CN111817551A

CN111817551A - Low EMI three-level DC converter

Info

Publication number: CN111817551A
Application number: CN202010486560.8A
Authority: CN
Inventors: 汪洪亮; 田子翔; 朱晓楠; 岳秀梅; 罗安
Original assignee: Hunan University
Current assignee: Hunan University
Priority date: 2020-06-01
Filing date: 2020-06-01
Publication date: 2020-10-23

Abstract

The invention provides a low EMI three-level DC converter, and relates to the technical field of power electronics. In the invention, the low EMI three-level DC converter comprises a low EMI boosting three-level DC converter and a low EMI dropping three-level DC converter. The low-EMI boosting type three-level direct current converter enables the potential on the connecting end of the second follow current circuit and the energy storage circuit to be always higher than the potential on the connecting end of the first follow current circuit and the energy storage circuit through the three-level circuit module, and therefore the output voltage is higher than the input voltage. The low-EMI voltage-reducing type three-level direct current converter enables the potential on the connecting end of the first follow current circuit and the energy storage circuit to be always lower than the potential on the connecting end of the second follow current circuit and the energy storage circuit through the control of the three-level circuit module, and output voltage is lower than input voltage. In the low-EMI boost-type and buck-type three-level direct current converters, the current of the input side and the current of the output side are continuous in the whole control process, so that the EMI noise of a power supply is reduced.

Description

Low EMI three-level DC converter

Technical Field

The invention relates to the technical field of power electronics, in particular to a low EMI three-level direct current converter.

Background

Compared with a linear power supply, the switching power supply has the advantages of small size, high efficiency and the like, but the output current ripple is large, so that the switching power supply cannot be applied to occasions with high requirements on power supply quality of the power supply, and the development of the switching power supply is severely limited.

The direct current converter formed by the traditional non-isolated boost topology and the traditional buck topology cannot ensure the continuity of the current of the input side and the output side, so that the EMI noise of the power supply is large.

Disclosure of Invention

Technical problem to be solved

Aiming at the defects of the prior art, the invention provides a low-EMI three-level direct current converter, which solves the technical problem that the direct current converter formed by the traditional non-isolated step-up and step-down topologies cannot ensure the continuity of the currents of the input side and the output side, realizes the continuity of the currents and further reduces the EMI noise.

(II) technical scheme

In order to achieve the purpose, the invention is realized by the following technical scheme:

in a first aspect, the present invention provides a low EMI three-level dc converter unit having four connection terminals including a first connection terminal, a second connection terminal, a third connection terminal and a fourth connection terminal, comprising: the circuit comprises a first follow current circuit, a second follow current circuit, an energy storage circuit and a three-level circuit module; wherein the content of the first and second substances,

the first connection end is connected to the second connection end sequentially through the second follow current circuit, the energy storage circuit and the first follow current circuit;

the fourth connecting end is connected with the connecting end of the first follow current circuit and the second connecting end;

the three-level circuit module comprises a first end, a second end and a third end, and the first end is connected with the third connecting end; the second end is connected to the connection end of the first freewheeling circuit and the energy storage circuit; the third end is connected with the connecting end of the energy storage circuit and the second follow current circuit;

the three-level circuit module is connected with a plurality of control ends and is suitable for controlling the electric potentials of two end points, namely, the connecting end of the second follow current circuit and the energy storage circuit and the connecting end of the first follow current circuit and the energy storage circuit under the control of a control signal accessed by the control ends, so that the electric potential of the connecting end of the second follow current circuit and the energy storage circuit is always higher than the electric potential of the connecting end of the first follow current circuit and the energy storage circuit, and in the whole control process, the currents flowing through the four connecting ends, namely, the first connecting end, the second connecting end, the third connecting end and the fourth connecting end, are continuous.

Preferably, the three-level circuit module includes: a first switch circuit, a second switch circuit, a clamping circuit, a first one-way conduction circuit and a second one-way conduction circuit,

the third connecting end is connected to the connecting end of the first follow current circuit and the energy storage circuit through the second switch circuit and the first switch circuit in sequence;

the third connecting end is connected to the connecting end of the energy storage circuit and the second follow current circuit through the second unidirectional conduction circuit and the first unidirectional conduction circuit in sequence;

the connecting end of the second unidirectional conducting circuit and the first unidirectional conducting circuit is connected to the connecting end of the second switch circuit and the first switch circuit through a clamping circuit;

the three-level circuit module provides four working modes under the control of a control signal accessed by a control end of the three-level circuit module, so that the potential at the connecting end of the second follow current circuit and the energy storage circuit is always higher than the potential at the connecting end of the first follow current circuit and the energy storage circuit, and the currents flowing through the four connecting ends, namely the first connecting end, the second connecting end, the third connecting end and the fourth connecting end, are continuous in the whole control process;

the four working modes include:

under the working mode 1: only the first end and the second end of the three-level circuit module are conducted through the second switch circuit and the first switch circuit, and the other ends and ends of the three-level circuit module are disconnected;

under the working mode 2: only the first end of the three-level circuit module is conducted to the second end of the three-level circuit module in a unidirectional mode through the second unidirectional conducting circuit, the clamping circuit and the first switch circuit in sequence, and the other ends and the ends of the three-level circuit module are disconnected;

under the working mode 3: conducting the first end of the three-level circuit module to the third end of the three-level circuit module through the second switch circuit, the clamping circuit and the first unidirectional conducting circuit in sequence in a unidirectional manner, and disconnecting the other ends of the three-level circuit module from the end;

working mode 4 is as follows: and only conducting the first end of the three-level circuit module to the third end of the three-level circuit module in a unidirectional way through a second unidirectional conducting circuit and a first unidirectional conducting circuit in sequence, and disconnecting the other ends of the three-level circuit module from the end.

Preferably, the first switch circuit at least comprises a first switch, a first end of the first switch is connected with the second switch circuit, and a second end of the first switch is connected with the connection end of the first free-wheeling circuit and the energy storage circuit;

and/or the presence of a gas in the gas,

the second switch circuit at least comprises a second switch, the first end of the second switch is connected with the third connecting end, and the second end of the second switch is connected with the first switch circuit;

and/or the presence of a gas in the gas,

the clamping circuit at least comprises a clamping capacitor, one end of the clamping capacitor is connected to the connecting end of the second unidirectional conducting circuit and the first unidirectional conducting circuit, and the other end of the clamping capacitor is connected to the connecting end of the first switch circuit and the second switch circuit;

and/or the presence of a gas in the gas,

the first unidirectional conduction circuit at least comprises a first diode, the anode of the first diode is connected with the second unidirectional conduction circuit, and the cathode of the first diode is connected with the connecting end of the energy storage circuit and the second follow current circuit;

and/or the presence of a gas in the gas,

the second unidirectional conduction circuit at least comprises a second diode, the anode of the second diode is connected with the third connecting end and the connecting end of the second switch circuit, and the cathode of the second diode is connected with the first unidirectional conduction circuit.

Preferably, the energy storage circuit at least comprises an energy storage capacitor, one end of the energy storage capacitor is connected with the second follow current circuit, and the other end of the energy storage capacitor is connected with the first follow current circuit;

and/or the presence of a gas in the gas,

the first freewheeling circuit comprises at least one first inductor;

and/or the presence of a gas in the gas,

the second free-wheeling circuit comprises at least one second inductor.

Preferably, the first inductor and the second inductor constitute a coupling inductor.

the third connecting end is connected to the connecting end of the second follow current circuit and the energy storage circuit through the second switch circuit and the first switch circuit in sequence;

the third connecting end is connected to the connecting end of the first follow current circuit and the energy storage circuit through the second one-way conduction circuit and the first one-way conduction circuit in sequence;

the three-level circuit module provides the following four working modes under the control of a control signal accessed by a control end of the three-level circuit module, so that the potential at the connecting end of the second freewheeling circuit and the energy storage circuit is always higher than the potential at the connecting end of the first freewheeling circuit and the energy storage circuit, and in the whole control process, the currents flowing through the four connecting ends, namely the first connecting end, the second connecting end, the third connecting end and the fourth connecting end, are continuous:

under the working mode 1: only conducting the third end and the first end of the three-level circuit module through the first switch circuit and the second switch circuit, and disconnecting the other ends and ends of the three-level circuit module;

under the working mode 2: the third end of the three-level circuit module is unidirectionally conducted to the first end of the three-level circuit module only through the first switch circuit, the clamping circuit and the second unidirectional conducting circuit in sequence, and the other ends and the ends of the three-level circuit module are disconnected;

under the working mode 3: the second end of the three-level circuit module is connected to the first end of the three-level circuit module in a unidirectional way only through the first unidirectional conducting circuit, the clamping circuit and the second switching circuit in sequence, and the other ends of the three-level circuit module are disconnected;

working mode 4 is as follows: and only conducting the second end of the three-level circuit module to the first end of the three-level circuit module in a single direction through a first one-way conducting circuit and a second one-way conducting circuit in sequence, and disconnecting the other ends of the three-level circuit module from the first end.

Preferably, the first switch circuit at least comprises a first switch, and a first end of the first switch is connected to the connection end of the second freewheeling circuit and the energy storage circuit; the second end of the first switch is connected with the second switch circuit,

and/or the presence of a gas in the gas,

the second switch circuit at least comprises a second switch, the first end of the second switch is connected with the first switch circuit, and the second end of the second switch is connected with the third connecting end;

and/or the presence of a gas in the gas,

the clamping circuit at least comprises a clamping capacitor, one end of the clamping capacitor is connected to the connecting end of the first switch circuit and the second switch circuit, and the other end of the clamping capacitor is connected to the connecting end of the second unidirectional conducting circuit and the first unidirectional conducting circuit;

and/or the presence of a gas in the gas,

the first unidirectional conduction circuit at least comprises a first diode, and the anode of the first diode is connected with the connecting end of the energy storage circuit and the first freewheeling circuit; the cathode of the first diode is connected with the second unidirectional conducting circuit,

and/or the presence of a gas in the gas,

the second unidirectional conduction circuit at least comprises a second diode, the anode of the second diode is connected with the first unidirectional conduction circuit, and the cathode of the second diode is connected with the third connecting end.

Preferably, the energy storage circuit at least comprises an energy storage capacitor, one end of the energy storage capacitor is connected with the second follow current circuit, and the other end of the energy storage capacitor is connected with the first follow current circuit; and/or the presence of a gas in the gas,

the first freewheeling circuit comprises at least one first inductor;

and/or the presence of a gas in the gas,

the second free-wheeling circuit comprises at least one second inductor.

In a second aspect, the present invention provides a low EMI three-level dc converter, comprising a low EMI three-level dc converter unit and a dc power supply;

the positive pole of the direct-current power supply is connected with the third connecting end of the low EMI three-level direct-current converter unit, and the negative pole of the direct-current power supply is connected with the fourth connecting end of the low EMI three-level direct-current converter unit; and the first connecting end and the second connecting end of the low EMI three-level direct current converter unit are respectively used as two output ends of the low EMI three-level direct current converter unit to be connected with a load.

In a third aspect, the present invention provides a low EMI three-level dc converter, comprising a low EMI three-level dc converter unit and a dc power supply;

the positive pole of the direct current power supply is connected with the first connecting end of the low EMI three-level direct current converter unit, and the negative pole of the direct current power supply is connected with the second connecting end of the low EMI three-level direct current converter unit; and a third connecting end and a fourth connecting end of the low EMI three-level direct current converter unit are respectively used as two output ends of the low EMI three-level direct current converter unit to be connected with a load.

(III) advantageous effects

The invention provides a low EMI three-level DC converter. Compared with the prior art, the method has the following beneficial effects:

in the invention, the low EMI three-level DC converter comprises a low EMI boosting three-level DC converter and a low EMI dropping three-level DC converter. The low EMI boosting type three-level direct current converter controls the electric potentials of two end points, namely the connecting end of the second follow current circuit and the energy storage circuit and the connecting end of the first follow current circuit and the energy storage circuit through the three-level circuit module, so that the electric potential of the connecting end of the second follow current circuit and the energy storage circuit is always higher than the electric potential of the connecting end of the first follow current circuit and the energy storage circuit, and the output voltage is higher than the input voltage. The low-EMI voltage-reducing three-level direct current converter controls the electric potentials of two end points, namely the connecting end of the second follow current circuit and the energy storage circuit and the connecting end of the first follow current circuit and the energy storage circuit through the three-level circuit module, the electric potential of the connecting end of the first follow current circuit and the energy storage circuit is always lower than the electric potential of the connecting end of the second follow current circuit and the energy storage circuit, and output voltage is lower than input voltage. In the low-EMI boost-type and buck-type three-level direct current converters, the current of the input side and the current of the output side are continuous in the whole control process, so that the EMI noise of a power supply is reduced.

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 described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.

FIG. 1 is a circuit diagram of a conventional boost DC converter;

fig. 2 is a block diagram of a low EMI three-level dc converter unit according to an embodiment of the present application;

fig. 3 is a block diagram of a low EMI boost three-level dc converter according to another embodiment of the present disclosure;

FIG. 4 is a block diagram of the structure of FIG. 3 after the three-level circuit module is embodied;

fig. 5 is a circuit diagram of a low EMI boost three-level dc converter according to another embodiment of the present disclosure;

fig. 6 is a circuit diagram of an operation mode 1 corresponding to the circuit shown in fig. 5 according to another embodiment of the present application;

fig. 7 is a circuit diagram of an operation mode 2 corresponding to the circuit shown in fig. 5 according to another embodiment of the present application;

fig. 8 is a circuit diagram of an operation mode 3 corresponding to the circuit shown in fig. 5 according to another embodiment of the present application;

fig. 9 is a circuit diagram of an operation mode 4 corresponding to the circuit shown in fig. 5 according to another embodiment of the present application;

FIG. 10 is a circuit diagram of a conventional buck three-level DC converter;

fig. 11 is a block diagram of a low EMI buck three-level dc converter according to another embodiment of the present application;

FIG. 12 is a block diagram of the structure of FIG. 11 after the implementation of a three-level circuit module;

FIG. 13 is a circuit diagram of a low EMI step-down three-level DC converter according to another embodiment of the present application;

fig. 14 is a circuit diagram of an operation mode 1 corresponding to the circuit shown in fig. 13 according to another embodiment of the present application;

fig. 15 is a circuit diagram of an operation mode 2 corresponding to the circuit shown in fig. 13 according to another embodiment of the present application;

fig. 16 is a circuit diagram of an operation mode 3 corresponding to the circuit shown in fig. 13 according to another embodiment of the present application;

fig. 17 is a circuit diagram of an operation mode 4 corresponding to the circuit shown in fig. 13 according to another embodiment of the present application;

fig. 18 is a circuit diagram of a low EMI boost three-level dc converter with coupled inductors according to another embodiment of the present application;

fig. 19 is a circuit diagram of a low EMI buck three-level dc converter with coupled inductors according to another embodiment of the present application.

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 are clearly and completely described, and it is obvious that the described embodiments are a part of the embodiments of the present invention, but not all of the embodiments. 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.

It should be noted that, for convenience of description, a switching MOSFET is used as a representative controllable (on and off) switch in the present invention, but the switch in the present invention is not limited to the MOSFET. An N-channel MOSFET will be described as an example. The first terminal of the N-channel MOSFET is a drain, the second terminal is a source, and the control terminal is a gate. The control terminal of each switch in the invention applies a driving control signal. For brevity, further description is omitted. The switch in the present invention can also be implemented by using other controllable switch device besides MOSFET, such as IGBT.

Note that a diode is used to represent the one-way conduction element, but the one-way conduction element in the present invention is not limited to a diode. The anode of the diode is the anode and the cathode is the cathode. The one-way conduction element in the invention can also adopt other one-way conduction devices besides diodes. The terms "first", "second", and the like are used only for distinguishing the respective devices, and do not limit the order of the respective devices.

A conventional boost DC-DC converter topology is shown in fig. 1. When the switch S is conducted, the direct current power supply charges the L through the switch S, the inductive current is increased, the diode bears the back voltage and is forced to be cut off, and therefore the current passing through the diode is 0; when the switch S is turned off, the inductor L current continues to flow through the diode D, and the inductor L current decreases. It can be seen that the input side current of the circuit is continuous, while the output side current is discontinuous. Through the above brief analysis, it can be obtained that the currents at the input side and the output side of the conventional boost DC-DC converter cannot be guaranteed to be continuous, which causes high EMI noise, and cannot be applied to occasions with high power supply quality requirements. In addition, when the conventional boost DC-DC converter switch S is turned off, it needs to bear a higher output voltage, so that it is often difficult to select a switching device with a suitable voltage withstanding value in high-voltage and high-power applications. In view of the problems of the related art, an embodiment of the present invention provides a low EMI three-level dc converter unit, which is configured as shown in fig. 2. The low EMI three-level DC converter unit is provided with four connecting terminals including a first connecting terminal, a second connecting terminal, a third connecting terminal and a fourth connecting terminal.

The low EMI three-level DC converter unit includes: the circuit comprises a first follow current circuit, a second follow current circuit, a tank circuit and a three-level circuit module. The first connection end is connected to the second connection end sequentially through the second follow current circuit, the energy storage circuit and the first follow current circuit; the fourth connecting end is connected with the connecting end of the first follow current circuit and the second connecting end; the three-level circuit module comprises a first end, a second end and a third end, and the first end is connected with the third connecting end; the second end is connected to the connection end of the first free-wheeling circuit and the energy storage circuit (corresponding to point a in fig. 2); the third terminal is connected to the connection terminal of the tank circuit and the second freewheeling circuit (corresponding to point B in fig. 2).

The three-level circuit module is connected with a plurality of control ends and is suitable for controlling the electric potentials of two end points, namely a connecting end B of the second follow current circuit and the energy storage circuit and a connecting end A of the first follow current circuit and the energy storage circuit under the control of a control signal accessed by the control ends, so that the electric potential of the connecting end B of the second follow current circuit and the energy storage circuit is always higher than the electric potential of the connecting end A of the first follow current circuit and the energy storage circuit, and the currents flowing through the four connecting ends, namely the first connecting end, the second connecting end, the third connecting end and the fourth connecting end, are continuous in the whole control process.

Fig. 3 is a block diagram of a low EMI boost three-level dc converter according to another embodiment of the present disclosure. Referring to fig. 3, the first connection end and the second connection end are respectively connected to two ends of a load circuit, and the third connection end and the fourth connection end are respectively connected to two ends of a dc power supply. The three-level circuit module includes: the circuit comprises a first switch circuit, a second switch circuit, a clamping circuit, a first one-way conduction circuit and a second one-way conduction circuit. The positive pole of the direct current power supply is connected to the connecting end A of the first follow current circuit and the energy storage circuit through the second switch circuit and the first switch circuit in sequence; the positive electrode of the direct-current power supply is connected to the connecting end B of the energy storage circuit and the second follow current circuit through the second one-way conduction circuit and the first one-way conduction circuit in sequence; the connecting end of the second one-way conduction circuit and the first one-way conduction circuit is connected with the connecting end of the second switch circuit and the first switch circuit through a clamping circuit.

Fig. 4 is a block diagram of the three-level circuit module embodied in fig. 3, and the three-level circuit module is enclosed in a dashed line. As can be seen from the above description, the second unidirectional conducting circuit and the second switch circuit are both connected to the positive electrode of the dc power supply, that is, the second unidirectional conducting circuit is connected to the second switch circuit. The connection end of the second unidirectional conduction circuit and the second switch circuit is the first end of the three-level circuit module. One end of the first switch circuit connected to the connection end of the energy storage circuit and the first freewheeling circuit is the second end of the three-level circuit module. And one end of the first unidirectional conduction circuit connected to the connecting end of the energy storage circuit and the second freewheeling circuit is the third end of the three-level circuit module.

Fig. 5 is a circuit diagram of a low EMI boost three-level dc converter according to another embodiment of the present disclosure. The detailed description is provided below in conjunction with the specific circuit diagram provided in fig. 5.

Referring to fig. 5, the first switching circuit includes a switch S₁The second switch circuit comprises a switch S₂The first follow current circuit comprises an inductor L₁The second follow current circuit comprises an inductor L₂The energy storage circuit comprises an energy storage capacitor C, and the clamping circuit comprises a clamping capacitor C_pThe first one-way conduction circuit comprises a diode D₁And the second unidirectional conducting circuit comprises a diode D₂。

In the embodiment of the present invention, for convenience of description, a resistive load is taken as an example for analysis, that is, the load circuit includes at least one resistor R. It should be noted that, in the embodiment of the present invention, whether the load is resistive, capacitive or inductive does not affect the implementation and the effect of the embodiment of the present invention. V_inRepresenting the DC supply voltage, V_oRepresenting the output voltage, V_cRepresenting the voltage across the energy-storage capacitor C, V_cpRepresenting the voltage across the clamping capacitor. In addition, in order to improve the quality of the output waveform, an output filter capacitor C is connected in parallel between the two connecting ends of the first connecting end and the second connecting end_o。

As can be seen from fig. 5, the positive electrode of the energy storage capacitor C is connected with the inductor L₂And the negative electrode is connected with an inductor L₁. Of course, the connection relationship between the positive and negative polarities of the energy storage capacitor is not limited to this, and depends on the application of the boost three-level dc converter and the operation mode to be implemented.

Fig. 6 to 9 show four different operation modes of the low EMI boost three-level dc converter according to the embodiment of the present application. The method comprises the following specific steps:

(1) mode of operation 1. See FIG. 6, S₁And S₂On, D₁And D₂And (6) cutting off. DC power supply, S₂、S₁、L₁Forming a current loop. Wherein the input voltage V_inAll added to the inductor L₁Upper, inductor L₁The potential of point A on the connection terminal is V_in. DC power supply, S₂、S₁、C、L₂And R form another current loop. Inductor L₂Potential of point B on the connection terminal is V_in+V_c. The energy storage capacitor C is in a discharge state.

(2) Mode of operation 2. See FIG. 7, S₁Is conducted and S₂Off, D₁Cut-off, D₂And conducting. DC power supply, D₂、C_p、S₁、L₁Forming a current loop. Inductor L₁The potential of point A on the connection terminal is V_in-V_cp. DC power supply, D₂、C_p、S₁、C、L₂And R form another current loop. Inductor L₂Potential of point B on the connection terminal is V_in+V_c-V_cp. The energy storage capacitor C is in a discharging state, and the clamping capacitor C_pIn a charging state.

(3) Mode of operation 3. See FIG. 8, S₂Is conducted and S₁Off, D₁Conduction, D₂And (6) cutting off. DC power supply, S₂、C_p、D₁、C、L₁Forming a current loop. Inductor L₁The potential of point A on the connection terminal is V_in+V_cp-V_c. DC power supply, S₂、C_p、D₁、L₂And R form another current loop. Inductor L₂Potential of point B on the connection terminal is V_in+V_cp. The energy storage capacitor C is in a charging state, and the clamping capacitor C_pIs in a discharge state.

(4) And 4, working mode. See FIG. 9, S₁And S₂Off, D₁And D₂And conducting. DC power supply, D₂、D₁、C、L₁Forming a current loop. Inductor L₁The potential of point A on the connection terminal is V_in-V_c. DC power supply, D₂、D₁、L₂And R form another current loop. Inductor L₂Potential of point B on the connection terminal is V_in. The energy storage capacitor C is in a charged state.

By controlling switch S₁And S₂And when the three-level dc converter is turned on or off, the low-EMI boost-type three-level dc converter shown in fig. 5 alternately operates in a certain combination form under the above four operating modes, so as to obtain the required dc output voltage. The specific combination of the four operating modes depends on the specific modulation strategy adopted in practical application, and is not described herein.

V is preset in order to enable the three-level circuit module to output three levels_cp＝V_c/2. The potentials of the point A and the point B and the corresponding capacitances C and C in each working mode_pThe effect of (c) is shown in table 1. As can be seen from Table 1, modes 2 and 3 are redundant modes with respect to capacitance C_pThe effects of the

modes

1, 2 and 3, 4 on the capacitance C are opposite, so that the capacitance voltages can be balanced within a switching frequency by selecting a suitable redundancy mode.

TABLE 1 potentials at points A and B and Effect on capacitance

	V_A	V_B	C	C_p
					Mode of operation1	V_in	V_in+V_c	Put	-
Mode of operation 2	V_in-V_c/2	V_in+V_c/2	Put	Charging device
					Mode of operation 3	V_in-V_c/2	V_in+V_c/2	Charging device	Put
Mode of operation 4	V_in-V_c	V_in	Charging device	-

From the analysis of the above four working modes, the input current is the sum of two inductor currents, and the output current is equal to the inductor L₂The current flowing in the two inductors does not change abruptly in one switching period, so that the input current and the output current are continuous in the whole switching period, which is beneficial to reducing the EMI noise of the system.

It should be noted that the above embodiments are only some preferred modes in the present application, and in practical applications, the three-level circuit module includes a first switch circuit and a second switch circuitSwitch circuit, clamping circuit, first one-way conduction circuit and second one-way conduction circuit, switch S in first switch circuit₁A switch S in the second switching circuit₂Inductor L in the first follow current circuit₁Inductor L in the second follow current circuit₂Energy storage capacitor C in energy storage circuit and clamping capacitor C in clamping circuit_pDiode D in first unidirectional conducting circuit₁And a diode D in the second unidirectional conducting circuit₂Etc. may be replaced by other functionally identical or similar circuits. For example, the first unidirectional conduction circuit and the second unidirectional conduction circuit can be replaced by switch circuits, and the on and off of the unidirectional conduction circuits are replaced by controlling the on and off of the switch circuits.

A conventional buck three-level dc converter topology is shown in fig. 10. When the switch S₁When conducting, V_in—S₁—C_p—D₁—L—C_oAnd the R loop is conducted, and the direct current power supply supplies a capacitor C at the moment_pAnd inductor L charges, the inductor current increases. When the switch S₁At disconnection, C_p—S₂—L—(C_oAnd R) -D₂Loop is conducted, capacitor C_pThe discharge and the inductor L exchange energy and supply power to the load, and the inductor current is reduced. It can be seen that the output side current of the circuit is continuous, while the input side current is discontinuous. Through the above brief analysis, it can be obtained that the currents at the input side and the output side of the traditional step-down three-level direct current converter cannot be guaranteed to be continuous, so that high EMI noise can be caused, and the converter cannot be applied to occasions with high power supply quality requirements.

In view of the problems in the related art, another embodiment of the present application provides a low EMI step-down three-level dc converter, which is configured as shown in fig. 11. Referring to fig. 11, the low EMI buck-type three-level dc converter includes a low EMI three-level dc converter unit. The low EMI three-level DC converter unit has a first connection end, a second connection end, a third connection end and a fourth connection end. The first connecting end and the second connecting end are respectively connected with the positive pole and the negative pole of the direct-current power supply. And the third connecting end and the fourth connecting end are respectively connected with two ends of the load circuit.

The low EMI three-level DC converter unit includes: the circuit comprises a first follow current circuit, a second follow current circuit, a tank circuit and a three-level circuit module. The first connection end is connected to the second connection end sequentially through the second follow current circuit, the energy storage circuit and the first follow current circuit; the fourth connecting end is connected with the connecting end of the first follow current circuit and the second connecting end; the three-level circuit module comprises a first end, a second end and a third end, and the first end is connected with the third connecting end; the second end is connected to the connection end of the first free-wheeling circuit and the energy storage circuit (corresponding to point a in fig. 11); the third terminal is connected to the connection terminal of the tank circuit and the second freewheeling circuit (corresponding to point B in fig. 11).

Fig. 12 is a block diagram of the three-level circuit module embodied in fig. 11, and the three-level circuit module is enclosed by a dotted line. Referring to fig. 12, the first connection end and the second connection end are respectively connected to two ends of the dc power source, and the third connection end and the fourth connection end are respectively connected to two ends of the load circuit. The three-level circuit module includes: the third connecting end is connected to the connecting end B of the second follow current circuit and the energy storage circuit through the second switch circuit and the first switch circuit in sequence; the third connecting end is connected to the connecting end A of the first follow current circuit and the energy storage circuit through the second one-way conduction circuit and the first one-way conduction circuit in sequence; the connecting end of the second one-way conduction circuit and the first one-way conduction circuit is connected with the connecting end of the second switch circuit and the first switch circuit through a clamping circuit.

As can be seen from the above description, the second unidirectional conducting circuit and the second switch circuit are both connected to the third connection terminal, that is, the second unidirectional conducting circuit is connected to the second switch circuit. The connection end of the second unidirectional conduction circuit and the second switch circuit is the first end of the three-level circuit module. And one end of the first unidirectional conduction circuit connected to the connecting end of the energy storage circuit and the first follow current circuit is the second end of the three-level circuit module. And one end of the first switch circuit connected to the connecting end of the energy storage circuit and the second freewheeling circuit is the third end of the three-level circuit module.

Fig. 13 is a circuit diagram of a low EMI buck three-level dc converter according to another embodiment of the present application. The detailed description is provided below in conjunction with the specific circuit diagram provided in fig. 13.

Referring to fig. 13, the first switching circuit includes a switch S₁The second switch circuit comprises a switch S₂The first follow current circuit comprises an inductor L₁The second follow current circuit comprises an inductor L₂The energy storage circuit comprises an energy storage capacitor C, and the clamping circuit comprises a clamping capacitor C_pThe first one-way conduction circuit comprises a diode D₁And the second unidirectional conducting circuit comprises a diode D₂。

In the embodiment of the present invention, for convenience of description, a resistive load is taken as an example for analysis, that is, the load circuit includes at least one resistor R. It should be noted that, in the embodiment of the present invention, whether the load is resistive, capacitive or inductive does not affect the implementation and the effect of the embodiment of the present invention. V_inRepresenting the DC supply voltage, V_oRepresenting the output voltage, V_cRepresenting the voltage across the energy-storage capacitor C, V_cpRepresenting the voltage across the clamping capacitor. In addition, in order to improve the quality of the output waveform, the third connection terminal and the fourth connection terminal are connectedAn output filter capacitor C is connected in parallel_o。

As can be seen from fig. 13, the positive electrode of the energy storage capacitor C is connected to the inductor L₂And the negative electrode is connected with an inductor L₁. Of course, the connection relationship between the positive and negative polarities of the energy storage capacitor is not limited to this, and depends on the application of the low EMI step-down three-level dc converter and the operation mode to be implemented.

Fig. 14 to 17 illustrate four different operation modes of the low EMI step-down three-level dc converter according to the embodiment of the present application. The method comprises the following specific steps:

(1) mode of operation 1. See FIG. 14, S₁And S₂On, D₁And D₂And (6) cutting off. R, S₂、S₁、C、L₁Forming a current loop. Wherein, the additional inductance L₁The potential of point A on the connection terminal is V_o-V_c。R、S₂、S₁、L₂And the direct current power supply forms another current loop. Inductor L₂Potential of point B on the connection terminal is V_o. The energy storage capacitor C is in a discharge state.

(2) Mode of operation 2. See FIG. 15, S₁Is conducted and S₂Off, D₁Cut-off, D₂And conducting. R, D₂、C_p、S₁、C、L₁Forming a current loop. Inductor L₁The potential of point A on the connection terminal is V_o+V_cp-V_c。R、D₂、C_p、S₁、L₂And the direct current power supply forms another current loop. Inductor L₂Potential of point B on the connection terminal is V_o+V_cp. The energy storage capacitor C is in a discharging state, and the clamping capacitor C_pIn a charging state.

(3) Mode of operation 3. See FIG. 16, S₂Is conducted and S₁Off, D₁Conduction, D₂Cut-off, R, S₂、C_p、D₁、L₁Forming a current loop. Inductor L₁The potential of point A on the connection terminal is V_o-V_cp。R、S₂、C_p、D₁、C、L₂And the direct current power supply forms another current loop. Inductor L₂Potential V of upper point B_o-V_cp+V_c. The energy storage capacitor C is in a charging state, and the clamping capacitor C_pIs in a discharge state.

(4) And 4, working mode. See FIG. 17, S₁And S₂Off, D₁And D₂And conducting. R, D₂、D₁、L₁Forming a current loop. Inductor L₁The potential of point A on the connection terminal is V_o。R、D₂、D₁、C、L₂And the direct current power supply forms another current loop. Inductor L₂Potential of point B on the connection terminal is V_o+V_c. The energy storage capacitor C is in a charged state.

By controlling switch S₁And S₂And when the low-EMI step-down three-level dc converter shown in fig. 13 is turned on or off, the converter alternately operates in a certain combination mode in the above four operation modes, so as to obtain a required dc output voltage. The specific combination of the four operating modes depends on the specific modulation strategy adopted in practical application, and is not described herein.

V is preset in order to enable the three-level circuit module to output three levels_cp＝V_c/2. The potentials of the point A and the point B and the corresponding capacitances C and C in each working mode_pThe effect of (c) is shown in table 2. As can be seen from Table 2, modes 2 and 3 are redundant modes with respect to capacitance C_pThe effects of the

modes

TABLE 2 potentials at points A and B and Effect on capacitance

	V_A	V_B	C	C_p
					Mode of operation 1	V_o-V_c	V_o	Put	-
Mode of operation 2	V_o-V_c/2	V_o+V_c/2	Put	Charging device
					Mode of operation 3	V_o-V_c/2	V_o+V_c/2	Charging device	Put
Mode of operation 4	V_o	V_o+V_c	Charging device	-

From top to bottomThe analysis of the four working modes shows that the output current is the sum of two inductive currents, and the input current is equal to the inductance L₂The current flowing in the two inductors does not change abruptly in one switching period, so that the input current and the output current are continuous in the whole switching period, which is beneficial to reducing the EMI noise of the system.

It should be noted that the foregoing embodiments are only some preferred modes in this application, and in practical applications, the three-level circuit module includes a first switch circuit, a second switch circuit, a clamping circuit, a first unidirectional conducting circuit and a second unidirectional conducting circuit, where a switch S in the first switch circuit is connected to the first unidirectional conducting circuit and the second unidirectional conducting circuit₁A switch S in the second switching circuit₂Inductor L in the first follow current circuit₁Inductor L in the second follow current circuit₂Energy storage capacitor C in energy storage circuit and clamping capacitor C in clamping circuit_pDiode D in first unidirectional conducting circuit₁And a diode D in the second unidirectional conducting circuit₂Etc. may be replaced by other functionally identical or similar circuits. If the first one-way conduction circuit and the second one-way conduction circuit can be replaced by switch circuits, the switch circuits are controlled to be switched off and switched on to replace the switch circuits to be switched off and switched on.

The coupled inductor technology can theoretically realize zero ripple of output current, and the technology is applied to various basic DC/DC converters, so that the output current ripple of the converter can be greatly reduced, and the working characteristics of the converter are better. The low EMI three-level DC converter provided by the embodiment of the application can replace the inductor in the DC converter with the coupling inductor by applying the coupling inductor technology, so that the output current ripple can be reduced. Inductor L in FIG. 5 as in the previous embodiment₁And an inductance L₂May be replaced with a coupled inductor as in fig. 18. Inductor L as in FIG. 13 in example 2₁And an inductance L₂May be replaced with a coupled inductor as in fig. 19.

Referring to fig. 18, the inductance L₁And L₂The relationship between the voltage across the two terminals and the flowing current can be expressed as:

from formula (9):

in the formula L_e1、L_e2Are respectively an inductance L₁And L₂The equivalent inductance in a transformer with coupled inductance, M represents the mutual inductance. The coupling coefficient K and the coil turns ratio n can be expressed as:

then L is₁And L₂Equivalent inductance L of_e1、L_e2Can be respectively represented as

The equivalent inductance is infinite, the current ripple is infinitesimal, in order to make the equivalent inductance L_e2Infinity, if n is K in formula (12), then

The inductive current ripple i can be obtained by bringing the formula (13) into the formula (10)_L2Approximately 0, i.e., the output current ripple is approximately 0.

In summary, compared with the prior art, the embodiment of the present application has the following beneficial effects:

1. the embodiment of the invention provides the three-level direct current converter with continuous input current and output current, and the EMI noise of a power supply is reduced.

2. The embodiment of the invention realizes low ripple of output current by the coupling inductance technology without adding additional auxiliary and control circuits, and the method is simple and easy to implement.

It is noted that, herein, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, 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.

The above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.

Claims

1. A low EMI three-level dc converter unit having four connection terminals in total, a first connection terminal, a second connection terminal, a third connection terminal and a fourth connection terminal, comprising: the circuit comprises a first follow current circuit, a second follow current circuit, an energy storage circuit and a three-level circuit module; wherein the content of the first and second substances,

2. The low EMI three-level dc converter unit of claim 1, wherein the three-level circuit module comprises: a first switch circuit, a second switch circuit, a clamping circuit, a first one-way conduction circuit and a second one-way conduction circuit,

the four working modes include:

3. The low EMI three-level DC converter unit of claim 2,

the first switch circuit at least comprises a first switch, the first end of the first switch is connected with the second switch circuit, and the second end of the first switch is connected with the connection end of the first freewheeling circuit and the energy storage circuit;

and/or the presence of a gas in the gas,

4. The low EMI three-level dc converter unit of claim 1 wherein the energy storage circuit includes at least one energy storage capacitor, one end of the energy storage capacitor being connected to the second freewheeling circuit and the other end of the energy storage capacitor being connected to the first freewheeling circuit;

and/or the presence of a gas in the gas,

the first freewheeling circuit comprises at least one first inductor;

and/or the presence of a gas in the gas,

the second free-wheeling circuit comprises at least one second inductor.

5. The low EMI three-level dc converter unit of claim 4 wherein the first inductor and the second inductor form a coupled inductor.

6. The low EMI three-level dc converter unit of claim 1, wherein the three-level circuit module comprises: a first switch circuit, a second switch circuit, a clamping circuit, a first one-way conduction circuit and a second one-way conduction circuit,

7. The low EMI three-level DC converter unit of claim 6,

the first switch circuit at least comprises a first switch, and the first end of the first switch is connected with the connecting end of the second freewheeling circuit and the energy storage circuit; the second end of the first switch is connected with the second switch circuit,

and/or the presence of a gas in the gas,

8. The low EMI three-level dc converter unit of claim 6 wherein the energy storage circuit includes at least one energy storage capacitor, one end of the energy storage capacitor being connected to the second freewheeling circuit and the other end of the energy storage capacitor being connected to the first freewheeling circuit; and/or the presence of a gas in the gas,

the first freewheeling circuit comprises at least one first inductor;

and/or the presence of a gas in the gas,

the second free-wheeling circuit comprises at least one second inductor.

9. The low EMI three-level dc converter unit of claim 8 wherein the first inductor and the second inductor form a coupled inductor.

10. A low EMI three-level DC converter comprising a low EMI three-level DC converter unit as claimed in any one of claims 1 to 5 and a DC power supply;

11. A low EMI three-level dc-to-dc converter comprising a low EMI three-level dc-to-dc converter unit as claimed in any one of claims 1, 6 to 9 and a dc power supply;