 are respectively used as the positive electrode and the negative electrode, the end closer to the positive electrode on the high-voltage side is used as the positive electrode, and the end closer to the negative electrode on the high-voltage side is used as the negative electrode.
In this embodiment, after the floating capacitive type three-level Buck circuit is powered down, the discharge unit 312 discharges the balance capacitor C1 quickly, so that the problem that potential safety hazards exist during maintenance due to the fact that the balance capacitor C1 in the floating capacitive type three-level Buck circuit is electrified for a long time is solved.
Optionally, on the basis of any one of fig. 3 to 10, referring to fig. 11 (which is shown as an example on the basis of fig. 9), when the input voltage source connected to the floating capacitive type three-level Buck circuit is a stable input voltage source DC, between the stable input voltage source DC and the input capacitor Cin, the method may further include: a current limiting unit 313.
And the current limiting unit 313 is used for limiting the charging current of the parallel parasitic capacitor of the outer tube (namely the second outer tube K4) which is not connected with the charging unit when the floating capacitive type three-level Buck circuit is connected with the input voltage source DC.
In practical applications, the current limiting unit 313 includes: a first switch S1, a second switch S2, and a current limiting resistor R.
The first switch S1 is connected in series with the current limiting resistor R, and the series branch of the first switch S1 and the current limiting resistor R is connected in parallel with the second switch S2.
The reason why the current limiting resistor R is connected between the stable input voltage source DC and the input capacitor Cin is that when the stable input voltage source DC is a voltage source with a capacitor, and when the initial voltage of the stable input voltage source DC is very high, such as 1500V, at this time, if the current limiting resistor R is not provided, at the moment that the suspension capacitor type three-level Buck circuit is connected to the input voltage source, the capacitor of the stable input voltage source DC charges the balance capacitor C1, the suspension capacitor Cf and the parasitic capacitors at the two ends of the second outer tube K4 by using a maximum charging current, and since the capacitance values of the balance capacitor C1 and the suspension capacitor Cf are far larger than the parasitic capacitors at the two ends of the second outer tube K4, according to the capacitance voltage division principle, the smaller the capacitance value is, and the voltage division is higher; therefore, the main voltage of the stabilized input voltage source DC is applied across the second external tube K4, causing it to be damaged by overvoltage.
If the current-limiting resistor R is arranged, the charging current of the second outer tube K4 is reduced, the second outer tube K4 and a second inner tube K3-inductor L-output capacitor Co loop are in a parallel connection relationship, the capacitance of the output capacitor Co is extremely large and is generally far larger than the capacitance of the balance capacitor C1 and the capacitance of the suspension capacitor Cf, the voltage at two ends of the second outer tube K4 is restrained from being rapidly increased, and the second outer tube K4 is guaranteed against overvoltage damage. For the floating capacitive type three-level Buck circuit, which is connected to the input voltage source and is a photovoltaic input voltage source, the current limiting unit 313 may be omitted, and the current limiting unit 313 may also be omitted for other floating capacitive type three-level Buck circuits with input voltage sources having limited output current or slowly increasing output voltage.
The circuit added with the current limiting unit 313 in fig. 3-8 and 10 is similar to the circuit shown in fig. 11, and is not described again here, and is within the scope of the present application.
It should be noted that any one or more of the above circuits may be selected to be used in combination according to the application environment and the user's requirements, and certainly not limited to the above exemplary circuits, other circuits that can pre-charge the floating capacitor Cf to avoid the overvoltage damage of the first outer tube K1 can be implemented, and are within the scope of the present application.
Optionally, in the embodiments of fig. 3 to 12 of the present invention, referring to fig. 12 (which is shown by taking fig. 5 as an example), the number of the bridge arms 310 is n, and n is a positive integer greater than or equal to 2, such as 3.
The n bridge arms 310 are connected in parallel, the n bridge arms 310 share an input capacitor Cin and an output capacitor Co, and the suspension capacitance type three-level Buck circuit can be used for a parallel connection staggered system; compared with a topology with different input and output grounds, the n-path parallel topology is more easily applied to a multi-path interleaving parallel system, the number of the inductors L is reduced, and meanwhile, the size and the cost of the inductors L can be saved.
Because one of the input end and the output end of the suspension capacitance type three-level Buck circuit is directly electrically connected, the n bridge arms 310 are independent from each other, and the phase shift is driven by corresponding switching tubes (namely a first outer tube K1, a first inner tube K2, a second inner tube K3 and a second outer tube K4) among the n bridge arms 310, so that the staggered parallel connection can be realized.
In the embodiment, the bridge arms 310 are ensured to be independent and not coupled, the advantage of the frequency multiplication of the suspension capacitance type three-level Buck circuit for reducing the L-inductance value of the output inductor is fully utilized, and the staggered parallel structure reduces the input and output current ripples, so that the current stress of the input capacitor Cin and the output capacitor Co is reduced, the cost is further saved, and the power density is improved.
The invention discloses a control method of a suspension capacitor type three-level Buck circuit, which is applied to a controller of the suspension capacitor type three-level Buck circuit, wherein the suspension capacitor type three-level Buck circuit is the suspension capacitor type three-level Buck circuit described in any one of the embodiments of figures 1-12. Referring to fig. 13, the control method includes:
s301, controlling the floating capacitive type three-level Buck circuit to be connected to an input voltage source;
in an initial situation, that is, before the input voltage source is connected, the voltage of each device in the floating capacitance type three-level Buck circuit is 0, when the input voltage source is connected to the floating capacitance type three-level Buck circuit, the floating capacitance type three-level Buck circuit is still in a standby state, the voltage of the input capacitor Cin is rapidly charged to the voltage of the input voltage source, and the input voltage source charges the floating capacitor Cf through the charging unit 311.
For convenience of explanation, the setting of each capacitance value in the floating capacitance type three-level Buck circuit may be C1 ═ Cf, Co > > C1; wherein, C1 is the capacitance of the balance capacitance C1, Cf is the capacitance of the floating capacitance Cf, and Co is the capacitance of the output capacitance Co; in addition, the parasitic capacitance of the first outer tube K1, the first inner tube K2, the second inner tube K3 and the second outer tube K4 is much smaller than that of the balance capacitor C1, and the maximum input voltage may be 1500V; of course, the values of the capacitance and the maximum input voltage of each device of the floating capacitance type three-level Buck circuit can be other values, and the values are determined according to actual requirements and are within the protection range of the application.
After the input voltage source is connected, the voltage of the charging unit 311 is equal to the voltage of the floating capacitor Cf; at this time, the parasitic capacitance of the second outer tube K4 is in parallel with the branch of the anti-parallel diode, the inductor L, and the output capacitor Co of the second inner tube K3. Because the output capacitor Co exists and the capacitance thereof is much larger than that of the charging unit 311, according to the capacitance voltage division principle, the voltage difference between the common terminal of the second inner tube K3 and the second outer tube K4 and the negative electrode of the input voltage source is zero; therefore, the input voltage is mainly applied to the charging unit 311 and the floating capacitor Cf, that is, the voltages of the charging unit 311 and the floating capacitor Cf are equal to and approximately equal to one half of the input voltage, the voltage across the first outer tube K1 is clamped by the charging unit 311, and the voltage of the first outer tube K1 is equal to the voltage of the charging unit 311 and approximately equal to one half of the input voltage, so that the first outer tube K1 is not damaged by over voltage.
In fact, the output capacitor Co cannot be infinite, so that after the input voltage source is connected, there will be a small voltage on the output capacitor Co, resulting in the voltages on the charging unit 311 and the floating capacitor Cf being slightly lower than Vin/2. The floating capacitive three-level Buck circuit enters an operation mode to charge the charging unit 311 and the floating capacitor Cf, and the specific implementation and principle are described below.
It should be noted that before the floating capacitance type three-level Buck circuit is connected to the input voltage source, both the inner tube and the outer tube in the floating capacitance type three-level Buck circuit are in an off state, and then before the difference between the voltage of the floating capacitance Cf and half of the input voltage is reduced to be smaller than the threshold value, both the inner tube and the outer tube in the floating capacitance type three-level Buck circuit are kept in the off state, that is, before the difference between the voltage of the floating capacitance Cf and half of the input voltage is reduced to be smaller than the threshold value, both the inner tube and the outer tube are kept in the off state, and whether the difference between the voltage of the floating capacitance Cf and half of the input voltage is reduced to be smaller than the threshold value is continuously judged.
In practical applications, if the floating capacitive three-level Buck circuit includes the current limiting unit 313, after step S301, the method may further include:
the first switch S1 of the current limiting unit 313 is controlled to be closed, so that the current limiting resistor R is connected between the regulated input voltage source DC and the input capacitor Cin, and the charging current of the second outer tube K4 is further reduced.
When the difference between the voltage of the floating capacitor Cf and half of the input voltage is decreased to be less than the threshold, the second switch S2 of the current limiting unit 313 is first controlled to be closed, so that the current limiting resistor R is separated from the voltage-stabilizing input voltage source DC and the input capacitor Cin, and power loss caused by the current limiting resistor R is avoided, and then step S302 is executed.
And S302, when the difference value between the voltage of the floating capacitor and half of the input voltage is reduced to be smaller than a threshold value, controlling the inner tube and the outer tube which are connected with the charging unit in the floating capacitor type three-level Buck circuit to be conducted in a staggered mode.
The floating capacitor and the charging unit are the floating capacitor Cf and the charging unit 31 shown in the above-described embodiment. In one switching period, the conduction duty ratios of the inner tube and the outer tube connected to the charging unit 311 may be equal or unequal, depending on the specific application environment, and are all within the protection scope of the present application.
Specifically, the inner tube connected to the charging unit 311 is the first inner tube K2, and the outer tube connected to the charging unit 311 is the first outer tube K1, that is, the first outer tube K1 and the first inner tube K2 are alternately turned on, assuming that the turn-on duty ratios of the first outer tube K1 and the first inner tube K2 are the same and are D, and 0< D <0.5, the turn-on timing charts of the first outer tube K1 and the first inner tube K2 are shown in fig. 2: dividing a switching period T into three parts, such as a first part with 0< T < D T, a second part with D T < 0.5T and 0.5T + D T < T, and a third part with 0.5T < 0.5T + D T; the first outer pipe K1 and the first inner pipe K2 are communicated in a staggered mode in the three parts.
In practical applications, referring to fig. 14, step S302 may include three steps S401 to S403.
For convenience of description, fig. 5 is taken as an example to illustrate that the second inner tube K3 and the second outer tube K4 are diodes, and the implementation processes and principles of fig. 3, 4, 6-13, and the second inner tube K3 and the second outer tube K4 are the same as those of reverse conducting transistors, which are not repeated herein, and the working principle of the floating capacitor type three-level Buck circuit is as follows:
s401, controlling an outer tube connected with the charging unit to be conducted and an inner tube connected with the charging unit to be cut off, and charging the floating capacitor of the floating capacitor type three-level Buck circuit.
The outer tube connected to the charging unit 311 is a first outer tube K1, and the inner tube connected to the charging unit 311 is a first inner tube K2, i.e. the first outer tube K1 is controlled to be turned on and the first inner tube K2 is controlled to be turned off; the loop current trend at this time is: the input capacitor Cin → the first outer tube K1 → the floating capacitor Cf → the second inner tube K3 → the inductor L → the output capacitor Co → the input capacitor Cin, i.e., the floating capacitor Cf charges;
s402, controlling the inner pipe and the outer pipe which are connected with the charging unit to be turned off, and charging the suspension capacitor and the charging unit.
Specifically, the first outer tube K1 and the first inner tube K2 are both controlled to be turned off, and the loop current trend at this time is as follows: the input capacitor Cin → the charging diode D1 of the charging unit 311 → the balance capacitor C1 of the charging unit 311 → the floating capacitor Cf → the second outer tube K4 → the input capacitor Cin, that is, the balance capacitor C1 and the floating capacitor Cf of the charging unit 311 are charged simultaneously; meanwhile, the inductor L → the output capacitor Co → the second outer tube K4 → the second inner tube K3 → the inductor L, i.e. the inductor L is in current freewheeling.
And S403, controlling the outer pipe connected with the charging unit to be turned off and the inner pipe connected with the charging unit to be turned on to charge the charging unit.
Specifically, the first outer tube K1 is controlled to be turned off, and the first inner tube K2 is controlled to be turned on; the loop current trend at this time is: the input capacitor Cin → the charging diode D1 of the charging unit 311 → the balance capacitor C1 of the charging unit 311 → the first inner tube K2 → the inductor L → the output capacitor Co → the input capacitor Cin, i.e., the balance capacitor C1 of the charging unit 311.
After step S403 is completed, the process returns to step S401, i.e., steps S401 to S403 are executed in a loop until the voltage of the floating capacitor Cf rises to be equal to half of the input voltage. Since the conduction time of the first outer tube K1 and the first inner tube K2 in one switching period T is equal to D × T, and D is a conduction duty ratio, the voltage division of the balance capacitor C1 of the charging unit 311 and the voltage division of the floating capacitor Cf are equal, and increase with the accumulation of the working time until the voltage is half of the input voltage.
Therefore, when the voltages of the floating capacitor Cf and the balance capacitor C1 are half lower than the input voltage, in the working process of the floating capacitor type three-level Buck circuit, only the floating capacitor Cf charging circuit is used, but the floating capacitor Cf discharging circuit is not used, and the speed of charging the floating capacitor Cf to a stable state in the dynamic adjustment of the floating capacitor type three-level Buck circuit is accelerated through the charging unit 311.
After the voltage of the floating capacitor Cf rises to be equal to half of the input voltage, step S302 may further include steps S404 to S406 that are cyclically performed.
It should be noted that, after the voltage of the balance capacitor C1 of the charging unit 311 and the voltage of the floating capacitor Cf rise to half of the input voltage, the first inner tube K2 is turned on, so that the voltage of the balance capacitor C1 is greater than Vin/2, at this time, Vc1+ Vf > Vin, Vc1 is the voltage of the balance capacitor C1, Vf is the voltage of the floating capacitor Cf, and Vin is the input voltage, therefore, the charging diode D1 is turned off in the reverse direction, for convenience of description, in the following description, Vc1 is the voltage of the balance capacitor C1, Vf is the voltage of the floating capacitor Cf, Vin is the input voltage, and Vout is the output voltage.
And S404, controlling the outer pipe connected with the charging unit to be conducted and the inner pipe connected with the charging unit to be disconnected so as to charge the floating capacitor.
Specifically, the first outer tube K1 is controlled to be on, and the first inner tube K2 is controlled to be off, at this time, the loop current trend is as follows: the input capacitor Cin → the first outer tube K1 → the floating capacitor Cf → the second inner tube K3 → the inductor L → the output capacitor Co → the input capacitor Cin, i.e. the floating capacitor Cf, is charged, and the voltage of the inductor L is Vin-Vf-Vout.
S405, controlling the inner pipe and the outer pipe which are connected with the charging unit to be turned off, and enabling the suspension capacitor and the charging unit not to be charged and discharged.
Specifically, the first outer tube K1 and the first inner tube K2 are both controlled to be turned off, and the loop current trend at this time is as follows: the inductor L → the output capacitor Co → the second outer tube K4 → the second inner tube K3 → the inductor L, i.e. the inductor L has current flowing, the balance capacitor C1 and the floating capacitor Cf have no charge or discharge, the voltage thereof remains unchanged, and the voltage of the inductor L is-Vout.
And S406, controlling the outer pipe connected with the charging unit to be turned off and the inner pipe connected with the charging unit to be turned on, and discharging the floating capacitor.
Specifically, the first outer tube K1 is controlled to be turned off, the first inner tube K2 is controlled to be turned on, and the loop current trend at this time is as follows: the floating capacitor Cf → the first inner tube K2 → the inductor L → the output capacitor Co → the second outer tube K4 → the floating capacitor Cf, i.e. the floating capacitor Cf discharges, and the voltage of the inductor L is Vf-Vout.
It should be noted that the output voltage can be obtained according to the inductive volt-second balance principle; the formula adopted is as follows: the expression can be derived in the same way when the value is 0.5< D <1, and is not repeated herein, and is within the protection scope of the present application.
Therefore, if the parameters of the floating capacitive three-level Buck circuit are ideal, the balance capacitor C1 of the charging unit 311 does not participate in the work of the floating capacitive three-level Buck circuit during normal work, that is, there is no charging and discharging process, and the voltage remains unchanged; the floating capacitor Cf is charged and discharged equally during the period of the first outer tube K1 and the first inner tube K2 being alternately conducted, and the average voltage of the floating capacitor Cf is kept at half the input bus voltage.
In practical application, due to parameter difference, the voltage Vf of the floating capacitor Cf slightly deviates from the half-input bus voltage Vin/2; as can be seen from the above analysis, the floating capacitor Cf is charged when only the first outer tube K1 is turned on, the floating capacitor Cf is discharged when only the first inner tube K2 is turned on, and if the on duty ratios of the first outer tube K1 and the first inner tube K2 are the same as D, the gain of the output voltage and the input voltage is fixed, and at this time, the duty ratio fine adjustment amount Δ D with opposite signs is superimposed on the on duty ratios D of the first outer tube K1 and the first inner tube K2, so that the charge and discharge control of the floating capacitor Cf can be realized, and the voltage control of the floating capacitor Cf can be further realized.
During normal operation, if the floating capacitor Cf is not in a steady state when the input voltage suddenly changes, the floating capacitor Cf only has a charging loop, and the floating capacitor Cf quickly enters the steady state, which is described in steps S401 to S403 for details, and is not described here again.
In the embodiment, the circuit still rapidly enters a steady state even when the voltage of the input voltage source suddenly changes, the normal working complexity of the circuit is not increased, and the performance of the floating capacitance type three-level Buck circuit is improved.
In addition, in this embodiment, if the inner tube and the outer tube that are not connected to the charging unit 311 are MOS (Metal Oxide Semiconductor) tubes, the two inner tubes and the two outer tubes in the floating capacitor type three-level Buck circuit are controlled to be complementarily turned on, or the inner tube and the outer tube that are not connected to the charging unit are controlled to be kept in an off state.
Specifically, the outer tube connected to the charging unit 311 and the inner tube not connected to the charging unit 311 are both controlled to be turned on, and the inner tube connected to the charging unit 311 and the outer tube not connected to the charging unit 311 are both controlled to be turned off. Namely, the first outer tube K1 and the second inner tube K3 are both turned on, and the first inner tube K2 and the second outer tube K4 are both turned off. Then controlling the two inner pipes and the two outer pipes to be closed; namely, the first outer tube K1, the first inner tube K2, the second inner tube K3 and the second outer tube K4 are all closed. Then, the outer tube connected with the charging unit 311 and the inner tube not connected with the charging unit 311 are controlled to be turned off, and the inner tube connected with the charging unit 311 and the outer tube not connected with the charging unit 311 are controlled to be turned on; namely, the first outer tube K1 and the second inner tube K3 are both off, and the first inner tube K2 and the second outer tube K4 are both on.
Or the outer tube which is connected with the charging unit is firstly controlled to be switched on, and the two inner tubes and the outer tube which is not connected with the charging unit are both controlled to be switched off; namely, the first outer tube K1 is turned on, and the first inner tube K2, the second inner tube K3 and the second outer tube K4 are all turned off. And controlling the two inner pipes and the two outer pipes to be closed, namely the first outer pipe K1, the first inner pipe K2, the second inner pipe K3 and the second outer pipe K4 to be closed. And then controlling the inner tube connected with the charging unit to be switched on, switching off the two outer tubes and the inner tube not connected with the charging unit, namely switching on the first inner tube K2, and switching off the first outer tube K1, the second inner tube K3 and the second outer tube K4.
The structure and principle of the floating capacitive three-level Buck circuit can be obtained by referring to the above embodiments, and are not described in detail here.
Referring to fig. 16, a schematic diagram of a conventional floating capacitor type n +1 level bridge circuit is shown, where n is a positive integer greater than 1. When the circuit normally works, the voltage of the floating capacitor Cfa is controlled to be (n-a) Vin/n, the withstand voltage of each power tube is Vin/n, wherein a is more than or equal to 1 and less than or equal to n-1, and Vin is input voltage. At the moment of powering on the circuit, the voltage stress of the power tube K1 at the head position is caused to be too high; moreover, when the first power tube is turned on to charge the floating capacitor, the voltage stress of the last power tube K2n is too high, so that both the power tube K1 and the power tube K2n are at risk of overvoltage damage.
Based on the above, the invention provides a suspension capacitance type multi-level bridge circuit, which aims to solve the problem that in the prior art, the voltage stress of a power tube at the head position is too high at the moment of electrifying the circuit; moreover, when the first power tube is conducted to charge the floating capacitor, the voltage stress of the last power tube is too high, so that the first power tube and the last power tube are both in overvoltage damage risk.
The floating capacitive multilevel bridge circuit, see fig. 17, includes: an input capacitor Cin, an output circuit 20, and at least one bridge arm (here, the number of bridge arms is 1 as an example); the bridge arm includes: the capacitive type voltage-reducing circuit comprises a suspension capacitive type n +1 level voltage-reducing conversion unit and n-1 charging units; n is a positive integer greater than 1; wherein:
and the positive and negative electrodes of the input end of the suspension capacitance type n +1 level step-down conversion unit are used as the positive and negative electrodes of the input end of the bridge arm and are respectively connected with the two ends of the input capacitor Cin. The input capacitor Cin may include one capacitor or may include a plurality of capacitors, which are not specifically limited herein and are within the scope of the present application.
The floating capacitance type n +1 level buck conversion unit comprises: the inductor L, the upper bridge arm branch, the lower bridge arm branch and n-1 floating capacitors (Cf 1-Cfn-1 shown in figure 17).
Specifically, the upper arm branch includes n power transistors (e.g., K1 to Kn shown in fig. 17) connected in series in sequence, the lower arm branch includes n power transistors (e.g., Kn +1 to K2n shown in fig. 17) connected in series in sequence, and a connection point between each two power transistors serves as a node (e.g., 2 to n shown in fig. 17, each node of the lower arm branch is not shown). One end of the upper bridge arm branch is used as the positive electrode of the input end of the suspension capacitance type n +1 level buck conversion unit, that is, the positive electrode of the input end of the bridge arm is connected with the positive electrode of the input capacitor Cin, and the connection point is also used as a node (1 shown in fig. 17); the other end of the upper bridge arm branch is connected with one end of the lower bridge arm branch, the connection point is used as the midpoint of the suspension capacitance type n +1 level step-down conversion unit, and the connection point is also used as a node (n +1 shown in fig. 17); the other end of the lower bridge arm branch is used as the negative electrode of the input end of the suspension capacitance type n +1 level step-down conversion unit, namely the negative electrode of the input end of the bridge arm, and is connected with the negative electrode of the input capacitor Cin, and the connection point is also used as a node.
Furthermore, power tubes K1 to K2n are connected in series in sequence, one end of the power tube K1 is used as the positive electrode of the input end of the floating capacitive type n +1 level step-down converting unit and is connected with the positive electrode of the input capacitor Cin, and one end of the power tube K2n is used as the positive electrode of the input end of the floating capacitive type n +1 level step-down converting unit and is connected with the negative electrode of the input capacitor Cin.
When each charging unit is connected to the positive electrode of the corresponding floating capacitor, each power tube in the upper bridge arm branch is a main power control switching tube and can be a reverse conducting transistor, and each power tube in the lower bridge arm branch is a follow current tube of an inductor L and can be a diode or a reverse conducting transistor; when each charging unit is respectively connected with the negative electrode of the corresponding suspension capacitor, each power tube in the lower bridge arm branch is a main power control switch tube and can be a reverse conducting transistor, and each power tube in the upper bridge arm branch is a follow current tube of an inductor L and can be a diode or a reverse conducting transistor. The reverse conducting transistor can be a MOSFET or an IGBT integrated with a reverse parallel diode.
It should be noted that, when n is 2, the floating capacitance type multilevel bridge circuit is the three-level circuit described in the above embodiment, and at this time, the upper arm branch and the lower arm branch both include two power transistors. In the upper bridge arm branch, a power tube which is connected with the midpoint is an inner tube, and a power tube which is not connected with the midpoint is an outer tube; in the lower bridge arm branch, the power tube which is connected with the midpoint is an inner tube, and the power tube which is not connected with the midpoint is an outer tube. That is, the power tube not connected to the midpoint is equivalent to the outer tube of the above-described embodiment, and the power tube connected to the midpoint is equivalent to the inner tube of the above-described embodiment.
One end of the inductor L is connected to the midpoint, i.e., the node n +1, and the other end is used as an output end of the floating capacitive type n +1 level step-down conversion unit, i.e., an output end of the bridge arm, and is connected to the first end of the output circuit 20.
When the floating capacitance type multilevel bridge circuit is applied to a multilevel Buck circuit, the second end N of the output circuit 20 is connected to another output end of the bridge arm, specifically, if each charging unit is connected to the positive electrode of the corresponding floating capacitance, the second end N of the output circuit 20 is connected to the negative electrode of the input end of the floating capacitance type N +1 level Buck conversion unit, specifically, referring to fig. 22, the positive electrode of the output capacitance Co in the output circuit 20 is connected to one end of the inductance L, and the negative electrode of the output capacitance Co in the output circuit 20 is connected to the negative electrode of the input capacitance Cin; if each charging unit is connected to the negative electrode of the corresponding floating capacitor, the input terminal of the N-floating capacitor type N +1 level buck conversion unit at the second end of the output circuit 20 is connected to the positive electrode. At this time, the floating capacitance type multilevel bridge circuit is a floating capacitance type multilevel Buck circuit.
When the floating capacitive multilevel bridge circuit is applied to a multilevel bridge inverter circuit, the second terminal N of the output circuit 20 is connected to other circuits or to the midpoint of the input capacitor Cin, that is, the floating capacitive multilevel bridge circuit is a floating capacitive multilevel bridge inverter circuit.
In addition, the second end N of the output circuit 20 may also be connected to other potential points of the floating capacitive type N +1 level buck conversion unit, which is not specifically limited herein and is determined according to the specific application environment, and is within the protection scope of the present application.
One end of each suspension capacitor is connected with each node in the upper bridge arm branch in a one-to-one correspondence mode, and the other end of each suspension capacitor is connected with the symmetrical nodes in the lower bridge arm branch in a one-to-one correspondence mode. Specifically, one end of the floating capacitor Cf1 is connected with a connection point between the power tubes K1 and K2 in the upper bridge arm branch, namely a node 2, and the other end of the floating capacitor Cf1 is connected with a connection point between the power tubes K2n and K2n-1 in the lower bridge arm branch; one end of the suspension capacitor Cf2 is connected with a connection point between the power tubes K2 and K3 in the upper bridge arm branch, namely a node 3, and the other end of the suspension capacitor Cf2 is connected with a connection point between the power tubes K2n-1 and K2n-2 in the lower bridge arm branch; by analogy, one end of the floating capacitor Cfn-2 is connected with a connection point between the power tubes Kn-1 and Kn-2 in the upper bridge arm branch, namely a node n-1, and the other end of the floating capacitor Cfn-2 is connected with a connection point between the power tubes Kn +2 and Kn +3 in the lower bridge arm branch; one end of the suspension capacitor Cfn-1 is connected with a connection point between the power tubes Kn and Kn-1 in the upper bridge arm branch, namely a node n, and the other end of the suspension capacitor Cfn-1 is connected with a connection point between the power tubes Kn +1 and Kn +2 in the lower bridge arm branch.
It should be noted that each charging unit has two connection relationships, and the two connection relationships are described here as follows:
(1) the output end of each charging unit is connected to the positive electrode of the corresponding floating capacitor in the floating capacitor type n +1 level step-down converting unit, the input end of each charging unit (as shown in a1 to an-1 in fig. 17) is connected to any node of the upper bridge arm branch of the floating capacitor type n +1 level step-down converting unit, where the voltage of the node is higher than the voltage of the first preset connection point, and the voltage of the first preset connection point is the voltage of the positive electrode of the corresponding floating capacitor and the connection point of the corresponding power tube.
According to the connection relationship of the suspension capacitors, one end of the suspension capacitor connected with the corresponding node in the upper bridge arm branch is used as the positive electrode of the suspension capacitor, and one end of the suspension capacitor connected with the corresponding node in the lower bridge arm branch is used as the negative electrode of the suspension capacitor. Furthermore, the output end of each charging unit is respectively connected with one end of the corresponding floating capacitor and the corresponding node in the upper bridge arm branch.
It should be noted that, the voltage of the node close to the positive electrode of the input terminal in the floating capacitor type n +1 level buck conversion unit is higher than the voltage of the node far from the positive electrode of the input terminal. Specifically, the voltage of the node 1 is higher than the voltage of the node 2, and the voltage of the node n-1 is higher than the voltage of the node n, so on, which is not described in detail herein.
That is, in this case, as long as the voltage of the node connected to the input terminal of each charging unit is higher than the voltage of the node connected to the respective output terminal, that is, the output terminal of the charging unit a is connected to the node a +1, the input terminal aa is connected to the node i, where a is greater than or equal to 1 and less than or equal to n-1, and i is greater than or equal to 1 and less than or equal to a. For example, if a is 2, the output of charging unit 2 is connected to node 3, and its input, i.e., terminal a2, is connected to node 2 or 1.
Specifically, one end of the charging unit 1 and one end of the floating capacitor Cf1 are both connected to the node 2, and the other end a1 of the charging unit 1 is connected to the node 1; one end of the charging unit 2 and one end of the floating capacitor Cf2 are both connected with the node 3, and the other end a2 of the charging unit 2 is connected with the node 1 or 2; by analogy, one end of the charging unit n-2 and one end of the floating capacitor Cfn-2 are both connected with the node n-1, and the other end an-2 of the charging unit n-2 is connected with any one of the nodes 1 to n-2; one end of the charging unit n-1 and one end of the floating capacitor Cfn-1 are both connected with the node n, and the other end an-1 of the charging unit n-1 is connected with any one of the nodes 1 to n-1.
For convenience of explanation, the floating capacitor type n +1 level buck conversion unit is exemplified as a floating capacitor type 4 level buck conversion unit, and refer to fig. 18.
The power tubes K1-K6 are sequentially connected in series, one end of the power tube K1, namely the node 1, is respectively connected with one end of the charging unit 1 and the anode of the input capacitor Cin, a connection point between the power tubes K3 and K4, namely the node 4, is connected with the first end of the output circuit 20 through the inductor L, and one end of the power tube K6 is connected with the cathode of the input capacitor Cin; the second terminal N of the output circuit 20 is connected to the negative electrode of the input capacitor Cin, or connected to the midpoint of the input capacitor Cin, or connected to another potential point of the floating capacitor type N +1 level buck conversion unit, or connected to another circuit.
The other end of the charging unit 1 and one end of the floating capacitor Cf1 are both connected with a node 2 which is a connection point between the power tubes K1 and K2, and the other end of the floating capacitor Cf1 is connected with a connection point between the power tubes K5 and K6.
One end of the charging unit 2 is connected with a connection point between the power tubes K1 and K2, namely, a node 2, or is connected with one end of the power tube K1, namely, a node 1; the other end of the charging unit 2 and one end of the floating capacitor Cf2 are both connected to a node 3 which is a connection point between the power tubes K2 and K3, and the other end of the floating capacitor Cf2 is connected to a connection point between the power tubes K4 and K5.
(2) The input end of each charging unit is respectively connected with the negative electrode of the corresponding suspension capacitor in the suspension capacitor type n +1 level step-down conversion unit; the output end of each charging unit is respectively connected with any node, of which the voltage in the lower bridge arm branch of the suspension capacitance type n +1 level buck conversion unit is lower than the voltage of a second preset connection point; the voltage of the second preset connection point is the voltage of the connection point of the negative electrode of the corresponding suspension capacitor and the corresponding power tube.
In this case, it is also ensured that the voltage of the node to which the input terminals of the respective charging units are connected is lower than the voltage of the node to which the respective output terminals are connected. It should be noted that the nodes 1-n of the upper bridge arm branch are respectively symmetrical to the corresponding nodes of the lower bridge arm branch. Specifically, one end of the charging unit 1 and one end of the floating capacitor Cf1 are both connected to the symmetric node of the node 2, and the other end a1 of the charging unit 1 is connected to the symmetric node of the node 1; one end of the charging unit 2 and one end of the floating capacitor Cf2 are both connected with the symmetrical node of the node 3, and the other end a2 of the charging unit 2 is connected with the symmetrical node of the node 1 or 2; by analogy, one end of the charging unit n-2 and one end of the floating capacitor Cfn-2 are both connected with the symmetrical node of the node n-1, and the other end an-2 of the charging unit n-2 is connected with the symmetrical node of any node from the nodes 1 to n-2; one end of the charging unit n-1 and one end of the floating capacitor Cfn-1 are both connected with the symmetrical node of the node n, and the other end an-1 of the charging unit n-1 is connected with the symmetrical node of any one of the nodes 1 to n-1.
It should be noted that (2) the more detailed connection relationship is similar to the structure in (1), and is not described herein again, which is within the scope of the present application.
In practical application, before the floating capacitance type multi-level bridge circuit enters a normal working state after being powered on, each charging unit is in a conducting state, so that the voltage on the corresponding floating capacitance is charged to a preset range of the steady-state voltage on the floating capacitance after the floating capacitance type multi-level bridge circuit enters the normal working state through the voltage division of each charging unit and each floating capacitance. Specifically, the steady-state voltage may be set as an upper limit value within a preset range of the steady-state voltage, and a value obtained by subtracting a preset value from the steady-state voltage may be set as a lower limit value, where the preset value may be set to a smaller value, so that the voltage across the corresponding floating capacitor is charged as close as possible to the steady-state voltage of the floating capacitor type multi-level bridge circuit after the floating capacitor type multi-level bridge circuit enters a normal operating state.
In this embodiment, when the floating capacitor type multilevel bridge circuit is powered on, most of the input voltages originally applied to the two ends of the power tube which is at the first/last position and serves as the main power control switch tube are greatly reduced by dividing the voltages through the corresponding charging units and the corresponding floating capacitors, so that the power tube is prevented from being damaged by overvoltage; meanwhile, the corresponding floating capacitor is pre-charged through the corresponding charging unit, and the problem that the power tube which is at the first position/the last position and is used as a follow current switch tube is damaged by overvoltage due to the fact that the power tube is conducted to charge the floating capacitor can be avoided, so that the safety of the floating capacitor type multi-level bridge circuit is improved.
In addition, referring also to fig. 17, the floating capacitance type multilevel bridge circuit further includes: a clamping circuit 10.
The input end of the clamping circuit 10 is connected with the midpoint of the floating capacitive type n +1 level step-down conversion unit, i.e. the node n +1, and the output end of the clamping circuit 10 is connected with the negative electrode of the input end of the floating capacitive type n +1 level step-down conversion unit, i.e. the output end of the clamping circuit 10 is respectively connected with one end of the power tube K2n and the negative electrode of the input capacitor Cin.
Specifically, referring to fig. 18, the input terminal of the clamp circuit 10 is connected to the connection point between the power transistors K3 and K4, i.e., the node 4, and one end of the inductor L, respectively; the output end of the clamping circuit 10 is respectively connected with one end of the power tube K6 and the negative electrode of the input capacitor Cin.
When the floating capacitive multilevel bridge circuit is applied to a multilevel Buck circuit, referring to fig. 21, one end of the clamp circuit 10 is connected to the midpoint and one end of the inductor L, respectively, and the other end of the clamp circuit 10 is connected to the negative electrode of the input capacitor Cin. The connection relationship of the output capacitor Co can be referred to the above embodiments, and is not described in detail here. Of course, as shown in fig. 21, the clamp circuit 10 may be omitted.
When the floating capacitive multilevel bridge circuit is powered on, each charging unit and the clamping circuit 10 are in a conducting state, and each charging unit charges a corresponding floating capacitor; meanwhile, the clamp circuit 10 clamps the potential of the midpoint (node n +1 shown in fig. 17, node 4 shown in fig. 8) of the floating capacitive type n +1 level step-down conversion unit to a lower voltage, so as to ensure that each floating capacitor is charged to a higher voltage; the problem that the corresponding power tube is damaged due to overvoltage caused by too low voltage of the suspension capacitor in the subsequent starting process is solved; until the voltage on the corresponding suspension capacitor is charged to be within the preset range of the corresponding steady-state voltage, each charging unit is in a cut-off state, so that each charging unit stops charging the corresponding suspension capacitor; meanwhile, the clamp circuit 10 is in a cut-off state, that is, the clamp circuit 10 stops clamping, and the subsequent circuit is switched into a normal working state.
Specifically, as shown in fig. 17, the charging unit 1 charges the floating capacitor Cf1, the charging unit 2 charges the floating capacitor Cf2, and so on, the charging unit n-2 charges the floating capacitor Cfn-2, and the charging unit n-1 charges the floating capacitor Cfn-1.
The steady state voltages of different floating capacitors are different, and the steady state voltages are respectively as follows: (n-a) × Vin/n, therefore, the steady-state voltage of the floating capacitor is related to the position of the floating capacitor in the circuit, as shown in fig. 17, the steady-state voltage of the floating capacitor Cf1 is (n-1) × Vin/n, which is the highest voltage in each floating capacitor, and the steady-state voltage of the floating capacitor Cfn-1 is Vin/n, which is the lowest voltage in each floating capacitor.
Optionally, each of the charging units includes: a balancing capacitor and a charging diode connected in series.
If the charging units are respectively connected with the anodes of the corresponding floating capacitors, two connection relations exist between the balance capacitor and the charging diode in one charging unit, as follows:
(1) the negative electrode of the balance capacitor is connected with the anode of the charging diode; the cathode of the charging diode is used as the output end of the charging unit and is respectively connected with the anode of the corresponding suspension capacitor and the corresponding node in the suspension capacitor type 4-level step-down conversion unit; and the anode of the balance capacitor is used as the input end of the charging unit and is connected with any node of the suspension capacitance type 4-level step-down conversion unit, the voltage of which is higher than the voltage of a preset connection point.
Specifically, in the charging unit a, the negative electrode of the balance capacitor is connected with the anode of the charging diode; the cathode of the charging diode is respectively connected with the anode of the floating capacitor Cfa and the node a +1 in the floating capacitor type n +1 level buck conversion unit, and the anode of the balance capacitor is connected with any one point from the node 1 to the node a in the floating capacitor type n +1 level buck conversion unit.
Referring to fig. 19 (which illustrates a floating capacitive 4-level buck converter unit as an example), the cathode of the balancing capacitor C1 is connected to the anode of the charging diode D1; the cathode of the charging diode D1 is respectively connected with the anode of the suspension capacitor Cf1 and the connection point between the power tubes K1 and K2; the anode of the balancing capacitor C1 is connected to the junction between the power transistor K1 and the input capacitor Cin. The cathode of the balance capacitor C2 is connected with the anode of the charging diode D2; the cathode of the charging diode D1 is respectively connected with the anode of the suspension capacitor Cf2 and the connection point between the power tubes K2 and K3; the anode of the balancing capacitor C2 is connected to the junction between the power transistor K1 and the input capacitor Cin, or to the junction between the power transistors K1 and K2.
(2) The positions of the balance capacitor and the charging diode are exchanged. Namely, the anode of the balance capacitor is connected with the cathode of the charging diode, the anode of the charging diode is used as the input end of the charging unit, and the cathode of the balance capacitor is used as the output end of the charging unit. Specifically, in the charging unit a, the anode of the balance capacitor is connected with the cathode of the charging diode; the negative pole of the balance capacitor is respectively connected with the positive pole of the floating capacitor Cfa and the node a +1 in the floating capacitor type n +1 level buck conversion unit, and the anode of the charging diode is connected with any one point from the node 1 to the node a in the floating capacitor type n +1 level buck conversion unit.
When the floating capacitive type n +1 level buck conversion unit is the floating capacitive type 4 level buck conversion unit, the specific connection relationship between the balance capacitor and the charging diode is similar to that shown in fig. 19, which is not described herein again one by one, and is all within the protection scope of the present application.
It should be noted that each charging unit may adopt any one of the two structures; part of the charging units can adopt the structure of (1), and the other part of the charging units can adopt the structure of (2); it is not specifically limited herein but is within the scope of the present application.
When the anode voltage of the charging diode is higher than the cathode voltage of the charging diode, the charging diode is conducted to charge the corresponding suspension capacitor; when the anode voltage of the charging diode is lower than the cathode voltage of the charging diode, the charging diode is cut off, and the charging of the corresponding floating capacitor is stopped.
It is worth to be noted that, in the prior art, it is also proposed to provide a switch at the input side of the circuit and to provide an additional charging source for each floating capacitor; after the extra charging power supply charges the floating capacitor to the preset voltage, the switch on the input side is closed and the extra charging power supply is disconnected, however, the scheme is complex to implement, and if misoperation occurs, fault damage is easy to occur, and the cost is high.
In the embodiment, compared with the scheme of charging by adopting an additional charging power supply in the prior art, the use of the additional charging power supply is avoided; in addition, the on-off state of a charging diode in the charging unit does not need to be additionally controlled, the complexity of realization is reduced, further, the fault damage is avoided, the cost is reduced, and the safety of the suspension capacitance type multi-level bridge circuit is improved.
Optionally, referring to fig. 17, each charging unit is connected in parallel to each corresponding power tube (e.g., K1 to Kn-1 shown in fig. 17) in the upper arm branch that is not connected to the midpoint in a one-to-one correspondence manner, that is, a series branch of the balancing capacitor and the charging diode is connected in parallel to one power tube. Specifically, taking the floating capacitor type 4-level buck converter as an example for description, referring to fig. 19, a series branch of a balance capacitor C1 and a charging diode D1 is connected in parallel with a power tube K1; the series branch of the balance capacitor C2 and the charging diode D2 is connected with the power tube K2 in parallel.
Each charging unit and the corresponding power tube are in parallel connection, so that the corresponding power tube can be prevented from overvoltage damage by reasonably selecting the capacitance value of each charging unit. Specifically, the steady-state voltage of each charging unit after normal operation is adjusted by configuring the capacitance value of the balance capacitor in each charging unit, so as to adjust the voltage at two ends of the corresponding power tube. The capacitance values of the balancing capacitors are configured in relation to the preset voltage values required to be stabilized after the circuit is powered on, so that overvoltage damage of the corresponding power tube is avoided by configuring the capacitance values of the balancing capacitors, and the capacitance value configuration process of the balancing capacitors is described in the following.
In this embodiment, at the moment of power-on of the circuit, each charging unit charges a corresponding floating capacitor, and meanwhile, the charging unit is connected in parallel with a corresponding power tube, and the capacitance value of each charging unit is configured, so as to ensure that the corresponding power tube is not damaged by overvoltage, and improve the safety of the floating capacitor type multilevel bridge circuit.
In practical application, each suspension capacitor is provided with a parallel sampling resistor to stabilize the voltage of each suspension capacitor at a corresponding preset voltage value, and therefore, a voltage dividing resistor with a corresponding resistance value is also provided for each balance capacitor according to a resistor voltage dividing relationship, that is, the resistance value of each voltage dividing resistor is related to the corresponding steady-state voltage of the balance capacitor connected in parallel, that is, related to the capacitance value of the corresponding balance capacitor, so as to ensure that the voltage of each charging unit can be stabilized at the corresponding preset voltage value after the circuit is powered on, such as the steady-state voltage in a normal working state.
Alternatively, referring to fig. 19 (which illustrates a floating capacitive 4-level bridge circuit as an example), the clamp circuit 10 includes: a clamping capacitor C3 and a third switch T7 connected in series.
The negative electrode of the clamping capacitor C3 is connected with one end of a third switch T7; the positive electrode of the clamping capacitor C3 is used as the input end of the clamping circuit 10 and is respectively connected with the connection point between the inductor L and the power tubes K3 and K4; the other end of the third switch T7 is used as the output end of the clamp circuit 10, and is connected to one end of the power transistor K6 and the negative electrode of the input capacitor Cin, respectively.
Alternatively, the positions of the clamp capacitor C3 and the third switch T7 are reversed. Specifically, the anode of the clamping capacitor C3 is connected to one end of the third switch T7; the other end of the third switch T7 is used as the input end of the clamp circuit 10 and is connected to the connection point between the inductor L and the power transistors K3 and K4, respectively, and the negative electrode of the clamp capacitor C3 is used as the output end of the clamp circuit 10 and is connected to one end of the power transistor K6 and the negative electrode of the input capacitor Cin, respectively.
The third switch T7 may be a mechanical third switch or a power third switch, and specifically may be any one of a relay, an IGBT, and a MOSFET, and is preferably a normally closed relay.
Before each power tube (such as K1 to K6 shown in fig. 19) performs an operation in a normal operating state, the third switch T7 is kept in a normally-closed state, so that the clamp capacitor C3 clamps the voltage of the node 4 to a lower voltage, the floating capacitors Cf1 and Cf2 are ensured to be charged to a higher voltage, and overvoltage damage to the power tubes K2 and K3 due to too low voltages of the floating capacitors Cf1 and Cf2 in subsequent starting is avoided; after the respective power transistors (K1 to K6 shown in fig. 19) start to be ready to perform actions in the normal operation state, the above-described third switch T7 is in the off state.
Specifically, the third switch T7 is held in a normally closed state until the circuit is powered on. After the circuit is powered on, whether each suspension capacitor voltage is charged to the corresponding threshold voltage is detected, when each suspension capacitor voltage is charged to the corresponding threshold voltage and the circuit is ready to operate, the third switch T7 is controlled to be in a turn-off state, and then the circuit enters a normal working state by controlling the on-off state of each power tube. In addition, the corresponding devices capable of determining the starting preparation of each power tube to execute actions in the prior art are all within the protection scope of the present application.
Optionally, in any of the above embodiments, the bridge arm further includes: n-1 discharge cells. The discharge unit is used for discharging corresponding balance capacitors after the suspension capacitance type multi-level bridge circuit is powered down.
In practical applications, each discharge cell includes a discharge diode; if at least one charging unit is connected with the anode of the input capacitor, the anode of the discharging diode is connected with the cathode of the input capacitor and the cathode of the input end of the bridge arm, and the cathode of the discharging diode is connected with the cathode of the corresponding balance capacitor; if at least one charging unit is connected to the negative electrode of the input capacitor, the cathode of the discharging diode is connected to the positive electrode of the input capacitor and the positive electrode of the input end of the bridge arm, and the anode of the discharging diode is connected to the positive electrode of the corresponding balance capacitor, and the specific connection relationship can be referred to the connection relationship shown in fig. 10 and 9, which is not described herein any more and is within the protection scope of the present application.
After the suspension capacitance type multi-level bridge circuit is electrified, the discharge diode is cut off, and after the suspension capacitance type multi-level bridge circuit is electrified, the discharge diode is conducted, and the discharge diode discharges for the corresponding balance capacitor.
In this embodiment, after the floating capacitive type multi-level bridge circuit, the discharge units quickly discharge for the corresponding balance capacitors, so as to avoid the problem of potential safety hazard during maintenance due to long-time electrification of the balance capacitors in the floating capacitive type multi-level bridge circuit.
Optionally, in any one of the above embodiments, when the input voltage source connected to the floating capacitive type multi-level bridge circuit is a stable input voltage source, the bridge arm further includes: and the current limiting unit is arranged between the stable input voltage source and the input capacitor and is used for limiting the charging current of the parallel parasitic capacitor of the power tube which is not connected with the charging unit and the midpoint when the floating capacitive multilevel bridge circuit is connected into the input voltage source.
The current limiting unit includes: the circuit comprises a first switch, a second switch and a current-limiting resistor; the first switch is connected with the current-limiting resistor in series, and a series branch of the first switch and the current-limiting resistor is connected with the second switch in parallel. For a specific connection relationship, reference may be made to the connection relationship shown in fig. 11, which is not described herein again and is within the protection scope of the present application.
The reason why the current-limiting resistor is connected between the stable input voltage source and the input capacitor Cin is that when the stable input voltage source is a voltage source containing a capacitor, and when the initial voltage of the stable input voltage source is very high, such as 1500V, at the moment that the suspension capacitor type multi-level bridge circuit is connected to the input voltage source, if the current-limiting resistor is not arranged, the capacitor of the stable input voltage source charges the balance capacitor, the suspension capacitor and the parasitic capacitors at the two ends of each power tube which are not connected with the midpoint in the lower bridge arm branch circuit by using a maximum charging current, and as the capacitance values of the balance capacitor and the suspension capacitor are far larger than the parasitic capacitors at the two ends of the power tubes, the voltage division is higher as the capacitance values are smaller according to the capacitance value voltage division principle; therefore, the main voltage of the stable input voltage source is applied to the two ends of the power tube, so that the power tube is damaged due to overvoltage, and the embodiment of the invention is provided with the current-limiting resistor, so that the safety of the circuit is improved.
It should be noted that any one or more of the above circuits may be selected to be used in combination according to the application environment and the user's requirements, and certainly not limited to the above exemplary circuits, other circuits that can pre-charge each floating capacitor to avoid overvoltage damage of the corresponding power transistor are also within the protection scope of the present application.
Here, taking the floating capacitance type 4-level bridge circuit as an example, a specific process of the floating capacitance type 4-level bridge circuit and an arrangement of each device will be described with reference to fig. 19.
After the circuit is powered on, the main charging current of the circuit is converged to the clamping capacitor C3 through the balancing capacitors (such as C1 and C2 shown in fig. 19), the diodes (such as D1 and D2 shown in fig. 19) and the floating capacitors (such as Cf1 and Cf2 shown in fig. 19), and since the parallel capacitors of the power tubes are small and negligible, the circuit at the moment of power-on can be equivalent to a capacitor voltage dividing circuit shown in fig. 20.
In the normal operation process, the voltage of the floating capacitor Cf1 is generally maintained at 2 × Vin/3, and the voltage of the floating capacitor Cf2 is generally maintained at Vin/3, so that the voltages of the floating capacitors are as close as possible to the steady-state voltage in the normal operation at the moment of power-on by configuring the capacitance values of the capacitors C1, C2, C3, Cf1 and Cf2, and the transition time from the startup state to the normal operation state of the circuit is reduced.
Referring to fig. 20, if the voltage of the floating capacitor Cf1 is stabilized to be close to 2 × Vin/3 and the voltage of the floating capacitor Cf2 is stabilized to be close to Vin/3 after the power-on of the circuit is stabilized, the voltage of the clamp capacitor C3 needs to be close to 0, and therefore, the capacitance of the clamp capacitor C3 needs to be much larger than the capacitance of each balance capacitor (e.g., C1 and C2 shown in fig. 20) and each floating capacitor (e.g., Cf1 and Cf2 shown in fig. 20).
Assuming that the capacitance of the clamp capacitor C3 is much larger than the capacitance of each balance capacitor and each floating capacitor, and the voltage of the clamp capacitor C3 is approximately equal to 0 after the circuit is electrically stabilized, the relationship among the voltage Vc1 of the balance capacitor C1, the voltage Vc2 of the balance capacitor C2, and the voltage Vcf2 of the floating capacitor Cf2 is: vc 1-Vc 2-Vcf 2-Vin/3, and the voltage Vcf1 of the floating capacitor Cf1 is 2 Vin/3; it is assumed that the capacitance values of the balance capacitor C2 and the floating capacitor Cf2 are equal, i.e., C2 is equal to Cf2, and the equivalent capacitance value of the parallel branch of the floating capacitor Cf1, the balance capacitor C2 and the floating capacitor Cf2 is 1/2 of the balance capacitor C1, i.e., the equivalent capacitance value of the parallel branch is equal to that of the balance capacitor C1
Figure BDA0002336739540000341
Of course, if the voltage of each floating capacitor needs to be stabilized at other voltage values after the circuit is powered on and stabilized, the selection of the capacitance value of each capacitor (i.e., each floating capacitor and each balance capacitor) can be derived in the same manner, which is not described herein again and is within the protection scope of the present application. When the floating capacitance type multilevel bridge circuit is at other levels, the configuration method is also applicable, and the details are not repeated herein and are within the protection scope of the present application.
Therefore, in order to stabilize the voltage of each floating capacitor at the corresponding operating voltage value, the capacitance value of the clamping capacitor C3 is configured as follows: the capacitance value of the clamping capacitor C3 is greater than the capacitance values of the floating capacitors and the balance capacitors, and the difference between the capacitance value of the clamping capacitor C3 and the capacitance values of the floating capacitors and the balance capacitors is greater than a predetermined capacitance value. In addition, the capacitance value configuration of each floating capacitor and each balance capacitor is referred to the above derivation results.
Meanwhile, when the voltage of each balance capacitor is stabilized to be slightly higher than Vin/3 during normal operation, the diode connected in series with the balance capacitor is in a cut-off state, namely, each balance capacitor does not participate in the current conversion operation, and no large ripple current flows. Therefore, each balance capacitor can be a capacitor with low cost and small ripple current. The capacitance of the clamping capacitor C3 is much larger than that of each floating capacitor and each balance capacitor, and the voltage division is very small, so that a capacitor with low withstand voltage and large capacitance, such as an electrolytic capacitor, can be selected, which is also advantageous in cost and volume.
It should be noted that, in the floating capacitance type multilevel bridge circuit described in the above embodiment, except that before entering the normal operating state, each charging unit is in the on state to automatically charge each floating capacitance to the preset range of the corresponding steady-state voltage, a control method shown in fig. 23 may be used to charge each floating capacitance before entering the normal operating state, where the control method is applied to a controller of the floating capacitance type multilevel bridge circuit, and specifically includes:
and S101, controlling the floating capacitive multi-level bridge circuit to be connected to an input voltage source.
In the initial situation, namely before the input voltage source is connected, the voltage of each device in the floating capacitive multilevel bridge circuit is 0, when the input voltage source is connected into the floating capacitive multilevel bridge circuit, the floating capacitive multilevel bridge circuit is still in a standby state, the voltage of the input capacitor is rapidly charged to the voltage of the input voltage source, and the input voltage source charges the corresponding floating capacitor through each charging unit.
It should be noted that before the floating capacitive multilevel bridge circuit is connected to the input voltage source, each power tube in the floating capacitive multilevel bridge circuit is in an off state, and then before a difference between a voltage of each floating capacitor and a steady-state voltage of the corresponding floating capacitor after the floating capacitive multilevel bridge circuit enters a normal operating state falls below a threshold value, the power tube in the floating capacitive multilevel bridge circuit is kept in the off state, that is, before the difference between the voltage of each floating capacitor and the steady-state voltage corresponding to each floating capacitor falls below the threshold value, each power tube is kept in the off state and whether the difference between the voltage of each floating capacitor and the steady-state voltage corresponding to each floating capacitor falls below the threshold value is continuously determined.
In practical applications, if the floating capacitive multilevel bridge circuit includes a current limiting unit, after step S101, the method may further include:
and controlling the first switch of the current limiting unit to be closed so that the current limiting resistor is connected between the voltage-stabilizing input voltage source and the input capacitor, and further reducing the charging current of the parallel parasitic capacitor of the power tube which is not connected with the charging unit and the midpoint.
When the difference between the voltage of each floating capacitor and the corresponding steady-state voltage is lower than the threshold, the second switch of the current limiting unit is controlled to be closed, so that the current limiting resistor is separated from the voltage-stabilizing input voltage source and the input capacitor, the power loss caused by the current limiting resistor is avoided, and then step S102 is executed.
S102, when the difference value between the voltage of each floating capacitor and the corresponding steady-state voltage of each floating capacitor type multi-level bridge circuit after the floating capacitor type multi-level bridge circuit enters a normal working state is reduced to be smaller than a threshold value, controlling two adjacent power tubes in the floating capacitor type multi-level bridge circuit, which are connected with a charging unit, to be conducted in a staggered mode.
The steady state voltage of each floating capacitor is: (n-a) Vin/n, 1 is more than or equal to a and less than or equal to n-1. That is to say, the steady-state voltages of the different floating capacitors are different, and the steady-state voltages corresponding to the floating capacitors can be referred to the above embodiments, which are not described in detail herein.
In a switching period, among the power tubes connected to the charging unit, the conduction duty ratios of the power tubes at odd number positions and the power tubes at even number positions may be equal or unequal, depending on the specific application environment, and are within the protection scope of the present application. The power tube with the connection relation of the input capacitor is taken as the power tube at the 1 st bit, and the power tube with the connection relation with the middle point is taken as the power tube at the last bit, so that the odd bits comprise the 1 st bit, the 3 rd bit and the like; the even bits include 2 nd bit, 4 th bit, etc.
In practical applications, referring to fig. 24, step S102 may include three steps S201 to S203.
For convenience of description, fig. 17 is taken herein as an example to illustrate that each power transistor not connected to the charging unit is a diode, and the implementation processes and principles of other illustrated structures and each power transistor not connected to the charging unit are the same as those of a reverse conducting transistor, which are not described herein again, and the working principle of the floating capacitive multilevel bridge circuit is as follows:
s201, controlling power tubes which are connected with the charging units and are located at odd-numbered positions to be connected, and controlling power tubes which are connected with the charging units and are located at even-numbered positions to be disconnected, and charging corresponding floating capacitors and corresponding charging units in the floating capacitor type multi-level bridge circuit.
Referring to fig. 17, the power transistors connected to the respective charging units and located at odd-numbered positions include K2i-1 (e.g., K1, K3, etc.), and the power transistors connected to the respective charging units and located at even-numbered positions include K2i (e.g., K2, K4, etc.). i is a positive integer, n is more than or equal to 2i-1, and n is more than or equal to 2 i. Specifically, the power tube K2i-1 (such as K1, K3, and the like) is controlled to be turned on, and the power tube K2i (such as K2, K4, and the like) is controlled to be turned off.
Whether each charging unit and each floating capacitor are charged or not is related to the connection relationship of each charging unit, and is not exemplified here and is within the protection scope of the present application.
And S202, controlling all power tubes connected with the charging units to be turned off, and charging all the floating capacitors and all the charging units.
And S203, controlling the power tubes which are connected with the charging unit and are in odd-numbered positions to be turned off, and controlling the power tubes which are connected with the charging unit and are in even-numbered positions to be turned on, so as to charge the corresponding charging unit and the corresponding floating capacitor.
Referring to fig. 17, the power transistors connected to the respective charging units and located at odd-numbered positions include K2i-1 (e.g., K1, K3, etc.), and the power transistors connected to the respective charging units and located at even-numbered positions include K2i (e.g., K2, K4, etc.). i is a positive integer, n is more than or equal to 2i-1, and n is more than or equal to 2 i. Specifically, the power tube K2i-1 (such as K1, K3, and the like) is controlled to be turned on, and the power tube K2i (such as K2, K4, and the like) is controlled to be turned off.
Whether each charging unit and each floating capacitor are charged or not is related to the connection relationship of each charging unit, and is not exemplified here and is within the protection scope of the present application.
After step S203 is completed, step S201 is executed in a return mode, that is, steps S201 to S203 are executed in a loop until the voltage of each floating capacitor rises to the corresponding steady-state voltage. In one switching period T, the conduction time of two adjacent power tubes which are connected with the charging unit is same as D x T, D is a conduction duty ratio, and the balance capacitor and the suspension capacitor of each charging unit are divided into equal parts and are increased along with the accumulation of working time until corresponding steady-state voltage is obtained.
Therefore, when the voltages of the floating capacitors and the balance capacitors are lower than the respective corresponding steady-state voltages, only the floating capacitor charging circuit is provided but not the floating capacitor discharging circuit in the working process of the floating capacitor type multi-level bridge circuit, and the speed of charging the floating capacitors to the steady state in the dynamic adjustment of the floating capacitor type three-level bridge circuit is accelerated through the charging units.
After the voltage of each floating capacitor rises to be equal to the corresponding steady-state voltage, step S102 may further include steps S204 to S206 that are executed in a loop.
It should be noted that, after the voltage of the balance capacitor of each charging unit and the voltage of each floating capacitor rise to the corresponding steady-state voltage, the corresponding power tube is turned on to make the voltage of the balance capacitor greater than the steady-state voltage thereof, and at this time, the sum of the voltage of the balance capacitor and the voltage of the floating capacitor connected thereto is greater than the voltage of the input power supply, so that the charging diode is turned off in the reverse direction.
And S204, controlling the power tubes which are connected with the charging unit and are positioned at odd numbers to be conducted, and controlling the power tubes which are connected with the charging unit and are positioned at even numbers to be switched off, so as to charge the corresponding floating capacitors.
S205, controlling all power tubes connected with the charging units to be turned off, and enabling all the suspension capacitors and all the charging units not to be charged and discharged.
And S206, controlling the power tubes which are connected with the charging unit and are in odd-numbered positions to be turned off, and controlling the power tubes which are connected with the charging unit and are in even-numbered positions to be turned on, so as to discharge the corresponding floating capacitors.
It should be noted that the output voltage can be obtained according to the inductive volt-second balance principle; the formula adopted is as follows: the expression can be derived in the same way when the value is 0.5< D <1, and is not repeated herein, and is within the protection scope of the present application.
During normal operation, if the input voltage suddenly changes, and each floating capacitor is not in a stable state, the floating capacitor only has a charging loop, and each floating capacitor quickly enters the stable state, for specific description, refer to the above steps S201 to S203, and no further description is given here.
In the embodiment, the circuit still rapidly enters a steady state even when the voltage of the input voltage source suddenly changes, the complexity of normal operation of the circuit is not increased, and the performance of the floating capacitance type multi-level bridge circuit is improved.
In addition, in this embodiment, if each power transistor not connected to the charging unit is a MOS transistor, the method further includes, while executing step S102:
controlling each power tube in the suspension capacitance type multilevel bridge circuit, which is not connected with the charging unit, to be in complementary conduction with the symmetrical power tube connected with the charging unit; or, each power tube which is not connected with the charging unit in the floating capacitance type multi-level bridge circuit is controlled to keep the off state.
The structure and principle of the floating capacitive multilevel bridge circuit can be seen from the above embodiments, and are not described in detail here. The detailed working process and principle of each step in this embodiment can be referred to the working process and principle of the control method of the floating capacitor type three-level Buck circuit described in the above embodiments, which are not described herein again one by one, and are all within the protection scope of this application.
The embodiments in the present specification are described in a progressive manner, and the same and similar parts among the embodiments are referred to each other, and each embodiment focuses on the differences from the other embodiments. In particular, the system or system embodiments are substantially similar to the method embodiments and therefore are described in a relatively simple manner, and reference may be made to some of the descriptions of the method embodiments for related points. The above-described system and system embodiments are only illustrative, wherein the units described as separate parts may or may not be physically separate, and the parts displayed as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the solution of the present embodiment. One of ordinary skill in the art can understand and implement it without inventive effort.
Those of skill would further appreciate that the various illustrative elements and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both, and that the various illustrative components and steps have been described above generally in terms of their functionality in order to clearly illustrate this interchangeability of hardware and software. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the implementation. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (30)

1. A floating capacitor three-level Buck circuit, comprising: an input capacitance, an output capacitance, and at least one leg, the leg comprising: the device comprises a charging unit, a suspension capacitor, two inner pipes, two outer pipes and an inductor; wherein:
two ends of the input capacitor are respectively used as the positive electrode and the negative electrode of the high-voltage side of the suspension capacitor type three-level Buck circuit;
two ends of the output capacitor are respectively used as the positive electrode and the negative electrode of the low-voltage side of the suspension capacitor type three-level Buck circuit;
in the bridge arm, the suspension capacitor is connected in parallel with the series branch of the two inner tubes, a connecting point between the two inner tubes is connected with one end of the inductor, the other end of the inductor is connected with one of the positive and negative electrodes of the low-voltage side, one outer tube is used for respectively connecting the other of the positive and negative electrodes of the low-voltage side and the one of the positive and negative electrodes of the high-voltage side with the same polarity, and the other outer tube is used for connecting the other of the positive and negative electrodes of the high-voltage side and is connected with the charging unit in parallel;
in the bridge arm, an outer pipe and an inner pipe which are connected with the charging unit are conducted in a staggered mode to realize the following steps: charging the floating capacitor, the floating capacitor and the charging unit, and the charging unit; until the voltage of the floating capacitor rises to be equal to half of the input voltage; the input voltage is a voltage across the input capacitor.
2. The suspended capacitive three-level Buck circuit of claim 1, wherein the charging unit comprises: a balancing capacitor and a charging diode connected in series;
if one end of the balance capacitor is connected with the anode of the charging diode, the other end of the balance capacitor is used as the input end of the charging unit, and the cathode of the charging diode is used as the output end of the charging unit;
and if one end of the balance capacitor is connected with the cathode of the charging diode, the other end of the balance capacitor is used as the output end of the charging unit, and the anode of the charging diode is used as the input end of the charging unit.
3. The suspended capacitive three-level Buck circuit of claim 2, further comprising: and the discharging unit is used for discharging the balance capacitor after the suspension capacitance type three-level Buck circuit is powered down.
4. The floating capacitance type three-level Buck circuit according to claim 3, wherein the discharge unit comprises: a discharge diode;
if the low-voltage side negative electrode of the suspension capacitance type three-level Buck circuit is connected with the high-voltage side negative electrode of the suspension capacitance type three-level Buck circuit, the anode of the discharge diode is connected with the low-voltage side negative electrode and the high-voltage side negative electrode, and the cathode of the discharge diode is connected with the charged negative electrode of the balance capacitor;
if the low-voltage-side positive electrode of the suspension capacitance type three-level Buck circuit is connected with the high-voltage-side positive electrode of the suspension capacitance type three-level Buck circuit, the cathode of the discharge diode is connected with the low-voltage-side positive electrode and the high-voltage-side positive electrode, and the anode of the discharge diode is connected with the charged positive electrode of the balance capacitor.
5. The floating capacitance type three-level Buck circuit according to claim 1, further comprising, when an input voltage source connected to the floating capacitance type three-level Buck circuit is a stable input voltage source, between the stable input voltage source and the input capacitor: a current limiting unit;
and the current limiting unit is used for limiting the charging current of the parallel parasitic capacitor of the outer tube which is not connected with the charging unit when the suspension capacitance type three-level Buck circuit is connected to an input voltage source.
6. The suspended capacitive three-level Buck circuit of claim 5, wherein the current limiting unit comprises: the circuit comprises a first switch, a second switch and a current-limiting resistor;
the first switch is connected with the current-limiting resistor in series;
and the series branch of the first switch and the current-limiting resistor is connected with the second switch in parallel.
7. The floating capacitance type three-level Buck circuit according to claim 1, wherein the number of the bridge arms is n, and n is a positive integer greater than or equal to 2.
8. The floating capacitance type three-level Buck circuit according to any one of claims 1 to 7, wherein the inner tube and the outer tube connected to the charging unit are reverse conducting transistors respectively, and are in a staggered conducting state during normal operation;
the inner tube and the outer tube which are not connected with the charging unit are respectively a diode or a reverse conducting transistor.
9. A control method of a floating capacitance type three-level Buck circuit, which is applied to the controller of the floating capacitance type three-level Buck circuit according to any one of claims 1 to 8, the control method comprising:
controlling the suspension capacitance type three-level Buck circuit to be connected to an input voltage source;
and when the difference between the voltage of the floating capacitor and half of the input voltage is reduced to be smaller than a threshold value, controlling the inner tube and the outer tube which are connected with the charging unit in the floating capacitor type three-level Buck circuit to be conducted in a staggered mode.
10. The method for controlling a floating capacitance type three-level Buck circuit according to claim 9, wherein the step of controlling the inner tube and the outer tube of the floating capacitance type three-level Buck circuit, which are connected with a charging unit, to be alternately conducted, comprises:
controlling an outer tube connected with the charging unit to be conducted and an inner tube connected with the charging unit to be switched off so as to charge a floating capacitor of the floating capacitor type three-level Buck circuit;
controlling the inner pipe and the outer pipe which are connected with the charging unit to be turned off, and charging the suspension capacitor and the charging unit;
controlling the outer pipe connected with the charging unit to be switched off and the inner pipe connected with the charging unit to be switched on to charge the charging unit;
and returning to the step of controlling the conduction of the outer pipe connected with the charging unit and the disconnection of the inner pipe connected with the charging unit to charge the floating capacitor of the floating capacitor type three-level Buck circuit until the voltage of the floating capacitor rises to be equal to half of the input voltage.
11. The method of claim 9, wherein said controlling the inner and outer tubes of said floating capacitance type three-level Buck circuit in a connection relationship with a charging unit alternately conducts, further comprising the following three steps performed cyclically after the voltage of said floating capacitance rises to equal to half of said input voltage:
controlling the conduction of an outer pipe connected with the charging unit and the disconnection of an inner pipe connected with the charging unit to charge the floating capacitor;
controlling the inner pipe and the outer pipe which are connected with the charging unit to be turned off, so that the suspension capacitor and the charging unit are not charged and discharged;
and controlling the outer pipe connected with the charging unit to be switched off and the inner pipe connected with the charging unit to be switched on so as to discharge the suspension capacitor.
12. The method of claim 9, wherein if the floating capacitive tri-level Buck circuit includes a current limiting unit, after controlling the floating capacitive tri-level Buck circuit to be connected to an input voltage source, the method further comprises:
controlling a first switch of the current limiting unit to be closed;
and when the difference between the voltage of the floating capacitor and half of the input voltage is reduced to be smaller than a threshold value, a second switch of the current limiting unit is controlled to be closed, and then the step of controlling the inner tube and the outer tube which are connected with the charging unit in the floating capacitor type three-level Buck circuit to be conducted in a staggered mode is executed.
13. The method as claimed in any one of claims 10 to 12, wherein if the inner and outer tubes not connected to the charging unit are field effect transistors MOS, the method further comprises the step of controlling the inner and outer tubes connected to the charging unit in the floating capacitive three-level Buck circuit to be alternately turned on:
controlling two inner tubes and two outer tubes in the suspension capacitance type three-level Buck circuit to be in complementary conduction; or controlling the inner pipe and the outer pipe which are not connected with the charging unit to keep a closed state.
14. A suspended capacitive multilevel bridge circuit, comprising: the device comprises an input capacitor, an output circuit and at least one bridge arm; the bridge arm includes: the capacitive type voltage-reducing circuit comprises a suspension capacitive type n +1 level voltage-reducing conversion unit and n-1 charging units; n is a positive integer greater than 1; wherein:
the positive and negative electrodes of the input end of the suspension capacitance type n +1 level step-down conversion unit are used as the positive and negative electrodes of the input end of the bridge arm and are respectively connected with the two ends of the input capacitor;
the output end of the suspension capacitance type n +1 level buck conversion unit is used as one output end of the bridge arm and is connected with the first end of the output circuit;
the output end of each charging unit is respectively connected with the anode of the corresponding suspension capacitor in the suspension capacitor type n +1 level step-down conversion unit; the input end of each charging unit is respectively connected with any node of the upper bridge arm branch of the floating capacitive type n +1 level buck conversion unit, wherein the voltage of the node is higher than the voltage of a first preset connection point; the voltage of the first preset connection point is the voltage of the connection point of the anode of the corresponding suspension capacitor and the corresponding power tube; alternatively, the first and second electrodes may be,
the input end of each charging unit is respectively connected with the negative electrode of the corresponding suspension capacitor in the suspension capacitor type n +1 level step-down conversion unit; the output end of each charging unit is respectively connected with any node, of which the voltage in the lower bridge arm branch of the floating capacitive type n +1 level buck conversion unit is lower than the voltage of a second preset connection point, of the lower bridge arm branch; the voltage of the second preset connection point is the voltage of the connection point of the negative electrode of the corresponding suspension capacitor and the corresponding power tube;
each charging unit is in a cut-off state after the voltage on the corresponding suspension capacitor is charged to be within a preset range of the corresponding steady-state voltage;
in the suspension capacitance type multi-level bridge circuit, two adjacent power tubes which are connected with the charging unit are conducted in a staggered mode to realize the following steps: charging a corresponding floating capacitor and a corresponding charging unit, charging each floating capacitor and each charging unit, and charging a corresponding charging unit and a corresponding floating capacitor; until the voltage of each suspension capacitor rises to be equal to the corresponding steady-state voltage.
15. The suspended capacitive multilevel bridge circuit of claim 14, wherein each of the charging cells comprises: a balancing capacitor and a charging diode connected in series;
the negative electrode of the balance capacitor is connected with the anode of the charging diode, the positive electrode of the balance capacitor is used as the input end of the charging unit, and the cathode of the charging diode is used as the output end of the charging unit;
alternatively, the first and second electrodes may be,
the anode of the balance capacitor is connected with the cathode of the charging diode, the anode of the charging diode is used as the input end of the charging unit, and the cathode of the balance capacitor is used as the output end of the charging unit.
16. The suspended capacitive multilevel bridge circuit of claim 14, further comprising: a clamp circuit;
the input end of the clamping circuit is connected with the midpoint of the suspended capacitive type n +1 level step-down conversion unit, and the output end of the clamping circuit is connected with the negative electrode of the input end of the suspended capacitive type n +1 level step-down conversion unit;
the clamping circuit maintains the off state when the suspension capacitance type multi-level bridge circuit is in a normal working state, and maintains the on state at other time.
17. The suspended capacitive multilevel bridge circuit of claim 16, wherein the clamp circuit comprises: a clamp capacitor and a third switch connected in series;
the positive electrode of the clamping capacitor is connected with one end of the third switch, the other end of the third switch is used as the input end of the clamping circuit, and the negative electrode of the clamping capacitor is used as the output end of the clamping circuit;
alternatively, the first and second electrodes may be,
the negative electrode of the clamping capacitor is connected with one end of the third switch, the positive electrode of the clamping capacitor is used as the input end of the clamping circuit, and the other end of the third switch is used as the output end of the clamping circuit.
18. The floating capacitance multi-level bridge circuit of claim 17, wherein the capacitance of the clamp capacitor is greater than the capacitance of the balancing capacitor in each of the floating capacitors and each of the charging units, and the difference between the capacitance of the clamp capacitor and the capacitance of each of the floating capacitors and each of the balancing capacitors is greater than a predetermined capacitance.
19. The suspended capacitive multilevel bridge circuit of claim 17, wherein the third switch is any one of a relay, an Insulated Gate Bipolar Transistor (IGBT), and a Metal Oxide Semiconductor Field Effect Transistor (MOSFET).
20. The floating capacitance multi-level bridge circuit of claim 14, wherein when applied to a multi-level Buck circuit:
if each charging unit is connected with the anode of the corresponding floating capacitor, the second end of the output circuit is connected with the cathode of the input end of the floating capacitor type n +1 level step-down conversion unit;
and if each charging unit is respectively connected with the negative electrode of the corresponding suspension capacitor, the second end of the output circuit is connected with the positive electrode of the input end of the suspension capacitor type n +1 level step-down conversion unit.
21. The suspended capacitive multilevel bridge circuit of claim 15, wherein the suspended capacitive n +1 level buck conversion cell comprises: the device comprises an inductor, an upper bridge arm branch, a lower bridge arm branch and n-1 suspension capacitors; wherein:
the upper bridge arm branch and the lower bridge arm branch respectively comprise n power tubes which are sequentially connected in series, and a connection point between every two power tubes is used as a node; the upper bridge arm branch is connected with the lower bridge arm branch, and a connection point is used as a midpoint of the suspension capacitance type n +1 level buck conversion unit;
one end of the inductor is connected with the midpoint, and the other end of the inductor is used as the output end of the suspended capacitive type n +1 level step-down conversion unit;
one end of each suspension capacitor is connected with each node in the upper bridge arm branch in a one-to-one correspondence mode, and the other end of each suspension capacitor is connected with the symmetrical nodes in the lower bridge arm branch in a one-to-one correspondence mode.
22. The suspended capacitive multilevel bridge circuit of claim 21, wherein the bridge arm further comprises: the n-1 discharge units are used for discharging corresponding balance capacitors after the suspension capacitance type multi-level bridge circuit is powered down;
and/or the presence of a gas in the gas,
when the input voltage source accessed by the suspension capacitance type multilevel bridge circuit is a stable input voltage source, the bridge arm further comprises: and the current limiting unit is arranged between the stable input voltage source and the input capacitor and used for limiting the charging current of the parallel parasitic capacitor of the power tube which is not connected with the charging unit and the midpoint when the suspended capacitive multi-level bridge circuit is connected to the input voltage source.
23. The suspended capacitive multilevel bridge circuit of claim 22, wherein each of the discharge cells comprises: a discharge diode;
if at least one charging unit is connected with the anode of the input capacitor, the anode of the discharging diode is respectively connected with the cathode of the input capacitor and the cathode of the input end of the bridge arm, and the cathode of the discharging diode is connected with the cathode of the corresponding balance capacitor;
if at least one charging unit is connected with the negative electrode of the input capacitor, the cathode of the discharging diode is respectively connected with the positive electrode of the input capacitor and the positive electrode of the input end of the bridge arm, and the anode of the discharging diode is connected with the positive electrode of the corresponding balance capacitor;
the current limiting unit includes: the circuit comprises a first switch, a second switch and a current-limiting resistor; the first switch is connected with the current-limiting resistor in series, and a series branch of the first switch and the current-limiting resistor is connected with the second switch in parallel.
24. The floating capacitance type multilevel bridge circuit of any one of claims 21 to 23, wherein each power transistor in the upper bridge arm branch is a diode or a reverse conducting transistor; each power tube in the lower bridge arm branch is a diode or a reverse conducting transistor; each power tube in the upper bridge arm branch and each power tube in the lower bridge arm branch are not diodes at the same time;
if each power tube in the lower bridge arm branch is a diode, each charging unit is connected with the anode of the corresponding suspension capacitor;
and if each power tube in the upper bridge arm branch is a diode, each charging unit is connected with the cathode of the corresponding suspension capacitor.
25. The floating capacitance type multilevel bridge circuit of any of claims 14 to 23, wherein each of the charging units is in a conducting state before the floating capacitance type multilevel bridge circuit enters a normal operating state after being powered on, so that the voltage across the corresponding floating capacitance is charged by each of the charging units to a preset range of a steady-state voltage corresponding to the floating capacitance type multilevel bridge circuit after entering the normal operating state.
26. A method of controlling a floating capacitive multilevel bridge circuit, the method being applied to a controller for a floating capacitive multilevel bridge circuit according to any of claims 14 to 24, the method comprising:
controlling the suspension capacitance type multi-level bridge circuit to be connected to an input voltage source;
and when the difference value between the voltage of each floating capacitor and the corresponding steady-state voltage of the floating capacitor type multi-level bridge circuit after the floating capacitor type multi-level bridge circuit enters a normal working state is reduced to be smaller than a threshold value, controlling two adjacent power tubes in the floating capacitor type multi-level bridge circuit, which are connected with the charging unit, to be in staggered conduction.
27. The method of claim 26, wherein controlling the conduction of two adjacent power transistors of the floating-capacitance-type multi-level bridge circuit, which are connected to a charging unit, alternately comprises:
controlling power tubes which are connected with the charging units and are positioned at odd-numbered positions to be conducted, and controlling power tubes which are connected with the charging units and are positioned at even-numbered positions to be disconnected, and charging corresponding floating capacitors and corresponding charging units in the floating capacitor type multi-level bridge circuit;
controlling each power tube connected with the charging unit to be turned off, and charging each suspension capacitor and each charging unit;
controlling the power tubes which are connected with the charging unit and are positioned at odd numbers to be switched off, and controlling the power tubes which are connected with the charging unit and are positioned at even numbers to be switched on, so as to charge the corresponding charging unit and the corresponding floating capacitor;
and returning to the step of controlling the conduction of the power tube which is in the odd number and is connected with each charging unit and the disconnection of the power tube which is in the even number and is connected with the charging unit, and charging the corresponding floating capacitor and the corresponding charging unit in the floating capacitor type multi-level bridge circuit until the voltage of each floating capacitor rises to be equal to the corresponding steady-state voltage.
28. The method as claimed in claim 26, further comprising the following steps performed in a cycle after the voltage of each floating capacitor rises to equal the corresponding steady-state voltage:
controlling the power tubes which are connected with the charging unit and are positioned at odd numbers to be conducted, and controlling the power tubes which are connected with the charging unit and are positioned at even numbers to be disconnected, so as to charge the corresponding floating capacitors;
controlling each power tube connected with the charging unit to be turned off, so that each suspension capacitor and each charging unit are not charged or discharged;
and controlling the power tube which is connected with the charging unit and is positioned at an odd number position to be switched off, and controlling the power tube which is connected with the charging unit and is positioned at an even number position to be switched on, so as to discharge the corresponding suspension capacitor.
29. The method of claim 26, wherein if the floating capacitive multilevel bridge circuit includes a current limiting unit, after controlling the floating capacitive multilevel bridge circuit to be connected to an input voltage source, the method further comprises:
controlling a first switch of the current limiting unit to be closed;
and when the difference value between the voltage of each floating capacitor and the corresponding steady-state voltage is reduced to be smaller than a threshold value, the second switch of the current limiting unit is controlled to be closed, and then the step of controlling the two adjacent power tubes in the floating capacitor type multi-level bridge circuit, which are connected with the charging unit, to be conducted in a staggered mode is executed.
30. The method as claimed in any one of claims 26 to 29, wherein if each of the power transistors of the floating capacitive multilevel bridge circuit that is not connected to the charging unit is a MOS transistor, the method further comprises controlling two adjacent power transistors of the floating capacitive multilevel bridge circuit that are connected to the charging unit to be turned on alternately:
controlling each power tube in the suspension capacitance type multi-level bridge circuit, which is not connected with the charging unit, to be in complementary conduction with the symmetrical power tube connected with the charging unit; or controlling each power tube which is not connected with the charging unit in the floating capacitance type multi-level bridge circuit to keep an off state.
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