Soft-switching circuit and device of a half-bridge bidirectional DC / DC converter

Abstract

The present invention provides a soft-switching circuit and device for a half-bridge bidirectional DC / DC converter, including a first voltage source, a first bridge arm, a second bridge arm, a filtering circuit, a second voltage source, and a three-winding transformer; the first bridge arm is connected in parallel on both sides of the first voltage source, the second bridge arm is connected in parallel on both sides of the first bridge arm, the central part of the first bridge arm is electrically connected to the central part of the second bridge arm through the first winding circuit of the three-winding transformer, the third winding circuit of the three-winding transformer is connected in parallel on both sides of the first voltage source, the second bridge arm is electrically connected to the second voltage source through the filtering circuit, and the second winding circuit of the three-winding transformer is connected in parallel on both sides of the second voltage source; the control ends of the first bridge arm and the second bridge arm are used for electrically connecting to the output end of the controller. The aim is to solve the problems in the existing soft-switching technical solutions, such as large current ripple or large reactive circulating current, resulting in large conduction losses and affecting efficiency.

Description

Technical Field

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

[0002] The high frequency of switching power supplies can reduce device size and weight, but it also increases switching losses. Currently, soft-switching technology is widely used to reduce switching losses. Existing soft-switching technologies for half-bridge bidirectional DC / DC converters mostly employ reverse current control, passive zero voltage switching (ZVS), and active zero voltage switching (ZVS) schemes. While these solutions are simple in structure, they suffer from high current ripple or high circulating reactive current, resulting in high conduction losses and reduced efficiency.

[0003] Reverse current control schemes, such as Figure 1 As shown, there is no need to add any auxiliary components. By simply changing the control strategy, the inductor current can flow in both directions, and the negative inductor current can be used to charge and discharge the buffer capacitor of the switching tube, thereby achieving ZVS turn-on of the switching tube; however, the current ripple of the inductor is very large, the device current stress is large, and the conduction loss is large.

[0004] Passive zero voltage (ZVS) solutions, such as Figure 2 As shown in the figure, the auxiliary soft-switching network consists of Co1, Co2, and lr. The resonant network generates a current ilr, which is injected into the bridge arm midpoint, creating the conditions for zero-voltage switching of k1 and k2. The injected current ilr must be sufficiently large to ensure soft switching. This increases the current stress on the switch. Furthermore, resonant energy is exchanged back and forth between the load and the resonant network, generating reactive circulating current. This increases conduction losses and hinders efficiency.

[0005] Active zero voltage (ZVS) solutions, such as Figure 3 As shown in Figure 1, the auxiliary soft-switching network consists of SS3, D, and I1. Before SS1 is turned on, SS3 is turned on first, creating a resonant network that generates current I1, which is injected into the bridge arm midpoint, creating the conditions for zero-voltage switching of SS1 and SS2. However, resonant energy is exchanged between the input power supply and the auxiliary network, forming a reactive circulating current.

[0006] In view of this, this application is filed. Summary of the Invention

[0007] The purpose of the present invention is to provide a soft switching circuit and device for a half-bridge bidirectional DC / DC converter, which can effectively solve the problems in existing soft switching technical solutions, such as large current ripple or large reactive circulating current, which lead to large conduction losses and affect efficiency.

[0008] The present invention discloses a soft-switching circuit for a half-bridge bidirectional DC / DC converter, which includes a first voltage source, a first bridge arm, a second bridge arm, a filter circuit, a second voltage source, and a three-winding transformer;

[0009] Wherein, the first bridge arm is connected in parallel on both sides of the first voltage source, the second bridge arm is connected in parallel on both sides of the first bridge arm, the central part of the first bridge arm is electrically connected to the central part of the second bridge arm through the first winding circuit, the third winding circuit is connected in parallel on both sides of the first voltage source, the second bridge arm is electrically connected to the second voltage source through the filter circuit, and the second winding circuit is connected in parallel on both sides of the second voltage source;

[0010] Wherein, the control ends of the first bridge arm and the second bridge arm are used for electrical connection with the output end of the controller.

[0011] Preferably, the first bridge arm includes a first auxiliary bridge arm switch and a second auxiliary bridge arm switch. The collector of the first auxiliary bridge arm switch is electrically connected to the positive pole of the first voltage source, the emitter of the first auxiliary bridge arm switch is electrically connected to the first end of the first winding circuit, the collector of the second auxiliary bridge arm switch is electrically connected to the first end of the first winding circuit, and the emitter of the second auxiliary bridge arm switch is electrically connected to the negative pole of the first voltage source.

[0012] Preferably, the second bridge arm includes a first main bridge arm switch and a second main bridge arm switch. The collector of the first main bridge arm switch is electrically connected to the positive pole of the first voltage source, the emitter of the first main bridge arm switch is electrically connected to the second end of the first winding circuit, the collector of the second main bridge arm switch is electrically connected to the second end of the first winding circuit, and the emitter of the second main bridge arm switch is electrically connected to the negative pole of the first voltage source.

[0013] Preferably, the filter circuit includes a resonant capacitor and a filter inductor. One end of the resonant capacitor is electrically connected to the negative pole of the second voltage source, 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 electrically connected to the positive pole of the second voltage source.

[0014] Preferably, the first winding circuit includes a resonant inductor and a first winding. One end of the resonant inductor is electrically connected to the emitter of the first auxiliary bridge arm switch, the other end of the resonant inductor is electrically connected to the same-named end of the first winding, and the different-named end of the first winding is electrically connected to the emitter of the first main bridge arm switch.

[0015] Preferably, the second winding circuit includes a second winding and a first diode. The opposite-named end of the second winding is electrically connected to the negative electrode of the second voltage source, the same-named end of the second winding is electrically connected to the positive electrode of the first diode, and the negative electrode of the first diode is electrically connected to the positive electrode of the second voltage source.

[0016] Preferably, the third winding circuit includes a third winding and a second diode. The same-named end of the third winding is electrically connected to the negative electrode of the first voltage source, the opposite-named end of the third winding is electrically connected to the positive electrode of the second diode, and the negative electrode of the second diode is electrically connected to the positive electrode of the first voltage source.

[0017] 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 transistors.

[0018] The present invention also provides a soft-switching device for a half-bridge bidirectional DC / DC converter, including a controller and the soft-switching circuit of the half-bridge bidirectional DC / DC converter as described in any one of the above. The output end of the controller is electrically connected to the control ends of the first bridge arm and the second bridge arm.

[0019] In summary, for the soft-switching circuit and device of the half-bridge bidirectional DC / DC converter provided in this embodiment, the first voltage source and the second voltage source are mutually output. When the power flows from the first voltage source to the second voltage source, the first voltage source is the input and the second voltage source is the output, and the circuit enters the buck mode. The duty cycle of the second bridge arm is the duty cycle of the system. The first bridge arm is turned on for a period of time before the second bridge arm is turned on. The resonant energy is mainly released to the second voltage source on the load side through the second winding circuit of the three-winding transformer, and the resonant energy directly reaches the load through one-time power transfer. When the power flows from the second voltage source to the first voltage source, the second voltage source is the input and the first voltage source is the output, and the circuit enters the boost mode. Its working principle is the same as the above buck mode, thus solving the problems in the existing soft-switching technical solutions, such as large current ripple or large reactive circulating current, resulting in large conduction losses and affecting efficiency. Description of the Drawings

[0020] Figure 1 It is a circuit and waveform schematic diagram of a reverse current control scheme in the prior art.

[0021] Figure 2 It is a circuit schematic diagram of a passive zero voltage (ZVS) scheme in the prior art.

[0022] Figure 3 It is a circuit schematic diagram of an active zero voltage (ZVS) scheme in the prior art.

[0023] Figure 4It is a circuit schematic diagram of the soft-switching circuit and its device of the half-bridge bidirectional DC / DC converter provided by the embodiment of the present invention.

[0024] Figure 5 It is an equivalent circuit schematic diagram of the buck mode of the soft-switching circuit and its device of the half-bridge bidirectional DC / DC converter provided by the embodiment of the present invention.

[0025] Figure 6 It is a schematic diagram of the principle waveform of the buck mode of the soft-switching circuit and its device of the half-bridge bidirectional DC / DC converter provided by the embodiment of the present invention.

[0026] Figure 7 It is an equivalent circuit schematic diagram of each stage of the buck mode of the soft-switching circuit and its device of the half-bridge bidirectional DC / DC converter provided by the embodiment of the present invention.

[0027] Figure 8 It is an equivalent circuit schematic diagram of the boost mode of the soft-switching circuit and its device of the half-bridge bidirectional DC / DC converter provided by the embodiment of the present invention. Specific Embodiments

[0028] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some but not all of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0029] The following provides a detailed description of specific embodiments of the present invention with reference to the accompanying drawings.

[0030] Please refer to Figure 4 , the first embodiment of the present invention provides a soft-switching circuit for a half-bridge bidirectional DC / DC converter, including a first voltage source U1, a first bridge arm 1, a second bridge arm 2, a filter circuit 3, a second voltage source U2, and a three-winding transformer T;

[0031] Among them, the first bridge arm 1 is connected in parallel on both sides of the first voltage source U1, the second bridge arm 2 is connected in parallel on both sides of the first bridge arm 1, the central part of the first bridge arm 1 is electrically connected to the central part of the second bridge arm 2 through the first winding circuit of the three-winding transformer T, the third winding circuit of the three-winding transformer T is connected in parallel on both sides of the first voltage source U1, the second bridge arm 2 is electrically connected to the second voltage source U2 through the filter circuit 3, and the second winding circuit of the three-winding transformer T is connected in parallel on both sides of the second voltage source U2;

[0032] Among them, the control ends of the first bridge arm 1 and the second bridge arm 2 are used for electrical connection with the output end of the controller.

[0033] Specifically, in this embodiment, the first voltage source U1 and the second voltage source U2 are mutually output, and the voltage value of the first voltage source U1 is greater than the voltage value of the second voltage source U2. When the power flows from the first voltage source U1 to the second voltage source U2, the first voltage source U1 is the input, the second voltage source U2 is the output, and the soft-switching circuit of the half-bridge bidirectional DC / DC converter enters the buck mode. When the power flows from the second voltage source U2 to the first voltage source U1, the second voltage source U2 is the input, the first voltage source U1 is the output, and the soft-switching circuit of the half-bridge bidirectional DC / DC converter enters the boost mode.

[0034] Please refer to Figure 5, in this embodiment, taking the low-voltage side as a battery as an example, the buck mode represents charging and the boost mode represents discharging; the first arm 1 includes a first auxiliary arm switch Sa1 and a second auxiliary arm switch Sa2. The collector of the first auxiliary arm switch Sa1 is electrically connected to the positive pole of the first voltage source U1, the emitter of the first auxiliary arm switch Sa1 is electrically connected to the first end of the first winding circuit of the three-winding transformer T, the collector of the second auxiliary arm switch Sa2 is electrically connected to the first end of the first winding circuit of the three-winding transformer T, and the emitter of the second auxiliary arm switch Sa2 is electrically connected to the negative pole of the first voltage source U1; the second arm 2 includes a first main arm switch S1 and a second main arm switch S2. The collector of the first main arm switch S1 is electrically connected to the positive pole of the first voltage source U1, the emitter of the first main arm switch S1 is electrically connected to the second end of the first winding circuit of the three-winding transformer T, the collector of the second main arm switch S2 is electrically connected to the second end of the first winding circuit of the three-winding transformer T, and the emitter of the second main arm switch S2 is electrically connected to the negative pole of the first voltage source. The first auxiliary arm switch Sa1, the second auxiliary arm switch Sa2, the first main arm switch S1, and the second main arm switch S2 can be NMOS transistors.

[0035] It should be noted that in other embodiments, other types of arm switches can also be used, which are not specifically limited here, but these solutions are all within the protection scope of the present invention.

[0036] In the buck mode, the first main arm switch S1 is the main control switch, the duty cycle of the first main arm switch S1 is defined as the duty cycle of the system, the parasitic diode of the second main arm switch S2 serves as the freewheeling diode Ds2, the first auxiliary arm switch Sa1 is the control switch, and the parasitic diode of the second auxiliary arm switch Sa2 serves as the freewheeling diode Dsa2. In order to achieve the soft-switching operation of the first main arm switch S1 and the second main arm switch S2, the first auxiliary arm switch Sa1 is turned on for a period of time before the first main arm switch S1 is turned on. In the buck mode, there is almost no current in the third winding circuit of the three-winding transformer T, and the resonant energy is mainly released to the load-side second voltage source U2 through the second winding circuit of the three-winding transformer T, and the resonant energy is directly transferred to the load through the primary power transfer.

[0037] Specifically, in this embodiment, the filter circuit 3 includes a resonant capacitor Cr and a filter inductor Lf. One end of the resonant capacitor Cr is electrically connected to the negative electrode of the second voltage source U2, 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 second voltage source U2. The first winding circuit of the three-winding transformer T includes a resonant inductor Lr and a first winding N1. One end of the resonant inductor Lr is electrically connected to the emitter of the first auxiliary bridge arm switch Sa1, the other end of the resonant inductor Lr is electrically connected to the same-named end of the first winding N1, and the different-named end of the first winding N1 is electrically connected to the emitter of the first main bridge arm switch S1. The second winding circuit of the three-winding transformer T includes a second winding N2 and a first diode Da1. The different-named end of the second winding N2 is electrically connected to the negative electrode of the second voltage source U2, the same-named end of the second winding N2 is electrically connected to the positive electrode of the first diode Da1, and the negative electrode of the first diode Da1 is electrically connected to the positive electrode of the second voltage source U2. The third winding circuit of the three-winding transformer T includes a third winding N3 and a second diode Da2. The same-named end of the third winding N3 is electrically connected to the negative electrode of the first voltage source U1, the different-named end of the third winding N3 is electrically connected to the positive electrode of the second diode Da2, and the negative electrode of the second diode Da2 is electrically connected to the positive electrode of the first voltage source U1.

[0038] Please refer to Figures 6 to 7 , in this embodiment, for the convenience of analyzing the soft-switching working principle, it is assumed that the filter inductor is large enough and its ripple component is ignored, and the current of the filter inductor can be approximated as a constant value; before time t0, the equivalent circuit is as shown in Figure 7 (a), and the current of the filter inductor continues to flow through the freewheeling diode of the second main bridge arm switch. At this time, the working state of the circuit is the same as that of the hard-switching buck.

[0039] Stage 1 [t0, t1], the equivalent circuit is as shown in Figure 7 (b). At time t0, the first auxiliary bridge arm switch Sa1 turns on in advance of the first main bridge arm switch S1, and the current of the resonant inductor Lr starts to linearly increase 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 still conducts; while the resonant inductor Lr stores energy, through the three-winding transformer T, the second auxiliary bridge arm switch Sa2 forms a forward-conversion working mode, and the input power supply directly supplies power to the load, that is, the second voltage source U2.

[0040] Stage 2 [t1, t2], the equivalent circuit is as shown in Figure 7As 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 softly turned off, and the resonant inductor Lr and the resonant capacitor Cr start the resonant process. At this time, the resonant frequency is greater than the switching frequency, the voltage of the resonant capacitor Cr gradually rises, and the voltage of the corresponding first main bridge arm switch S1 gradually decreases.

[0041] Stage 3 [t2, t3], the equivalent circuit is as Figure 7 As shown in (d), at time t2, the voltage of the first main bridge arm switch S1 drops to zero, the parasitic diode of the first main bridge arm switch S1 conducts, creating conditions for the zero-voltage turn-on of the first main bridge arm switch S1; the current of the resonant inductor Lr starts to linearly decrease until the current of the resonant inductor Lr is equal to the current of the filter inductor Lf. At this time, as long as a turn-on signal is given to the first main bridge arm switch S1 in this stage, the first main bridge arm switch S1 can achieve zero-voltage turn-on.

[0042] Stage 4 [t3, t4], the equivalent circuit is as Figure 7 As 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 conducts current, and the current of the resonant inductor Lr continues to decrease until the current of the resonant inductor Lr drops to zero. After that, disconnecting the first auxiliary bridge arm switch Sa1 can achieve the zero-current turn-off of the first auxiliary bridge arm switch Sa1 and the first diode Da2; if the actual reverse recovery characteristic of the first diode Da2 is considered, a short oscillation process will occur.

[0043] Stage 5 [t4, t5], the equivalent circuit is as Figure 7 As shown in (f), after time t4, the current of the resonant inductor Lr is 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.

[0044] Stage 6 [t5, t6], the equivalent circuit is as Figure 7As shown in (g), at time t5, the first main bridge arm switch S1 turns off. Due to the resonance of the resonant capacitor Cr, the voltage of the first main bridge arm switch S1 rises linearly, and the voltage of the freewheeling diode Ds2 of the corresponding second main bridge arm switch S2 drops linearly. The first main bridge arm switch S1 realizes zero-voltage turn-off. 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 conducts, 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 period.

[0045] Please refer to Figure 8 , in this embodiment, in the boost mode, the second main bridge arm switch S2 is the main control switch, the duty cycle of the second main bridge arm switch S2 is defined as the duty cycle of the system, the parasitic diode of the first main bridge arm switch S1 serves as the freewheeling diode, the second auxiliary bridge arm switch Sa2 is the control switch, and the parasitic diode Dsa2 of the first auxiliary bridge arm switch Sa1 serves as the freewheeling diode. In order to achieve the soft-switching operation of the first main bridge arm switch S1 and the second main bridge arm switch S2, the second auxiliary bridge arm switch Sa2 turns on for a period of time before the second main bridge arm switch S2 turns on. In the boost mode, there is almost no current in the second winding circuit of the three-winding transformer T, and the resonant energy is mainly released to the first voltage source U1 on the load side through the third winding circuit of the three-winding transformer T. The resonant energy is directly transferred to the load through the primary power transfer; among them, the soft-switching principle of the boost mode is the same as that of the aforementioned buck mode.

[0046] Through the analysis of the working states of each stage of the equivalent circuits of the above buck mode and boost mode, it can be seen that the soft-switching circuit of the half-bridge bidirectional DC / DC converter can directly transfer the resonant energy to the load through the three-winding transformer T, rather than exchanging it between the auxiliary network and the power supply side to form a reactive current loop, and at the same time realize the soft-switching operation of all switching devices in the original power circuit and the auxiliary resonant network; among them, the voltage and current stresses of each switch tube, diode in the soft-switching circuit of the half-bridge bidirectional DC / DC converter and the second bridge arm 2 do not increase due to the addition of the resonant circuit, and it has a higher power conversion efficiency.

[0047] The second embodiment of the present invention provides a soft-switching device for a half-bridge bidirectional DC / DC converter, including a controller and the soft-switching circuit of the half-bridge bidirectional DC / DC converter as described in any one of the above, and the output end of the controller is electrically connected to the control ends of the first bridge arm 1 and the second bridge arm 2.

[0048] The above is only the preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions falling within the concept of the present invention belong to the protection scope of the present invention.

Claims

1. A soft-switching circuit for a half-bridge bidirectional DC / DC converter, characterized in that, It includes a first voltage source, a first bridge arm, a second bridge arm, a filter circuit, a second voltage source, and a three-winding transformer; Among them, the first bridge arm is connected in parallel on both sides of the first voltage source, the second bridge arm is connected in parallel on both sides of the first bridge arm, the central part of the first bridge arm is electrically connected to the central part of the second bridge arm through a first winding circuit, the third winding circuit is connected in parallel on both sides of the first voltage source, the second bridge arm is electrically connected to the second voltage source through the filter circuit, and the second winding circuit is connected in parallel on both sides of the second voltage source; Among them, the control terminals of the first bridge arm and the second bridge arm are used to be electrically connected to the output terminal of the controller.

2. The soft-switching circuit of a half-bridge bidirectional DC / DC converter 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 collector of the first auxiliary bridge arm switch is electrically connected to the positive pole of the first voltage source, the emitter of the first auxiliary bridge arm switch is electrically connected to the first end of the first winding circuit, the collector of the second auxiliary bridge arm switch is electrically connected to the first end of the first winding circuit, and the emitter of the second auxiliary bridge arm switch is electrically connected to the negative pole of the first voltage source.

3. The soft-switching circuit of a half-bridge bidirectional DC / DC converter 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 collector of the first main bridge arm switch is electrically connected to the positive pole of the first voltage source, the emitter of the first main bridge arm switch is electrically connected to the second end of the first winding circuit, the collector of the second main bridge arm switch is electrically connected to the second end of the first winding circuit, and the emitter of the second main bridge arm switch is electrically connected to the negative pole of the first voltage source.

4. The soft-switching circuit of a half-bridge bidirectional DC / DC converter according to claim 1, wherein, The filter circuit includes a resonant capacitor and a filter inductor. One end of the resonant capacitor is electrically connected to the negative pole of the second voltage source, 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 electrically connected to the positive pole of the second voltage source.

5. The soft-switching circuit of a half-bridge bidirectional DC / DC converter according to claim 3, characterized in that, The first winding circuit includes a resonant inductor and a first winding. One end of the resonant inductor is electrically connected to the emitter of the first auxiliary bridge arm switch, the other end of the resonant inductor is electrically connected to the same-named end of the first winding, and the different-named end of the first winding is electrically connected to the emitter of the first main bridge arm switch.

6. The soft-switching circuit of a half-bridge bidirectional DC / DC converter according to claim 1, wherein, The second winding circuit includes a second winding and a first diode. The different-named end of the second winding is electrically connected to the negative pole of the second voltage source, the same-named end of the second winding is electrically connected to the positive pole of the first diode, and the negative pole of the first diode is electrically connected to the positive pole of the second voltage source.

7. The soft-switching circuit of a half-bridge bidirectional DC / DC converter according to claim 1, wherein, The third winding circuit includes a third winding and a second diode. The same-named end of the third winding is electrically connected to the negative pole of the first voltage source, the different-named end of the third winding is electrically connected to the positive pole of the second diode, and the negative pole of the second diode is electrically connected to the positive pole of the first voltage source.

8. The soft-switching circuit of a half-bridge bidirectional DC / DC converter 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 transistors.

9. A soft-switching device for a half-bridge bidirectional DC / DC converter, characterized in that, Comprising a controller and a soft-switching circuit of the half-bridge bidirectional DC / DC converter according to any one of claims 1 to 8, an output end of the controller is electrically connected to control ends of the first bridge arm and the second bridge arm.

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