A three-port bidirectional DC / DC converter soft switching circuit and device

Abstract

The present invention provides a three-port bidirectional DC / DC converter soft-switching circuit and device thereof, comprising a first bridge arm, a second bridge arm, a filter circuit, a winding transformer, and a third-port circuit. The first bridge arm is connected in parallel with a high-voltage DC bus, the second bridge arm is located on either side of the first bridge arm, the center of the first bridge arm is electrically connected to the center of the second bridge arm via the first winding loop of the winding transformer, the second bridge arm is electrically connected to a battery via the filter circuit, and the third-port circuit is electrically connected to the first winding loop of the winding transformer via the second winding of the winding transformer. The control ends of the first and second bridge arms are electrically connected to the output ends of a controller, and the third-port circuit is configured to obtain resonant energy through the second winding of the winding transformer and provide the resonant energy to a DC load. This circuit is designed to achieve soft switching operation in a non-isolated multi-port converter during bidirectional conversion, thereby improving system efficiency and power density.

Description

Technical Field

[0001] The present invention relates to the technical field of soft switching, and in particular to a three-port bidirectional DC / DC converter soft switching circuit and a device thereof. Background Art

[0002] At present, the research on multi-port converters is mainly based on dual active bridge circuits, and the multi-port converters in the existing technology mostly adopt isolated multi-port bidirectional converter solutions and three-port bidirectional DC / DC converter solutions for DC microgrids. Among them, the isolated multi-port bidirectional converter constructs a three-port DC / DC converter through a dual active bridge, and although it can fully utilize the soft switching principle of the full-bridge circuit to achieve overall soft switching operation, its structure is complex and there are transformer and rectifier losses, which makes it unsuitable for non-isolated applications. The three-port bidirectional DC / DC converter for DC microgrids is a non-isolated multi-port DC / DC converter. During use, the soft switching problem of the switching devices in the system is not considered, and the switching loss limits the overall conversion efficiency and power density.

[0003] In view of this, this application is filed. Summary of the Invention

[0004] The purpose of the present invention is to provide a three-port bidirectional DC / DC converter soft switching circuit and device thereof, aiming to realize soft switching operation of a non-isolated multi-port converter during bidirectional conversion, thereby improving system efficiency and power density.

[0005] The present invention discloses a three-port bidirectional DC / DC converter soft switching circuit, comprising a first bridge arm, a second bridge arm, a filter circuit, a winding transformer and a third port circuit;

[0006] The first bridge arm is connected in parallel with the high-voltage DC bus, the second bridge arm is on both sides of the first bridge arm, the center of the first bridge arm is electrically connected to the center of the second bridge arm through the first winding loop of the winding transformer, the second bridge arm is electrically connected to the battery through the filter circuit, and the third port circuit is electrically connected to the first winding loop of the winding transformer through the second winding of the winding transformer;

[0007] The control ends of the first bridge arm and the second bridge arm are used to be electrically connected to the output end of the controller, and the third port circuit is configured to obtain resonant energy through the second winding of the winding transformer and provide the resonant energy to the DC load.

[0008] Preferably, the first bridge arm includes a first auxiliary bridge arm switch and a second auxiliary bridge arm switch, the drain of the first auxiliary bridge arm switch is used to be electrically connected to the positive pole of the high-voltage DC bus, the source of the first auxiliary bridge arm switch is electrically connected to the first end of the first winding loop of the winding transformer, the drain of the second auxiliary bridge arm switch is electrically connected to the first end of the first winding loop of the winding transformer, and the source of the second auxiliary bridge arm switch is used to be electrically connected to the negative pole of the high-voltage DC bus.

[0009] Preferably, the second bridge arm includes a first main bridge arm switch and a second main bridge arm switch, the drain of the first main bridge arm switch is used to be electrically connected to the positive pole of the high-voltage DC bus, the source of the first main bridge arm switch is electrically connected to the second end of the first winding loop of the winding transformer, the drain of the second main bridge arm switch is electrically connected to the second end of the first winding loop of the winding transformer, and the source of the second main bridge arm switch is used to be electrically connected to the negative pole of the high-voltage DC bus.

[0010] Preferably, the filter circuit includes a resonant capacitor and a filter inductor, one end of the resonant capacitor is used to be electrically connected to the negative pole of the battery, the other end of the resonant capacitor is electrically connected to one end of the filter inductor, and the other end of the filter inductor is used to be electrically connected to the positive pole of the battery.

[0011] Preferably, the third port circuit includes a diode uncontrolled rectifier bridge and a filter capacitor, the negative pole of the diode uncontrolled rectifier bridge is electrically connected to the same-name end of the second winding of the winding transformer, the positive pole of the diode uncontrolled rectifier bridge is electrically connected to the opposite-name end of the second winding of the winding transformer, the positive pole of the filter capacitor is electrically connected to the negative pole of the diode uncontrolled rectifier bridge, the negative pole of the filter capacitor is electrically connected to the positive pole of the diode uncontrolled rectifier bridge, and the filter capacitor is used to be connected in parallel with a DC load.

[0012] Preferably, the first winding loop includes a resonant inductor and a first winding transformer, one end of the resonant inductor is electrically connected to the source of the first auxiliary bridge arm switch, the other end of the resonant inductor is electrically connected to the same-name end of the first winding transformer, and the opposite-name end of the first winding transformer is electrically connected to the source of the first main bridge arm switch.

[0013] Preferably, the first auxiliary bridge arm switch, the second auxiliary bridge arm switch, the first main bridge arm switch and the second main bridge arm switch are NMOS tubes.

[0014] The present invention also provides a three-port bidirectional DC / DC converter soft switching device, comprising a controller, a high-voltage DC bus, a battery, a DC load, and the three-port bidirectional DC / DC converter soft switching circuit described in any one of the above items, wherein the output end of the controller is electrically connected to the control ends of the first bridge arm and the second bridge arm, the high-voltage DC bus is connected in parallel with the first bridge arm, the second bridge arm is electrically connected to the battery via the filter circuit, and the DC load is connected in parallel with the filter capacitor.

[0015] In summary, this embodiment provides a three-port bidirectional DC / DC converter soft switching circuit and device thereof. When the battery needs to be charged, power flows from the high-voltage DC bus to the battery, and the circuit enters the buck mode. After the resonant energy passes through the winding transformer and the third port circuit, a DC voltage is output to provide energy for the DC load. The resonant energy is directly transferred to the load through primary power. When the battery needs to be discharged, power flows from the storage current to the high-voltage DC bus, and the circuit enters the boost mode. Its operating principle is the same as that of the above-mentioned buck mode, thereby realizing soft switching operation of the non-isolated multi-port converter during the bidirectional conversion process, thereby improving system efficiency and power density. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The invention is a circuit diagram of an isolated multi-port bidirectional converter in the prior art.

[0017] Figure 2 This is a circuit diagram of a three-port bidirectional DC / DC converter for a DC microgrid in the prior art.

[0018] Figure 3 The present invention provides a three-port bidirectional DC / DC converter soft switching circuit and a circuit diagram of the device thereof.

[0019] Figure 4 This is a schematic diagram of an equivalent circuit of a three-port bidirectional DC / DC converter soft switching circuit and its device in buck mode provided by an embodiment of the present invention.

[0020] Figure 5 This is a schematic diagram of the principle waveforms of the buck mode of a three-port bidirectional DC / DC converter soft switching circuit and its device provided by an embodiment of the present invention.

[0021] Figure 6 This is a schematic diagram of the equivalent circuits of the three-port bidirectional DC / DC converter soft switching circuit and its device at each stage of the buck mode provided by an embodiment of the present invention.

[0022] Figure 7 The diagram is a circuit diagram of a three-port bidirectional DC / DC converter soft switching circuit and a boost mode device thereof provided by an embodiment of the present invention.

[0023] Figure 8 The present invention provides a three-port bidirectional DC / DC converter soft switching circuit and a power flow and decoupling control schematic diagram of the device. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the invention for which protection is sought, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0025] The specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0026] See also Figure 3 , a first embodiment of the present invention provides a three-port bidirectional DC / DC converter soft switching circuit, comprising a first bridge arm, a second bridge arm, a filter circuit, a winding transformer T, and a third port circuit Ua;

[0027] The first bridge arm is connected in parallel with the high-voltage DC bus Ubus, the second bridge arm is on both sides of the first bridge arm, the center of the first bridge arm is electrically connected to the center of the second bridge arm through the first winding loop of the winding transformer T, the second bridge arm is electrically connected to the battery Ubat through the filter circuit, and the third port circuit is electrically connected to the first winding loop of the winding transformer T through the second winding N2 of the winding transformer T;

[0028] The control ends of the first bridge arm and the second bridge arm are used to be electrically connected to the output end of the controller, and the third port circuit is configured to obtain resonant energy through the second winding N2 of the winding transformer T and provide the resonant energy to the DC load.

[0029] It should be noted that the inventors have found that the isolated multi-port bidirectional converter in the prior art, such as Figure 1As shown in FIG, a three-port DC / DC converter is constructed by dual active bridges, which can fully utilize the soft-opening principle of the full-bridge circuit to achieve overall soft switching operation. However, the structure is complex, and there are transformer and rectifier losses, which makes it unsuitable for non-isolated applications. The three-port bidirectional DC / DC converter for DC microgrids in the prior art, such as Figure 2 As shown, half-bridge switches SS1 and SS2 simultaneously serve as the energy exchange interface between the DC bus, the energy storage battery Vbat, and the photovoltaic panel Vpv. The photovoltaic cell Vpv outputs power in one direction, while power can flow bidirectionally between the DC bus and the energy storage battery. In this solution, SS1 and SS2 operate in a hard-switching state.

[0030] Specifically, in this embodiment, the high-voltage DC bus Ubus and the battery Ubat are two voltage sources respectively, which output to each other, and the voltage value of the high-voltage DC bus Ubus is greater than the voltage value of the battery Ubat. When the battery Ubat needs to be charged, power flows from the high-voltage DC bus Ubus to the battery Ubat, and the three-port bidirectional DC / DC converter soft switching circuit enters the buck mode; when the battery Ubat needs to be discharged, power flows from the battery Ubat to the high-voltage DC bus Ubus, and the three-port bidirectional DC / DC converter soft switching circuit enters the boost mode.

[0031] See also Figure 4 In this embodiment, the first bridge arm includes a first auxiliary bridge arm switch Sa1 and a second auxiliary bridge arm switch Sa2. The drain of the first auxiliary bridge arm switch Sa1 is electrically connected to the positive electrode of the high-voltage DC bus Ubus, the source of the first auxiliary bridge arm switch Sa1 is electrically connected to the first end of the first winding loop of the winding transformer T, the drain of the second auxiliary bridge arm switch Sa2 is electrically connected to the first end of the first winding loop of the winding transformer T, and the source of the second auxiliary bridge arm switch Sa2 is electrically connected to the negative electrode of the high-voltage DC bus Ubus. The second bridge arm includes a first main bridge arm switch S1 and a second main bridge arm switch S2. The drain of the first main bridge arm switch S1 is electrically connected to the positive electrode of the high-voltage DC bus Ubus, the source of the first main bridge arm switch S1 is electrically connected to the second end of the first winding loop of the winding transformer T, the drain of the second main bridge arm switch S2 is electrically connected to the second end of the first winding loop of the winding transformer T, and the source of the second main bridge arm switch S2 is electrically connected to the negative electrode of the high-voltage DC bus Ubus.

[0032] The first auxiliary bridge arm switch Sa1, the second auxiliary bridge arm switch Sa2, the first main bridge arm switch S1, and the second main bridge arm switch S2 are NMOS transistors. It should be noted that in other embodiments, other types of bridge arm switches may also be used, which are not specifically limited here, but all such solutions are within the scope of protection of the present invention.

[0033] In buck mode, the first main bridge arm switch S1 is the main control switch, and its working duty cycle is defined as the duty cycle of the system. The parasitic diode of the second main bridge arm switch S2 serves as the freewheeling diode Ds2, the first auxiliary bridge arm switch Sa1 is the control switch, and the second auxiliary bridge arm switch Sa2 remains in a blocked state. In order to achieve soft switching operation of the first main bridge arm switch S1 and the second main bridge arm switch S2, the first auxiliary bridge arm switch Sa1 is turned on for a period of time before the first main bridge arm switch S1 is turned on; in buck mode, the resonant energy outputs a DC voltage after passing through the winding transformer and the diode uncontrolled rectifier bridge BD1 and the filter capacitor Ca to provide energy for the DC load, and the resonant energy is directly transferred to the load through primary power.

[0034] Specifically, in this embodiment, the filter circuit includes a resonant capacitor Cr and a filter inductor Ca, one end of the resonant capacitor Cr is electrically connected to the negative electrode of the battery Ubat, the other end of the resonant capacitor Cr is electrically connected to one end of the filter inductor Lf, and the other end of the filter inductor Lf is electrically connected to the positive electrode of the battery Ubat. The third port circuit includes a diode uncontrolled rectifier bridge BD1 and a filter capacitor Ca, the negative electrode of the diode uncontrolled rectifier bridge BD1 is electrically connected to the same-name end of the second winding N2 of the winding transformer T, the positive electrode of the diode uncontrolled rectifier bridge BD1 is electrically connected to the opposite-name end of the second winding N2 of the winding transformer T, the positive electrode of the filter capacitor Ca is electrically connected to the negative electrode of the diode uncontrolled rectifier bridge BD1, and the negative electrode of the filter capacitor Ca is electrically connected to the positive electrode of the diode uncontrolled rectifier bridge BD1, and the filter capacitor Ca is used to be connected in parallel with a DC load. In which, the first winding loop includes a resonant inductor Lr and a first winding transformer N1, one end of the resonant inductor Lr is electrically connected to the source of the first auxiliary bridge arm switch Sa1, the other end of the resonant inductor Lr is electrically connected to the same-name end of the first winding transformer N1, and the opposite-name end of the first winding transformer N1 is electrically connected to the source of the first main bridge arm switch S1.

[0035] See also Figures 5 and 6In this embodiment, to facilitate the analysis of the soft switching working principle, it is assumed that the filter inductor Lf and the filter capacitor Ca are large enough, and their ripple components are ignored. The current of the filter inductor Lf can be approximately constant, and the port voltage is constant. Before time t0, the equivalent circuit is as follows: Figure 6 As shown in (a), the current of the filter inductor Lf is continuously flowing through the freewheeling diode Ds2 of the second main bridge arm switch S2, and the working state is the same as that of the hard switch buck.

[0036] Phase 1 [t0, t1], the equivalent circuit is as follows Figure 6 As shown in (b), at time t0, the first auxiliary bridge arm switch Sa1 is turned on in advance of the first main bridge arm switch S1, and the current of the resonant inductor Lr rises linearly from 0. However, since the current of the resonant inductor Lr is less than the current of the filter inductor Lf, the freewheeling diode Ds2 of the second main bridge arm switch S2 is still turned on; while the resonant inductor Lr stores energy, the input power supply directly supplies power to the load through the winding transformer T and the diode uncontrolled rectifier bridge BD1.

[0037] Phase 2[t1,t2]: Equivalent circuit is as follows Figure 6 As shown in (c), at time t1, the current of the resonant inductor Lr is equal to the current of the filter inductor Lf, the current of the freewheeling diode Ds2 of the second main bridge arm switch S2 is zero, the freewheeling diode Ds2 of the second main bridge arm switch S2 is soft-turned off, and the resonant inductor Lr and the resonant capacitor Cr start a resonance process. At this time, the resonant frequency is greater than the switching frequency, the voltage of the resonant capacitor Cr gradually increases, and the corresponding voltage of the first main bridge arm switch S1 gradually decreases.

[0038] Phase 3[t2,t3]: Equivalent circuit is as follows Figure 6 As shown in (d), at time t2, the voltage of the first main bridge arm switch S1 drops to zero, and the parasitic diode of the first main bridge arm switch S1 is turned on, creating conditions for the first main bridge arm switch S1 to achieve zero voltage turn-on; the current of the resonant inductor Lr begins to decrease linearly until the current of the resonant inductor Lr is equal to the current of the filter inductor Lf. At this time, as long as an opening signal is given to the first main bridge arm switch S1 at this stage, the first main bridge arm switch S1 can achieve zero voltage turn-on.

[0039] Phase 4[t3,t4]: Equivalent circuit is as follows Figure 6As shown in (e), after time t3, the current of the resonant inductor Lr is less than the current of the filter inductor Lf. At this time, the first main bridge arm switch S1 flows through the forward current, and the current of the resonant inductor Lr continues to decrease until the current of the resonant inductor Lr is reduced to zero. Thereafter, the first auxiliary bridge arm switch Sa1 is disconnected to achieve zero-current shutdown of the first auxiliary bridge arm switch Sa1 and the diode uncontrolled rectifier bridge BD1. If the actual reverse recovery characteristics of the diode of the diode uncontrolled rectifier bridge BD1 are considered, a short oscillation process will occur.

[0040] Phase 5[t4,t5]: Equivalent circuit is as follows Figure 6 As shown in (f), after time t4, the auxiliary network current is zero, the current of the winding transformer T is also zero, and the current enters the normal conduction process of the first main bridge arm switch S1. At this time, the current of the first main bridge arm switch S1 is equal to the current of the filter inductor Lf.

[0041] Phase 6[t5,t6]: Equivalent circuit is as follows Figure 6 As shown in (g), at time t5, the first main bridge arm switch S1 is turned off. Due to the resonance of the resonant capacitor Cr, the voltage of the first main bridge arm switch S1 rises linearly, and the corresponding voltage of the freewheeling diode Ds2 of the second main bridge arm switch S2 decreases linearly, and the first main bridge arm switch S1 achieves zero voltage shutdown. Until time t6, the voltage of the resonant capacitor Cr drops to zero, and the freewheeling diode Ds2 of the second main bridge arm switch S2 turns on, providing a freewheeling path for the filter inductor Lf, returning to the freewheeling state before t0 and waiting for the arrival of the next switching cycle.

[0042] See also Figure 7 In this embodiment, in boost mode, the second main arm switch S2 serves as the main control switch, and the operating duty cycle of the second main arm switch S2 is defined as the duty cycle of the system. The parasitic diode of the first main arm switch S1 serves as a freewheeling diode Ds1, and the second auxiliary arm switch Sa2 serves as a control switch. The first auxiliary arm switch Sa1 remains in a blocked state. To achieve soft switching operation of the first main arm switch S1 and the second main arm switch S2, the second auxiliary arm switch Sa2 is turned on for a period of time before the second main arm switch S2 is turned on. In boost mode, the resonant energy outputs a DC voltage after passing through the winding transformer T, the diode uncontrolled rectifier bridge BD1, and the filter capacitor Ca, providing energy for the DC load. The resonant energy is directly transferred to the load through primary power. The soft switching principle of the boost mode is the same as the soft switching principle of the aforementioned buck mode.

[0043] Through the analysis of the operating states of the buck mode and boost mode equivalent circuits at each stage, it can be seen that the soft-switching circuit of the three-port bidirectional DC / DC converter can directly transmit the resonant energy to the third port through the winding transformer T to power the DC load, rather than exchanging it between the auxiliary network and the power supply side to form a reactive circulating current. At the same time, soft-switching operation of all switching devices in the original power circuit and the auxiliary resonant network is achieved. Among them, the voltage and current stresses of each switch tube and diode in the three-port bidirectional DC / DC converter soft-switching circuit and the second bridge arm are not increased due to the addition of the resonant circuit, and the converter has higher power conversion efficiency.

[0044] See also Figure 8 Through the aforementioned analysis of the operating principle, it can be seen that the power control between the high-voltage DC bus Ubus and the battery Ubat is achieved by the duty cycle of the first main bridge arm switch S1 and the second main bridge arm switch S2. Each time the main bridge arm switches, it outputs a certain amount of energy to the third port circuit, and the amount of energy output per time is related to factors such as the power transmission between the high-voltage DC bus Ubus and the battery Ubat. Therefore, to decouple the control of the third port, the output power of the third port can be controlled by adjusting the operating frequency of the main bridge arm switch, thereby achieving power decoupling control between the three ports.

[0045] A second embodiment of the present invention provides a three-port bidirectional DC / DC converter soft switching device, including a controller, a high-voltage DC bus Ubus, a battery Ubat, a DC load Rdc, and a three-port bidirectional DC / DC converter soft switching circuit as described in any one of the above items, wherein the output end of the controller is electrically connected to the control end of the first bridge arm and the second bridge arm, the high-voltage DC bus Ubus is connected in parallel with the first bridge arm, the second bridge arm is electrically connected to the battery Ubat through the filter circuit, and the DC load Rdc is connected in parallel with the filter capacitor.

[0046] The above are only preferred embodiments of the present invention. The protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention.

Claims

1. A three-port bidirectional DC / DC converter soft switching circuit, characterized in that: It includes a first bridge arm, a second bridge arm, a filter circuit, a winding transformer and a third port circuit; The first bridge arm is connected in parallel with the high-voltage DC bus, the second bridge arm is on both sides of the first bridge arm, the center of the first bridge arm is electrically connected to the center of the second bridge arm through the first winding loop of the winding transformer, the second bridge arm is electrically connected to the battery through the filter circuit, and the third port circuit is electrically connected to the first winding loop of the winding transformer through the second winding of the winding transformer; The control ends of the first bridge arm and the second bridge arm are used to be electrically connected to the output end of the controller, and the third port circuit is configured to obtain resonant energy through the second winding of the winding transformer and provide the resonant energy to the DC load.

2. A three-port bidirectional DC / DC converter soft switching circuit according to claim 1, characterized in that: The first bridge arm includes a first auxiliary bridge arm switch and a second auxiliary bridge arm switch, the drain of the first auxiliary bridge arm switch is used to be electrically connected to the positive pole of the high-voltage DC bus, the source of the first auxiliary bridge arm switch is electrically connected to the first end of the first winding loop of the winding transformer, the drain of the second auxiliary bridge arm switch is electrically connected to the first end of the first winding loop of the winding transformer, and the source of the second auxiliary bridge arm switch is used to be electrically connected to the negative pole of the high-voltage DC bus.

3. A three-port bidirectional DC / DC converter soft switching circuit according to claim 2, characterized in that: The second bridge arm includes a first main bridge arm switch and a second main bridge arm switch, the drain of the first main bridge arm switch is used to be electrically connected to the positive pole of the high-voltage DC bus, the source of the first main bridge arm switch is electrically connected to the second end of the first winding loop of the winding transformer, the drain of the second main bridge arm switch is electrically connected to the second end of the first winding loop of the winding transformer, and the source of the second main bridge arm switch is used to be electrically connected to the negative pole of the high-voltage DC bus.

4. The three-port bidirectional DC / DC converter soft switching circuit according to claim 1, characterized in that: The filter circuit includes a resonant capacitor and a filter inductor, one end of the resonant capacitor is used to be electrically connected to the negative pole of the battery, the other end of the resonant capacitor is electrically connected to one end of the filter inductor, and the other end of the filter inductor is used to be electrically connected to the positive pole of the battery.

5. The three-port bidirectional DC / DC converter soft switching circuit according to claim 1, characterized in that: The third port circuit includes a diode uncontrolled rectifier bridge and a filter capacitor. The negative pole of the diode uncontrolled rectifier bridge is electrically connected to the same-name end of the second winding of the winding transformer, the positive pole of the diode uncontrolled rectifier bridge is electrically connected to the opposite-name end of the second winding of the winding transformer, the positive pole of the filter capacitor is electrically connected to the negative pole of the diode uncontrolled rectifier bridge, and the negative pole of the filter capacitor is electrically connected to the positive pole of the diode uncontrolled rectifier bridge. The filter capacitor is used to be connected in parallel with a DC load.

6. The three-port bidirectional DC / DC converter soft switching circuit according to claim 3, characterized in that: The first winding loop includes a resonant inductor and a first winding transformer, one end of the resonant inductor is electrically connected to the source of the first auxiliary bridge arm switch, the other end of the resonant inductor is electrically connected to the same-name end of the first winding transformer, and the opposite-name end of the first winding transformer is electrically connected to the source of the first main bridge arm switch.

7. The three-port bidirectional DC / DC converter soft switching circuit according to claim 3, characterized in that: The first auxiliary bridge arm switch, the second auxiliary bridge arm switch, the first main bridge arm switch and the second main bridge arm switch are NMOS tubes.

8. A three-port bidirectional DC / DC converter soft switching device, characterized in that: The three-port bidirectional DC / DC converter soft-switching circuit comprises a controller, a high-voltage DC bus, a battery, a DC load, and the soft-switching circuit of any one of claims 1 to 7, wherein the output end of the controller is electrically connected to the control ends of the first bridge arm and the second bridge arm, the high-voltage DC bus is connected in parallel with the first bridge arm, the second bridge arm is electrically connected to the battery through the filter circuit, and the DC load is connected in parallel with the filter capacitor.

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