CN115133777B - Isolated DC converter and control method - Google Patents

Isolated DC converter and control method Download PDF

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Publication number
CN115133777B
CN115133777B CN202210871335.5A CN202210871335A CN115133777B CN 115133777 B CN115133777 B CN 115133777B CN 202210871335 A CN202210871335 A CN 202210871335A CN 115133777 B CN115133777 B CN 115133777B
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switching tube
switching
circuit
bridge
isolated
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CN115133777A (en
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张雷
李海东
谷海涛
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Beijing Lei Jing Zhi Chuang Technology Co ltd
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Beijing Lei Jing Zhi Chuang Technology 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
    • H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
    • H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
    • H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
    • H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
    • H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/33569—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements
    • 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
    • H02M1/0048—Circuits or arrangements for reducing losses
    • H02M1/0054—Transistor switching losses
    • H02M1/0058—Transistor switching losses by employing soft switching techniques, i.e. commutation of transistors when applied voltage is zero or when current flow is zero
    • 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
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
    • Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/56—Power conversion systems, e.g. maximum power point trackers

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Dc-Dc Converters (AREA)

Abstract

The invention discloses an isolated DC converter and a control method, wherein the isolated DC converter comprises: the three-level Boost circuit comprises a plurality of three-level Boost circuits, a first resonance soft switching module, a second resonance soft switching module, a first contactor, a second contactor, an output EMI filter and a central control unit. The control method comprises the following steps: acquiring output current and output voltage of each Boost circuit to control the power or the output voltage of the Boost circuit; the method comprises the steps of obtaining primary side current and secondary side output voltage values of a first resonance soft switching module and a second resonance soft switching module, controlling output voltage or output power, and realizing zero voltage switching-on of the first resonance soft switching module and the second resonance soft switching module by selecting proper resonance frequency. The isolated DC converter can be used for DC power transmission in a photovoltaic power generation system and hydrogen production by electrolyzing water in photovoltaic power generation.

Description

Isolated DC converter and control method
Technical Field
The invention belongs to the field of photovoltaic power generation and transmission, and particularly relates to an isolated direct current converter and a control method.
Background
Photovoltaic power generation is an important power generation form in a renewable energy power generation system, at present, photovoltaic power generation is mainly converted by an inverter and is merged into an alternating current power grid, the photovoltaic voltage level is low and is generally below 1500V, so that the cable cost of a photovoltaic power station is high, and the cable loss is also high. The cost of the cable can be reduced by improving the transmission voltage grade, but the cable is limited by the problem of voltage resistance of a photovoltaic module, and few photovoltaic direct-current transmission systems with voltage exceeding 1500V exist at present.
Most of the mainstream DC-DC converters in the field of photovoltaic power generation are non-isolated equipment, and if the voltage of an output end exceeds the withstand voltage value of a photovoltaic module, the photovoltaic module can be damaged under the condition of short circuit to the ground, and even a fire disaster is caused.
Patent CN110838794A discloses a topological circuit of a series-connection type photovoltaic high-voltage direct-current grid-connected converter and a modulation method, an isolation type DC-DC conversion topology is adopted, but the output voltage is adjusted by changing the duty ratio, the duty ratio is not fixed 50%, the utilization rate of an isolation transformer is limited, and the efficiency is low in a voltage reduction mode; the input side does not adopt a multi-path MPPT circuit, but integrates the MPPT function into a main circuit, so that the power generation efficiency of a photovoltaic module is limited; in addition, the voltage borne by the topological switch tube is bus voltage and is limited by the withstand voltage of a switch device, and the topological structure is only suitable for photovoltaic power generation systems of 1000V or below.
Disclosure of Invention
The present invention is directed to an isolated dc converter and a control method thereof, so as to solve the above problems of the prior art.
To achieve the above object, the present invention provides an isolated dc converter, including: the three-level Boost circuit comprises a three-level Boost circuit, a first resonance soft switching module, a second resonance soft switching module, a first contactor, a second contactor, an output EMI filter and a central control unit;
the first resonant soft switch module comprises a first H-bridge circuit, a first series resonant cavity and a first rectifying circuit; the first H-bridge circuit is connected with the first series resonant cavity;
the second resonant soft switch module comprises a second H-bridge circuit, a second series resonant cavity and a second rectifying circuit; the second H-bridge circuit is connected with the second series resonant cavity;
the three-level Boost circuit is connected with the first H bridge circuit and the second H bridge circuit;
the first contactor is connected with the first rectifying circuit, and the second contactor is connected with the second rectifying circuit;
the output EMI filter is respectively connected with the three-level Boost circuit;
the central control unit is connected with the three-level Boost circuit, the first resonant soft switch module and the second resonant soft switch module.
Preferably, the first H-bridge circuit includes a first switch tube, a second switch tube, a third switch tube, and a fourth switch tube; the first switching tube and the second switching tube are connected to form a first bridge arm, and the third switching tube and the fourth switching tube are connected to form a second bridge arm; the first bridge arm and the second bridge arm are respectively connected with two ends of the first series resonant cavity;
the second H-bridge circuit comprises a fifth switching tube, a sixth switching tube, a seventh switching tube and an eighth switching tube; the fifth switching tube and the sixth switching tube are connected to form a third bridge arm, and the seventh switching tube and the eighth switching tube are connected to form a fourth bridge arm; and the third bridge arm and the fourth bridge arm are respectively connected with two ends of the second resonant cavity.
Preferably, the first series resonant cavity comprises a first resonant inductor, a first resonant capacitor and a first isolation transformer which are connected in sequence;
the second series resonant cavity comprises a second resonant inductor, a second resonant capacitor and a second isolation transformer which are sequentially connected.
Preferably, the central control unit is configured to control on and off of switching tubes corresponding to the three-level Boost circuit, the first H-bridge circuit, and the second H-bridge circuit, and obtain a current and a voltage of the three-level Boost circuit, a current of the first series resonant cavity and the second series resonant cavity, and a voltage of the first rectifying circuit and the second rectifying circuit.
The invention also provides a control method of the isolated DC converter, which comprises the following steps:
adjusting the output voltage or the output power of the three-level Boost circuit based on the control mode of the three-level Boost circuit;
based on voltage stabilization and frequency limitation control, presetting an oscillation frequency lower limit at the same time, and acquiring a switching frequency corresponding to a switching tube;
and controlling the switching tubes corresponding to the first H-bridge circuit and the second H-bridge circuit to work and controlling the zero-voltage switching-on soft switch to operate based on the switching frequency corresponding to the switching tubes.
Preferably, the process of adjusting the output voltage or the output power of the three-level Boost circuit based on the control mode of the three-level Boost circuit includes:
based on a maximum power tracking control mode, all three-level Boost circuits change output voltage at regular time to obtain different output powers; obtaining a maximum power point based on the different output powers;
based on a voltage-stabilizing control mode, all three-level Boost circuits control output voltage by adjusting duty ratio based on a preset voltage droop curve.
Preferably, the process of acquiring the switching frequency corresponding to the switching tube includes:
based on the first PI regulator, performing difference processing on a first target output voltage and a first actual output voltage of the first rectifying circuit to obtain a first target oscillation frequency value; the first target oscillation frequency value is not less than a preset oscillation frequency lower limit value; controlling the first series resonant cavity to work based on the first target oscillation frequency value; the first target oscillation frequency value is the switching frequency of the first H-bridge switching tube;
based on a second PI regulator, performing difference processing on a second target output voltage and a second actual output voltage of a second rectifying circuit to obtain a second target oscillation frequency value; the first target oscillation frequency value is not less than a preset oscillation frequency lower limit value; controlling a second series resonant cavity to work based on the second target oscillation frequency value; and the second target oscillation frequency value is the switching frequency of the second H-bridge switching tube.
Preferably, the process of controlling the operation of the switching tubes corresponding to the first H-bridge circuit and the second H-bridge circuit further includes:
a first switching tube and a fourth switching tube of a first H-bridge circuit, a second switching tube and a third switching tube are synchronously switched on, wherein the switching-on moments of the first switching tube and the second switching tube of the first H-bridge circuit are complementary; and controlling a fifth switching tube and an eighth switching tube, a sixth switching tube and a seventh switching tube of the second H-bridge circuit to be synchronously switched on, wherein the switching-on moments of the fifth switching tube and the sixth switching tube of the second H-bridge circuit are complementary.
The invention has the technical effects that:
according to the invention, the first resonant soft switch module and the second resonant soft switch module are constructed, and a voltage-stabilizing frequency-limiting soft switch control method is adopted, so that high-efficiency voltage grade conversion is realized.
The isolated DC converter provided by the invention can be used for DC power transmission in a photovoltaic power generation system and hydrogen production by electrolyzing water in photovoltaic power generation.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the application and, together with the description, serve to explain the application and are not intended to limit the application. In the drawings:
fig. 1 is a schematic circuit diagram of an isolated dc converter according to an embodiment of the present invention;
101-a first path of three-level Boost circuit, 102-a second path of three-level Boost circuit, 103-an Nth path of three-level Boost circuit, 104-a first resonant soft switching module, 105-a second resonant soft switching module, K21-a first contactor, K22-a second contactor, 106-an output EMI filter, 107-a central control unit, 108-a first photovoltaic assembly, 109-a second photovoltaic assembly, 110-a third photovoltaic assembly and 111-an EMI filter;
fig. 2 is a control flowchart of the isolated dc converter according to the embodiment of the present invention;
FIG. 3 is an exemplary schematic diagram of an isolated DC converter used for high voltage transmission in a photovoltaic system according to an embodiment of the present invention;
301-a photovoltaic component, 302-a multi-path Boost circuit of a first isolated direct current converter, 303-a first resonant soft switching module of the first isolated direct current converter, 304-a second resonant soft switching module of the first isolated direct current converter, 305-a multi-path Boost circuit of an Nth isolated direct current converter, 306-a first resonant soft switching module of the Nth isolated direct current converter, 307-a second resonant soft switching module of the Nth isolated direct current converter, 308-an inverter and 309-a transformer;
FIG. 4 is a schematic diagram illustrating an exemplary principle of an isolated DC converter for hydrogen production by photovoltaic electrolysis of water according to an embodiment of the present invention;
the photovoltaic module is 401-a photovoltaic module, 402-a multi-path Boost circuit of a first isolation type direct current converter, 403-a first resonance soft switching module of the first isolation type direct current converter, 404-a second resonance soft switching module of the first isolation type direct current converter, 405-a multi-path Boost circuit of an Nth isolation type direct current converter, 406-a first resonance soft switching module of the Nth isolation type direct current converter, 407-a first resonance soft switching module of the Nth isolation type direct current converter and 408-an electrolytic cell load.
Detailed Description
It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict. The present application will be described in detail below with reference to the accompanying drawings in conjunction with embodiments.
It should be noted that the steps shown in the flow chart of the figure may be performed in a computer system such as a Digital Signal Processor (DSP), a single chip, etc. that can execute instructions, and that while a logical order is shown in the flow chart, in some cases the steps shown or described may be performed in an order different than here.
Example one
As shown in fig. 1 to 4, the present embodiment provides an isolated dc converter, including: the three-level Boost circuit comprises a plurality of three-level Boost circuits, a first resonance soft switching module, a second resonance soft switching module, a first contactor, a second contactor, an output EMI filter and a central control unit;
the first resonant soft switch module comprises a first H-bridge circuit, a first series resonant cavity and a first rectifying circuit; the first H-bridge circuit is connected with the first series resonant cavity;
the second resonant soft switch module comprises a second H-bridge circuit, a second series resonant cavity and a second rectifying circuit; the second H-bridge circuit is connected with the second series resonant cavity;
the input end of each three-level Boost circuit is provided with a direct-current isolating switch, an EMI filter and a group of bypass diodes, the outputs of all the Boost circuits are connected in parallel, the output anode is connected with the anode of the first H-bridge circuit, and the output cathode is connected with the cathode of the second H-bridge circuit; the first H-bridge circuit is connected with the second H-bridge circuit in series; each circuit of the three-level Boost circuit is provided with 4 switching tubes and 2 bypass diodes, and the 2 bypass diodes are respectively placed on the anode and the cathode and are connected in parallel with a circuit formed by the inductor and the follow current switching tubes.
The first contactor is connected with the first rectifying circuit, and the second contactor is connected with the second rectifying circuit; the first rectifying circuit is composed of a rectifying bridge and a filter capacitor which are composed of 4 diodes, and the second rectifying circuit is composed of a rectifying bridge and a filter capacitor which are composed of 4 diodes; alternatively, the diode may be replaced by a controllable switching tube, such as a MOSFET.
And the central control unit is connected with the three-level Boost circuit, the first resonance soft switch module and the second resonance soft switch module.
The first H-bridge circuit comprises 4 switching tubes, wherein the switching tubes are respectively Q1, Q2, Q3 and Q4, the Q1 and the Q2 are connected in series to form one bridge arm, and the Q3 and the Q4 are connected in series to form the other bridge arm; the second H-bridge circuit comprises 4 switching tubes which are respectively Q5, Q6, Q7 and Q8, wherein the Q5 and the Q6 are connected in series to form one bridge arm, and the Q7 and the Q8 form the other bridge arm; the middle points of 2 bridge arms of the first H-bridge circuit are respectively connected with two ends of the first series resonant cavity, and the middle points of 2 bridge arms of the second H-bridge circuit are respectively connected with two ends of the second resonant cavity.
The first series resonant cavity comprises a first resonant inductor, a first resonant capacitor and a first isolation transformer which are sequentially connected; the second series resonant cavity comprises a second resonant inductor, a second resonant capacitor and a second isolation transformer which are connected in sequence.
The central control unit is used for controlling the on-off of the switching tubes in the Boost circuit, controlling the on-off of the switching tubes in the first H-bridge circuit and the second H-bridge circuit, obtaining the output current, the input voltage and the output voltage of the Boost circuit, and collecting the currents of the first series resonant cavity and the second series resonant cavity; and acquiring output voltages of the first rectifying circuit and the second rectifying circuit.
In order to achieve the above object, this embodiment further provides a method for controlling an isolated dc converter, including the following steps:
adjusting the output voltage or the output power of the three-level Boost circuit based on the control mode of the three-level Boost circuit;
on the basis of voltage-stabilizing frequency-limiting control and preset duty ratio, controlling the switching tubes corresponding to the first H-bridge circuit and the second H-bridge circuit to work;
and acquiring the switching frequency corresponding to the switching tube, and controlling the zero-voltage switching-on soft switch to operate based on the switching frequency.
The control method of the three-level Boost circuit comprises a Maximum Power Point Tracking (MPPT) control mode and a voltage stabilization control mode 2, wherein in the MPPT control mode, all three-level Boost circuits automatically change output voltage at regular time to further influence input side voltage, the change of input voltage and output current can cause the change of output power, and a maximum power point is sought through the change of the output power; in the voltage stabilization control mode, all three-level Boost circuits take a preset voltage droop curve as a control target, and output voltage is controlled by adjusting duty ratio; in any mode, the switching timing in all three-level Boost circuits is phase-shift interleaved.
When the input voltage reaches the voltage value that the first resonance soft switch module and the second resonance soft switch module can normally operate, the control method of the three-level Boost circuit is that the Boost inductor in the control circuit is bypassed to improve the efficiency, the bypass of the Boost inductor is realized by controlling 2 switch tubes in 4 switch tubes in charge of energy storage to be switched off, and 2 switch tubes in charge of follow current are switched on at the same time, and the Boost control is not performed at the moment.
The process of controlling the operation of the switching tubes corresponding to the first H-bridge circuit and the second H-bridge circuit may include:
voltage stabilization and frequency limitation control are carried out, meanwhile, the first H bridge circuit Q1 and the first H bridge circuit Q4 are controlled to be synchronously switched on, the first H bridge circuit Q2 and the second H bridge circuit Q3 are synchronously switched on, and the switching-on moments of the first H bridge circuit Q1 and the second H bridge circuit Q2 are complementary; the second H-bridge circuit Q5 and Q8 are synchronously switched on, Q6 and Q7 are synchronously switched on, and the switching-on time of Q5 is complementary with that of Q6; the duty ratio of all the switching tubes of the first H-bridge circuit and the second H-bridge circuit is 50%, and the zero-voltage switching-on soft switching operation is realized by selecting a proper switching frequency section of the switching tubes.
The voltage-stabilizing frequency-limiting control process comprises the following steps: acquiring corresponding control targets based on output voltages corresponding to the first rectifying circuit and the second rectifying circuit; and adjusting the output voltage by changing the oscillation frequency of the first series resonant cavity and the second series resonant cavity based on the control target.
The process of acquiring the switching frequency corresponding to the switching tube may include:
the difference between the target voltage and the actual voltage of the first rectifying circuit enters a first PI regulator to obtain a target oscillation frequency value, and the frequency value is used as the switching frequency of a first H-bridge switching tube to control the first series resonant cavity to work; and the difference between the target voltage and the actual voltage of the second rectifying circuit enters a second PI regulator to obtain a target oscillation frequency value, and the frequency value is used as the switching frequency of a second H-bridge switching tube to control the second series resonant cavity to work.
The control link using the voltage as the control target also adds the limitation of the oscillation frequency, and a minimum oscillation frequency is given, so that the frequency cannot be lower than the set minimum oscillation frequency even if the output voltage does not reach the target voltage value.
Example two
As shown in fig. 1, the isolated dc converter proposed in this embodiment includes a multi-path three-level Boost circuit: the circuit comprises a first three-level Boost circuit 101, a second three-level Boost circuit 102 …, an Nth three-level Boost circuit 103, a first resonant soft switch module 104, a second resonant soft switch module 105, a first contactor K21, a second contactor K22, an output EMI filter 106, a central control unit 107, a first photovoltaic module 108, a second photovoltaic module 109, a third photovoltaic module 110 and an EMI filter 111.
The input ends of the three-level Boost circuits are respectively connected with the photovoltaic cell components, and the outputs are connected in parallel. The internal circuits of all the Boost circuits are the same, and the Boost circuit comprises a direct current switch K11, wherein K11 is connected with an external photocell assembly 107, the other end of K11 is connected with the input end of an EMI filter 111, an input filter capacitor Ci1 is connected in parallel with the output end of the EMI filter 111, the positive pole of the filter capacitor Ci1 is connected with a positive pole Boost inductor L11, the negative pole of the filter capacitor Ci1 is connected with a negative pole Boost inductor L12, the other end of the positive pole Boost inductor L11 is connected with the connection point of a positive pole freewheeling switch tube Q11 and a switch tube Q12, and the negative pole Boost inductor L12 is connected with the connection point of a negative pole freewheeling switch tube Q14 and a switch tube Q13. An output anode filter capacitor C11 and a cathode filter capacitor C12 are connected in series and then connected to the output end of the three-level Boost circuit in parallel, the anode of a first bypass diode D11 is connected with the anode of an input filter capacitor Ci1, and the cathode of the D11 is connected with the anode of the output anode filter capacitor C11; the cathode of the second bypass diode D12 is connected with the cathode of the input filter capacitor Ci1, and the anode of the D11 is connected with the cathode of the output cathode filter capacitor C11.
The first resonant soft switch module 104 is composed of a first H-bridge circuit, a first series resonant cavity, and a first rectifying circuit; the second resonant soft switching module 105 is composed of a second H-bridge circuit, a second series resonant cavity, and a second rectifying circuit.
The first H-bridge circuit comprises 4 switching tubes, namely Q1, Q2, Q3 and Q4, wherein the Q1 and the Q2 are connected in series to form one bridge arm, and the Q3 and the Q4 are connected in series to form the other bridge arm; the second H-bridge circuit comprises 4 switching tubes which are Q5, Q6, Q7 and Q8 respectively, wherein the Q5 and the Q6 are connected in series to form one bridge arm, and the Q7 and the Q8 form the other bridge arm.
The first resonant cavity is formed by connecting a first resonant inductor L1, a first resonant capacitor C3 and the primary side of a first isolation transformer T1 in series, and the second resonant cavity is formed by connecting a second resonant inductor L2, a second resonant capacitor C4 and the primary side of a second isolation transformer T2 in series.
The middle points of 2 bridge arms of the first H-bridge circuit are respectively connected with two ends of the first series resonant cavity, and the middle points of 2 bridge arms of the second H-bridge circuit are respectively connected with two ends of the second resonant cavity.
The first rectification circuit consists of a rectification bridge consisting of 4 diodes D1, D2, D3 and D4 and a filter capacitor C21; the second rectifying circuit is composed of a rectifying bridge composed of 4 diodes D5, D6, D7 and D8 and a filter capacitor C22.
Alternatively, the diodes D1, D2, D3, D4, D5, D6, D7, D8 may be replaced with MOSFETs.
The first contactor K21 is connected in series to the output end of the first rectifying circuit, and the second contactor K22 is connected in series to the output end of the second rectifying circuit.
The central control unit 107 is configured to control on and off of switching tubes in the Boost circuit, control on and off of switching tubes in the first H-bridge circuit and the second H-bridge circuit, obtain an output current, an input voltage, and an output voltage of the Boost circuit, and collect currents of the first series resonant cavity and the second series resonant cavity; and collecting output voltages of the first rectifying circuit and the second rectifying circuit.
The control flow of the isolated dc converter provided in this embodiment is shown in fig. 2, and these controls are executed in the central control unit.
Specifically, in step 201, an output current, an input voltage, and an output voltage value of each three-level Boost circuit are respectively obtained, and a first resonant cavity current value, a second resonant cavity current value, and a first rectifying circuit output voltage, and a second rectifying circuit output voltage are obtained.
In step 202, the control mode is determined, and if the current mode is the Maximum Power Point Tracking (MPPT) mode, the step 203 is skipped, otherwise, the step 204 is skipped.
In step 203, an MPPT control mode is executed, all three-level Boost circuits automatically and regularly change output voltage to influence input-side voltage, the change of input voltage and output current can cause the change of output power, and the maximum power point is sought through the change of output power.
In step 204, a voltage stabilization control mode is executed, all the three-level Boost circuits take preset voltage droop curves as control targets, and output voltage is controlled by adjusting duty ratios.
In any mode, the switching timing in all three-level Boost circuits is phase-shift interleaved.
In step 205, a first resonant cavity control is executed, the output voltage of the first rectifying circuit is used as a control target, a target oscillation frequency value of the first H-bridge circuit is calculated through the PI regulator, and the oscillation frequency is limited during the control, wherein the resonance frequency is not less than a preset lower limit value of the resonance frequency. The system presets a minimum oscillation frequency, which is not lower than the set minimum oscillation frequency even if the output voltage does not reach the target voltage value.
In step 206, a second resonant cavity control is executed, the output voltage of the second rectifying circuit is used as a control target, a target oscillation frequency value of the second H-bridge circuit is calculated through the PI regulator, and the oscillation frequency is limited during the control, wherein the resonance frequency is not less than a preset lower limit value of the resonance frequency. The system presets a minimum oscillation frequency, which is not lower than the set minimum oscillation frequency even if the output voltage does not reach the target voltage value.
In step 207, the first H-bridge circuit and the second H-bridge circuit are controlled according to the switching frequency values obtained in steps 205 and 206, respectively. The first H-bridge circuit Q1 and Q4 are synchronously switched on, Q2 and Q3 are synchronously switched on, the switching moments of Q1 and Q2 are complementary, the duty ratios of the switching tubes Q1, Q4, Q2 and Q3 are 50%, and zero-voltage switching-on soft switching operation is realized; the second H-bridge circuit Q5 and Q8 are synchronously switched on, Q6 and Q7 are synchronously switched on, the switching moments of Q5 and Q6 are complementary, the duty ratios of the switching tubes Q5, Q6, Q7 and Q8 are 50%, and the zero-voltage switching-on soft switching operation is realized.
An exemplary principle of the isolated dc converter provided in this embodiment for high-voltage power transmission of a photovoltaic system is shown in fig. 3. In fig. 3, 301 represents a photovoltaic module, 302 represents a multi-path Boost circuit of a first isolated dc converter, 303 represents a first resonant soft switching module of a first isolated dc converter, 304 represents a second resonant soft switching module of the first isolated dc converter, 305 represents a multi-path Boost circuit of an nth isolated dc converter, 306 represents a first resonant soft switching module of an nth isolated dc converter, 307 represents a second resonant soft switching module of the nth isolated dc converter, 308 represents an inverter, and 309 represents a transformer. The photovoltaic module 301 serves as an input of the isolated dc converter provided in this embodiment, and connects output terminals of the dc converters in series. In fig. 3, a first resonant soft switching module 303 and a second resonant soft switching module 304 of a first isolated dc conversion are connected in series; the first resonant soft switch module 306 and the second resonant soft switch module 307 of the N (N is more than or equal to 2) isolation type direct current converter are connected in series and then are connected in series with other isolation type direct current converters, and the output ends of the first resonant soft switch module and the second resonant soft switch module are connected in series to obtain direct current with higher voltage level. The cable cost and the cable loss can be greatly reduced by high-voltage direct current power transmission, the power is inverted into alternating current through the inverter 308 after being transmitted for a certain distance, and the alternating current is boosted or reduced through the transformer 309 and then is connected to a power grid.
In the photovoltaic power transmission system, the number of the isolated dc converters may be 1, or may be plural.
An exemplary principle of the isolated dc converter for hydrogen production by photovoltaic electrolyzed water provided by this embodiment is shown in fig. 4, and in fig. 4, 401 — a photovoltaic module, 402 — a multi-way Boost circuit of a first isolated dc converter, 403 — a first resonant soft switch module of the first isolated dc converter, 404 — a second resonant soft switch module of the first isolated dc converter, 405 — a multi-way Boost circuit of an nth isolated dc converter, 406 — a first resonant soft switch module of the nth isolated dc converter, 407 — a first resonant soft switch module of the nth isolated dc converter, and 408-an electrolytic bath load. The input of the multi-path Boost circuit 402 of the first isolated dc converter in fig. 4 is connected to the photovoltaic module, and the output of the first resonant soft switching module 403 is connected in parallel with the output of the second resonant soft switching module. The system comprises one or more isolated DC converters, an Nth multi-path Boost circuit 405, an Nth output of the first resonant soft switch module 403 in parallel connection with an output of the second resonant soft switch module 404, an output end of the first isolated DC converter is connected in parallel, output current is increased through multi-path parallel connection, and the multi-path parallel connection is connected to an electrolytic cell load 408.
In the above photovoltaic power generation hydrogen production system, the multi-path Boost circuit 402 may be separated from the first resonant soft-switching module 403 and the second resonant soft-switching module 404, the multi-path Boost circuit 402 is installed near the photovoltaic module, and the first resonant soft-switching module 403 and the second resonant soft-switching module may be installed near the hydrogen production electrolytic cell.
The above description is only for the preferred embodiment of the present application, but the scope of the present application is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present application should be covered within the scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims (7)

1. A control method for an isolated direct current converter is characterized by comprising the following steps:
adjusting the output voltage or the output power of the three-level Boost circuit based on the control mode of the three-level Boost circuit;
based on voltage stabilization and frequency limitation control, presetting an oscillation frequency lower limit at the same time, and acquiring a switching frequency corresponding to a switching tube;
on the basis of the switching frequency corresponding to the switching tubes, the switching tubes corresponding to the first H-bridge circuit and the second H-bridge circuit are controlled to work, and the zero-voltage switching-on soft switch is controlled to operate;
the isolated DC converter includes: the three-level Boost circuit comprises a three-level Boost circuit, a first resonance soft switching module, a second resonance soft switching module, a first contactor, a second contactor, an output EMI filter and a central control unit;
the first resonant soft switch module comprises a first H-bridge circuit, a first series resonant cavity and a first rectifying circuit; the first H-bridge circuit is connected with the first series resonant cavity;
the second resonant soft switch module comprises a second H-bridge circuit, a second series resonant cavity and a second rectifying circuit; the second H-bridge circuit is connected with the second series resonant cavity;
the three-level Boost circuit is connected with the first H bridge circuit and the second H bridge circuit;
the first contactor is connected with the first rectifying circuit, and the second contactor is connected with the second rectifying circuit;
the output EMI filter is respectively connected with the three-level Boost circuit;
the central control unit is connected with the three-level Boost circuit, the first resonance soft switch module and the second resonance soft switch module.
2. The isolated DC converter control method according to claim 1,
the first H-bridge circuit comprises a first switching tube, a second switching tube, a third switching tube and a fourth switching tube; the first switching tube and the second switching tube are connected to form a first bridge arm, and the third switching tube and the fourth switching tube are connected to form a second bridge arm; the first bridge arm and the second bridge arm are respectively connected with two ends of the first series resonant cavity;
the second H-bridge circuit comprises a fifth switching tube, a sixth switching tube, a seventh switching tube and an eighth switching tube; the fifth switching tube and the sixth switching tube are connected to form a third bridge arm, and the seventh switching tube and the eighth switching tube are connected to form a fourth bridge arm; and the third bridge arm and the fourth bridge arm are respectively connected with two ends of the second series resonant cavity.
3. The isolated DC converter control method according to claim 1,
the first series resonant cavity comprises a first resonant inductor, a first resonant capacitor and a first isolation transformer which are sequentially connected;
the second series resonant cavity comprises a second resonant inductor, a second resonant capacitor and a second isolation transformer which are sequentially connected.
4. The isolated DC converter control method according to claim 1,
the central control unit is used for controlling the on-off of the switching tubes corresponding to the three-level Boost circuit, the first H-bridge circuit and the second H-bridge circuit, and obtaining the current and the voltage of the three-level Boost circuit, the current of the first series resonant cavity and the second series resonant cavity and the voltage of the first rectifying circuit and the second rectifying circuit.
5. The isolated DC converter control method according to claim 1,
based on the control mode of the three-level Boost circuit, the process of adjusting the output voltage or the output power of the three-level Boost circuit comprises the following steps:
based on a maximum power tracking control mode, all three-level Boost circuits change output voltage at regular time to obtain different output powers; obtaining a maximum power point based on the different output powers;
based on a voltage-stabilizing control mode, all three-level Boost circuits control output voltage by adjusting duty ratio based on a preset voltage droop curve.
6. The isolated DC converter control method according to claim 1,
the process of acquiring the switching frequency corresponding to the switching tube comprises the following steps:
based on the first PI regulator, performing difference processing on a first target output voltage and a first actual output voltage of the first rectifying circuit to obtain a first target oscillation frequency value; the first target oscillation frequency value is not less than a preset oscillation frequency lower limit value; controlling the first series resonant cavity to work based on the first target oscillation frequency value; the first target oscillation frequency value is the switching frequency of the first H-bridge switching tube;
based on a second PI regulator, performing difference processing on a second target output voltage and a second actual output voltage of a second rectifying circuit to obtain a second target oscillation frequency value; the second target oscillation frequency value is not less than a preset oscillation frequency lower limit value; controlling a second series resonant cavity to work based on the second target oscillation frequency value; and the second target oscillation frequency value is the switching frequency of the second H-bridge switching tube.
7. The isolated DC converter control method according to claim 1,
the process of controlling the work of the switching tubes corresponding to the first H-bridge circuit and the second H-bridge circuit further comprises the following steps:
a first switching tube and a fourth switching tube of a first H-bridge circuit, and a second switching tube and a third switching tube are synchronously switched on, wherein the switching-on moments of the first switching tube and the second switching tube of the first H-bridge circuit are complementary; the fifth switching tube and the eighth switching tube, the sixth switching tube and the seventh switching tube of the second H-bridge circuit are controlled to be synchronously switched on, and the switching-on moments of a fifth switching tube and a sixth switching tube of the second H-bridge circuit are complementary.
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