A charging pile solid state transformer topology for implementing single-phase ac-ac conversion

Abstract

The application provides a charging pile solid state transformer topology for realizing single-phase AC-AC conversion, and relates to the technical field of electronic transformers.The transformer topology comprises an alternating current power supply, a power frequency commutation rectifier circuit, a bidirectional direct current converter and a power frequency commutation inverter circuit; wherein the power frequency commutation rectifier circuit comprises a first H-bridge circuit; the power frequency commutation inverter circuit comprises a second H-bridge circuit; the first H-bridge circuit and the second H-bridge circuit are composed of bidirectional thyristors which switch the state according to the power frequency; the bidirectional direct current converter comprises a primary side direct current bus capacitor module, a first half-bridge circuit, an LC resonant circuit, a high-frequency transformer, a second half-bridge circuit and a secondary side direct current bus capacitor module.The overall topology structure directly couples the bidirectional direct current converter through the power frequency commutation H-bridge, reduces the intermediate links in the energy transmission path, reduces the number of devices and the system complexity, thereby improving the reliability of the system while reducing the cost.

Description

Technical Field

[0001] This invention relates to the field of electronic transformer technology, and in particular to a solid-state transformer topology for charging piles that realizes single-phase AC-AC conversion. Background Technology

[0002] Traditional power frequency transformers are not only large in size but also have relatively limited functions. With the rapid development of smart grids and the integration of various distributed energy sources, the functions of traditional power frequency transformers can no longer meet the requirements of modern power systems. Power electronic transformers, also known as solid-state transformers, intelligent transformers, or flexible transformers, are a new type of transformer that uses power electronics technology to achieve voltage transformation and energy transfer in power systems. Power electronic transformers are not only small in size and light in weight, but also have advantages such as highly controllable primary and secondary voltage, current, and power, and the ability to function as circuit breakers, eliminating the need for traditional transformer relay protection devices.

[0003] Current solid-state transformers come in many topologies, generally employing a multi-stage conversion structure including a rectifier stage, isolation stage, and inverter stage. This structure suffers from drawbacks such as a large number of fully controlled power switches, the need for large energy storage capacitors, high cost, low conversion efficiency, low power density, low reliability, and severe electromagnetic interference. Chinese invention patent CN110829876A discloses a single-phase solid-state transformer topology, consisting of an AC power supply, a first H-bridge circuit, a bidirectional DC-DC converter, a bidirectional buck circuit, and a second H-bridge circuit. This topology involves numerous components and complex circuitry. Furthermore, the third H-bridge and bidirectional buck circuit in the bidirectional DC-DC converter require high-frequency switching, resulting in high switching losses and low conversion efficiency. Summary of the Invention

[0004] This invention provides a solid-state transformer topology for charging piles that realizes single-phase AC-AC conversion, in order to solve the problems of large number of solid-state transformer components, complex circuits, high switching losses, and low conversion efficiency.

[0005] This invention provides a solid-state transformer topology for charging piles that realizes single-phase AC-AC conversion, including: an AC power supply, a power frequency commutation rectifier circuit, a bidirectional DC-DC converter, and a power frequency commutation inverter circuit; wherein, the power frequency commutation rectifier circuit includes a first H-bridge circuit; the power frequency commutation inverter circuit includes a second H-bridge circuit; the first H-bridge circuit and the second H-bridge circuit switch their switching states according to the power frequency; the bidirectional DC-DC converter includes a primary-side DC bus capacitor module, a first half-bridge circuit, an LC resonant circuit, a high-frequency transformer, a second half-bridge circuit, and a secondary-side DC bus capacitor module; The positive terminal of the AC power supply is connected to the first terminal of the first inductor; the first terminal of the first H-bridge circuit is connected to the second terminal of the first inductor, and the second terminal of the first H-bridge circuit is connected to the negative terminal of the AC power supply. The first terminal of the bidirectional DC-DC converter is connected to the third terminal of the first H-bridge circuit, and the second terminal of the bidirectional DC-DC converter is connected to the fourth terminal of the first H-bridge circuit; the third terminal of the second H-bridge circuit is connected to the third terminal of the bidirectional DC-DC converter, and the fourth terminal of the second H-bridge circuit is connected to the fourth terminal of the bidirectional DC-DC converter.

[0006] In this embodiment of the invention, the H-bridges on both the rectifier and inverter sides are composed of bidirectional thyristors capable of switching states according to the power frequency, reducing the number of fully controlled switching devices and simplifying the drive circuit design. Simultaneously, switching states at the power frequency reduce switching losses and electromagnetic interference. In the bidirectional DC-DC converter, bidirectional energy transfer is achieved through the coordinated operation of the first half-bridge, the LC resonant circuit, and the second half-bridge, combined with a high-frequency transformer. The LC resonant characteristics assist the half-bridge circuit in achieving zero-voltage or zero-current switching, further reducing switching losses and improving efficiency. The overall topology directly couples the bidirectional DC-DC converter through the power frequency commutated H-bridge, reducing intermediate links in the energy transfer path, lowering the number of devices and system complexity, thereby improving system reliability and reducing costs. Attached Figure Description

[0007] Figure 1 This is a schematic diagram of the solid-state transformer topology of a charging pile that realizes single-phase AC-AC conversion, provided by an embodiment of the present invention. Figure 2 The input voltage and output voltage waveforms of the bidirectional DC-DC converter provided in the embodiments of the present invention; Figure 3 The input voltage and output voltage waveforms are shown in the embodiments of the present invention. Figure 4 The input current and output current waveforms are shown in this embodiment of the invention. Detailed Implementation

[0008] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0009] Figure 1 This is a schematic diagram of the solid-state transformer topology for a charging pile that implements single-phase AC-AC conversion, provided by an embodiment of the present invention. Figure 1 The circuit includes: an AC power supply, a power frequency commutated rectifier circuit 10, a bidirectional DC-DC converter 20, and a power frequency commutated inverter circuit 30.

[0010] The power frequency commutation rectifier circuit 10 includes a first H-bridge circuit; the power frequency commutation inverter circuit 30 includes a second H-bridge circuit; the first H-bridge circuit and the second H-bridge circuit are composed of bidirectional thyristors that switch states according to the power frequency; the bidirectional DC-DC converter 20 includes a primary-side DC bus capacitor module, a first half-bridge circuit, an LC resonant circuit, a high-frequency transformer, a second half-bridge circuit, and a secondary-side DC bus capacitor module.

[0011] The first H-bridge circuit is composed of two sets of bidirectional thyristors connected in parallel, and the second H-bridge circuit is also composed of two sets of bidirectional thyristors connected in parallel.

[0012] The positive terminal of the AC power supply is connected to the first terminal of the first inductor; the first terminal of the first H-bridge circuit is connected to the second terminal of the first inductor, and the second terminal of the first H-bridge circuit is connected to the negative terminal of the AC power supply.

[0013] The first and second endpoints of the first H-bridge circuit are the midpoints of two sets of bidirectional thyristors connected in series. Similarly, the first and second endpoints of the second H-bridge circuit are the midpoints of two sets of bidirectional thyristors connected in series.

[0014] The first terminal of the bidirectional DC-DC converter 20 is connected to the third terminal of the first H-bridge circuit, and the second terminal of the bidirectional DC-DC converter 20 is connected to the fourth terminal of the first H-bridge circuit; the third terminal of the second H-bridge circuit is connected to the third terminal of the bidirectional DC-DC converter 20, and the fourth terminal of the second H-bridge circuit is connected to the fourth terminal of the bidirectional DC-DC converter 20.

[0015] The third and fourth terminals of the first H-bridge circuit are the parallel connection points of two sets of bidirectional thyristors connected in series.

[0016] The third and fourth terminals of the second H-bridge circuit are the parallel connection points of two sets of bidirectional thyristors connected in series.

[0017] In this embodiment of the invention, the H-bridges on both the rectifier and inverter sides are composed of bidirectional thyristors capable of switching states according to the power frequency, reducing the number of fully controlled switching devices and simplifying the drive circuit design. Simultaneously, switching states at the power frequency reduce switching losses and electromagnetic interference. In the bidirectional DC-DC converter, bidirectional energy transfer is achieved through the coordinated operation of the first half-bridge, the LC resonant circuit, and the second half-bridge, combined with a high-frequency transformer. The LC resonant characteristics assist the half-bridge circuit in achieving zero-voltage or zero-current switching, further reducing switching losses and improving efficiency. The overall topology adopts a single-stage conversion structure, which, compared to traditional multi-stage conversion structures, reduces the number of fully controlled switching devices, eliminates the need for large energy storage capacitors, and directly couples the bidirectional DC-DC converter via the power frequency commutated H-bridge, reducing intermediate links in the energy transfer path, simplifying control logic, reducing the number of devices and system complexity, thereby improving system reliability and reducing costs.

[0018] The first H-bridge circuit includes: a first switching transistor. S 1 First switching transistor S 1 Main terminal 1 and first inductor L p The second terminal connection; the second switching transistor S 2 Second switching transistor S 2 The main terminal 2 is respectively connected to the first switching transistor S 1 Main terminal 1 and first inductor L p The second terminal is connected; the third switch is connected. S 3 Third switching transistor S 3 The main terminal 2 is connected to the main terminal 2 of the first switching transistor; the fourth switching transistor S 4 Fourth switching transistor S 4 Main terminal 2 is connected to the third switching transistor respectively S 3 The main terminal 1 is connected to the negative terminal of the AC power supply, and the fourth switching transistor... S 4 Main terminal 1 and second switching transistor S 2 Connect to main terminal 1.

[0019] In the single-phase solid-state transformer topology of the above embodiments of the present invention, when power is transmitted in reverse: the first H-bridge circuit operates in inverter mode, and the current flows through the bidirectional thyristor to convert the input sinusoidal DC voltage into sinusoidal AC current.

[0020] The bidirectional DC-DC converter 20 includes: a primary-side linear bus capacitor module, and the first terminal of the primary-side linear bus capacitor module is connected to a third switching transistor. S 3 The main terminal 2 is connected, and the second terminal of the primary straight bus capacitor module is connected to the fourth switch. S 4The main terminal 1 is connected to: a first half-bridge circuit, the first terminal of which is connected to the first terminal of the primary straight bus capacitor module, and the second terminal of which is connected to the second terminal of the primary straight bus capacitor module; an LC resonant circuit, the first terminal of which is connected to the center terminal of the primary straight bus capacitor module, and the second terminal of which is connected to the center terminal of the first half-bridge circuit; a high-frequency transformer, the first terminal of the primary side of which is connected to the third terminal of the LC resonant circuit, and the second terminal of the primary side of which is connected to the fourth terminal of the LC resonant circuit; a second half-bridge circuit, the center terminal of which is connected to the first terminal of the secondary side of the high-frequency transformer; a secondary DC bus capacitor module, the first terminal of which is connected to the first terminal of the second half-bridge circuit, the second terminal of which is connected to the second terminal of the second half-bridge circuit, and the center terminal of which is connected to the second terminal of the secondary side of the high-frequency transformer.

[0021] The primary DC bus capacitor module includes: a first thin-film capacitor. C i First thin-film capacitor C i The first terminal and the third switch S 3 Main terminal 2 connection; second film capacitor C i Second thin-film capacitor C i The first terminal and the first thin film capacitor C i The second terminal is connected to the second thin-film capacitor. C i The second terminal and the fourth switch S 4 Connect to main terminal 1.

[0022] The first half-bridge circuit includes: a fifth switching transistor. S 5 Fifth switch tube S 5 The drain and the first thin film capacitor C i First terminal connection; sixth switch transistor S 6 The sixth switch S 6 The drain and the fifth switching transistor S 5 The source electrical connection, the sixth switch transistor S 6 The source and the second thin film capacitor C iThe second endpoint is connected.

[0023] The LC resonant circuit includes: a resonant inductor. L r resonant inductor L r The first terminal and the sixth switch S 6 Drain connection; Magnetizing inductor L m Magnetizing inductor L m The two ends are respectively connected to the resonant inductor L r The second endpoint and resonant capacitor C r The second terminal is connected; resonant capacitor C r resonant capacitor C r The first terminal and the second thin film capacitor C i The first endpoint is connected.

[0024] The high-frequency transformer includes: a primary winding, the first end of which is connected to the second end of the resonant inductor, and the second end of which is connected to the second end of the resonant capacitor; and a secondary winding, the first end of which is electrically connected to the source of the seventh switching transistor, and the second end of which is connected to the center end of the secondary DC bus capacitor module.

[0025] The second half-bridge circuit includes: a seventh switching transistor. S 7 Eighth switching transistor S 8 Eighth switch tube S 8 The drain and the seventh switch S 7 The source electrode connection; The secondary DC bus capacitor module includes: a third thin-film capacitor. C o Third thin-film capacitor C o The first terminal and the seventh switch S 7 Drain connection; fourth thin-film capacitor C o Fourth thin-film capacitor C o The first terminal and the third thin film capacitor C o The second terminal is connected to the fourth thin-film capacitor. C oThe second terminal and the eighth switch S 8 The source connection.

[0026] The topology of the single-phase solid-state transformer in the above embodiment of the present invention includes a bidirectional DC-DC converter 20, which is an LC series resonant converter. Both the primary and secondary sides employ a half-bridge structure, and the fully controlled power switching devices are N-channel enhancement-mode MOSFETs. The bidirectional DC-DC converter 20 operates in a natural bidirectional DCX mode, i.e., the resonant frequency equals the switching frequency, the voltage gain is fixed at 1, and the corresponding switches on the primary and secondary sides are simultaneously turned on and off. The bidirectional DC-DC converter 20 converts a sinusoidal DC voltage into a DC voltage with an absolute value of sine wave shape. u dc1 DC voltage transformed into the absolute value shape of a sine wave after electrical isolation u dc2 It can achieve voltage reduction. The high-frequency transformer can achieve electrical isolation between the primary and secondary sides and voltage amplitude adjustment. Through the high-frequency operation of the primary and secondary side switching transistors, the overall size of the solid-state transformer can be reduced. The bidirectional DC-DC converter 20 is a symmetrical half-bridge LLC, or other converters with equivalent functions such as asymmetrical half-bridge LLC, symmetrical full-bridge LLC, various CLLC converters, DAB converters, etc.; the fully controlled power switching devices of the bidirectional DC-DC converter 20 can also be IGBTs, IGCTs, BJTs with anti-parallel freewheeling diodes, or other switching devices with equivalent functions.

[0027] The second H-bridge circuit includes: a ninth switching transistor. S 9 Ninth switch S 9 Main terminal 2 and the third film capacitor C o First terminal connection; tenth switch transistor S 10 The tenth switch S 10 Main terminal 1 and the fourth film capacitor C o The second terminal is connected to the tenth switch. S 10 Main terminal 2 and the ninth switch transistor S 9 Main terminal 1 connection; Eleventh switch transistor S 11 Eleventh switch transistor S 11 Main terminal 2 and the ninth switch transistor S 9 Main terminal 2 connection; twelfth switch transistor S 12 The twelfth switch S12 Main terminal 2 of the tube and the eleventh switching tube S 11 Main terminal 1 connection, twelfth switch transistor S 12 Main terminal 1 is connected to main terminal 1 of the tenth switching transistor. First load R L First load R L The first endpoint is connected to the center point of the first arm of the second H-bridge circuit, and the first load R L The second endpoint is connected to the center point of the second bridge arm of the second H-bridge circuit.

[0028] In the single-phase solid-state transformer topology of the above embodiments of the present invention, when the first H-bridge circuit transmits power in the forward direction: the first H-bridge circuit operates in rectifier mode, and the current flows through the bidirectional thyristor, converting the input sinusoidal alternating current... u p Converted into a DC voltage with the absolute value of a sine wave. u dc1 The control method for the first H-bridge circuit is as follows: sample the input voltage, and when the sampled input voltage is positive, allow the first switching transistor to... S 1 and the fourth switching transistor S 4 Turn on; when the sampled input voltage is negative, turn on the second switching transistor. S 2 and the third switching transistor S 3 When the circuit is turned on, the input sinusoidal alternating current is converted into a direct current voltage with the absolute value of a sinusoidal wave. For example... Figure 2The diagram shows the input and output voltage waveforms of the bidirectional DC-DC converter provided in this embodiment of the invention. In the bidirectional DC-DC converter 20, during forward power transmission: the switching transistors of the first half-bridge of the bidirectional DC-DC converter 20 operate at high frequency, converting the sinusoidal absolute value DC voltage of the primary side DC bus into a high-frequency AC current with a sinusoidal envelope. This AC current is then coupled to the secondary side via a high-frequency transformer. The switching transistors in the second half-bridge circuit do not operate, and the high-frequency AC current is converted back to a sinusoidal absolute value DC voltage through uncontrolled rectification by the body diodes of the switching transistors or anti-parallel diodes. During reverse power transmission: the switching transistors in the second half-bridge circuit of the bidirectional DC-DC converter 20 operate at high frequency, converting the sinusoidal absolute value DC voltage of the secondary side DC bus into a high-frequency AC current with a sinusoidal envelope. This AC current is then coupled to the primary side via a high-frequency transformer. The switching transistors in the first half-bridge do not operate, and the high-frequency AC current is converted back to a sinusoidal absolute value DC voltage through uncontrolled rectification by the body diodes of the switching transistors or anti-parallel diodes. In the second H-bridge circuit, during forward power transmission: the second H-bridge circuit operates in inverter mode, with the bidirectional thyristors operating at power frequency, converting the input sinusoidal DC voltage into an absolute value shape. u dc2 It is converted into a sinusoidal alternating current output. u s The control method for the second H-bridge circuit is as follows: sample the input voltage, and when the sampled input voltage is positive, allow the ninth switch to... S 9 and the tenth switch S 10 Turn on; when the sampled input voltage is negative, turn on the eleventh switch. S 11 and the twelfth switch S 12 When the circuit is turned on, it converts the sinusoidal DC voltage into sinusoidal AC voltage. For example... Figure 3 The input voltage and output voltage waveforms are shown in the embodiments of the present invention. Figure 4 The input current and output current waveforms are shown in this embodiment of the invention.

[0029] In the single-phase solid-state transformer topology of the above embodiments of the present invention, when power is transmitted in reverse: the second H-bridge circuit operates in rectifier mode, and the current flows through the bidirectional thyristor to convert the sinusoidal alternating current into a DC voltage with the absolute value of a sinusoidal wave.

[0030] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A solid-state transformer topology for charging piles that realizes single-phase AC-AC conversion, characterized in that, include: The system comprises an AC power supply, a power frequency commutated rectifier circuit, a bidirectional DC-DC converter, and a power frequency commutated inverter circuit; wherein the power frequency commutated rectifier circuit includes a first H-bridge circuit; the power frequency commutated inverter circuit includes a second H-bridge circuit; the first H-bridge circuit and the second H-bridge circuit are composed of bidirectional thyristors that switch states according to the power frequency; the bidirectional DC-DC converter includes a primary-side DC bus capacitor module, a first half-bridge circuit, an LC resonant circuit, a high-frequency transformer, a second half-bridge circuit, and a secondary-side DC bus capacitor module; The positive terminal of the AC power supply is connected to the first terminal of the first inductor; the first terminal of the first H-bridge circuit is connected to the second terminal of the first inductor, and the second terminal of the first H-bridge circuit is connected to the negative terminal of the AC power supply. The first terminal of the bidirectional DC-DC converter is connected to the third terminal of the first H-bridge circuit, and the second terminal of the bidirectional DC-DC converter is connected to the fourth terminal of the first H-bridge circuit; the third terminal of the second H-bridge circuit is connected to the third terminal of the bidirectional DC-DC converter, and the fourth terminal of the second H-bridge circuit is connected to the fourth terminal of the bidirectional DC-DC converter.

2. The solid-state transformer topology for charging piles that realizes single-phase AC-AC conversion according to claim 1, characterized in that, The first H-bridge circuit includes: a first switch, a second switch, a third switch, and a fourth switch; Wherein, the main terminal 1 of the first switching transistor is connected to the second terminal of the first inductor; The main terminal 2 of the second switching transistor is connected to the main terminal 1 of the first switching transistor and the second terminal of the first inductor, respectively; The main terminal 2 of the third switch is connected to the main terminal 2 of the first switch. The main terminal 2 of the fourth switch is connected to the main terminal 1 of the third switch and the negative terminal of the AC power supply, respectively. The main terminal 1 of the fourth switch is connected to the main terminal 1 of the second switch.

3. The solid-state transformer topology for charging piles that realizes single-phase AC-AC conversion according to claim 2, characterized in that, The first terminal of the primary side straight bus capacitor module is connected to the main terminal 2 of the third switch transistor, and the second terminal of the primary side straight bus capacitor module is connected to the main terminal 1 of the fourth switch transistor. The first terminal of the first half-bridge circuit is connected to the first terminal of the primary side straight bus capacitor module, and the second terminal of the first half-bridge circuit is connected to the second terminal of the primary side straight bus capacitor module. The first terminal of the LC resonant circuit is connected to the center terminal of the primary straight bus capacitor module, and the second terminal of the LC resonant circuit is connected to the center terminal of the first half-bridge circuit. The first terminal of the primary side of the high-frequency transformer is connected to the third terminal of the LC resonant circuit, and the second terminal of the primary side of the high-frequency transformer is connected to the fourth terminal of the LC resonant circuit. The center endpoint of the second half-bridge circuit is connected to the first endpoint on the secondary side of the high-frequency transformer; The first terminal of the secondary DC bus capacitor module is connected to the first terminal of the second half-bridge circuit, the second terminal of the secondary DC bus capacitor module is connected to the second terminal of the second half-bridge circuit, and the center terminal of the secondary DC bus capacitor module is connected to the second terminal of the secondary side of the high-frequency transformer.

4. The solid-state transformer topology for charging piles that realizes single-phase AC-AC conversion according to claim 3, characterized in that, The primary side straight bus capacitor module includes: a first thin film capacitor and a second thin film capacitor; The first terminal of the first thin-film capacitor is connected to the main terminal 2 of the third switching transistor; The first terminal of the second film capacitor is connected to the second terminal of the first film capacitor, and the second terminal of the second film capacitor is connected to the main terminal 1 of the fourth switch.

5. The solid-state transformer topology for charging piles realizing single-phase AC-AC conversion according to claim 4, characterized in that, The first half-bridge circuit includes: The fifth switching transistor, the drain of which is connected to the first terminal of the first thin-film capacitor; The sixth switch is electrically connected to the source of the fifth switch, and the source of the sixth switch is connected to the second terminal of the second thin-film capacitor.

6. The solid-state transformer topology for charging piles realizing single-phase AC-AC conversion according to claim 5, characterized in that, The LC resonant circuit includes: a resonant inductor, a magnetizing inductor, and a resonant capacitor; The first terminal of the resonant inductor is connected to the drain of the sixth switching transistor; The two ends of the magnetizing inductor are respectively connected to the second terminal of the resonant inductor and the second terminal of the resonant capacitor; The first terminal of the resonant capacitor is connected to the first terminal of the second thin-film capacitor.

7. The solid-state transformer topology for charging piles realizing single-phase AC-AC conversion according to claim 6, characterized in that, The high-frequency transformer includes: a primary winding and a secondary winding; The first terminal of the primary winding is connected to the second terminal of the resonant inductor, and the second terminal of the primary winding is connected to the second terminal of the resonant capacitor; The first end of the secondary winding is electrically connected to the source of the seventh switching transistor, and the second end of the secondary winding is connected to the center point of the secondary DC bus capacitor module.

8. The solid-state transformer topology for charging piles realizing single-phase AC-AC conversion according to claim 1, characterized in that, The second half-bridge circuit includes: a seventh switch and an eighth switch; The drain of the eighth switch is electrically connected to the source of the seventh switch.

9. The solid-state transformer topology for charging piles realizing single-phase AC-AC conversion according to claim 8, characterized in that, The secondary DC bus module includes: a third thin-film capacitor and a fourth thin-film capacitor; The first terminal of the third thin-film capacitor is connected to the drain of the seventh switching transistor; The first terminal of the fourth thin-film capacitor is connected to the second terminal of the third thin-film capacitor, and the second terminal of the fourth thin-film capacitor is connected to the source of the eighth switching transistor.

10. The solid-state transformer topology for charging piles realizing single-phase AC-AC conversion according to claim 9, characterized in that, The second H-bridge circuit includes: a ninth switch, a tenth switch, an eleventh switch, a twelfth switch, and a first load; The main terminal 2 of the ninth switch is connected to the first terminal of the third thin film capacitor; The main terminal 1 of the tenth switch is connected to the second terminal of the fourth film capacitor, and the main terminal 2 of the tenth switch is connected to the main terminal 1 of the ninth switch. The main terminal 2 of the eleventh switch is connected to the main terminal 2 of the ninth switch. The main terminal 2 of the twelfth switch is connected to the main terminal 1 of the eleventh switch, and the main terminal 1 of the twelfth switch is connected to the main terminal 1 of the tenth switch. The ninth and tenth switches are connected in series to form the first bridge arm of the second H-bridge circuit; the eleventh and twelfth switches are connected in series to form the second bridge arm of the second H-bridge circuit. The first terminal of the first load is connected to the center point of the first arm of the second H-bridge circuit, and the second terminal of the first load is connected to the center point of the second arm of the second H-bridge circuit.

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