Two-stage conversion asymmetric bipolar pulse micro-arc oxidation power supply

Abstract

The invention discloses a two-stage conversion asymmetric bipolar pulse micro-arc oxidation power supply, which comprises a first-stage conversion module, a second-stage conversion module and a full-bridge inversion module, and is characterized in that the first-stage conversion module is connected with the second-stage conversion module, and the second-stage conversion module is connected with the full-bridge inversion module, the first-stage conversion module is used for converting input alternating current into high-voltage direct current, the second-stage conversion module is used for converting the high-voltage direct current into low-voltage direct current, and the full-bridge inversion module is used for converting the low-voltage direct current into bipolar pulses. The system can meet the requirement of large-scale industrial production, and is high in control precision, fast in dynamic response, small in output loss, low in cost and high in system reliability.

Description

Technical Field

[0001] The invention relates to the technical field of micro-arc oxidation power supplies, and in particular to a two-stage conversion asymmetric bipolar pulse micro-arc oxidation power supply. Background Art

[0002] Micro-arc oxidation technology is one of the current research hotspots of material surface modification technology. It can grow a ceramic film with excellent performance on the surface of metal materials. With the development of micro-arc oxidation surface treatment technology, many new requirements have been put forward for high-power micro-arc oxidation power supplies suitable for industry. The use of asymmetric positive and negative bipolar AC power supplies can optimize the performance of the micro-arc oxidation layer while effectively saving energy.

[0003] However, the traditional high-power bipolar micro-arc oxidation power supply adopts a dual DC power supply plus inverter module design. The 1200V and 300V voltages are provided by two independent DC power supplies. The whole set of equipment is costly and complex in structure, which cannot meet the needs of large-scale industrial production. In addition, the small experimental power supply adopts a single DC power supply plus inverter module design, and meets the requirements of the micro-arc oxidation power supply for 1200V and 300V through an additional discharge circuit. This solution has high energy consumption, poor system response speed, and small power capacity, and is not suitable for use in industrial scenarios. Summary of the invention

[0004] The purpose of the present invention is to solve the above-mentioned technical problems and provide a two-stage conversion asymmetric bipolar pulse micro-arc oxidation power supply, which can be suitable for large-scale industrial production needs, has high control accuracy, fast dynamic response, small output loss, low cost and high system reliability.

[0005] In order to solve the above problems, the present invention is implemented according to the following technical solutions:

[0006] The present invention provides a two-stage conversion asymmetric bipolar pulse micro-arc oxidation power supply, comprising:

[0007] A first-stage conversion module, the first-stage conversion module includes an uncontrolled rectifier circuit, a high-frequency inverter circuit, a diode rectifier circuit and a first filter circuit, the uncontrolled rectifier circuit is connected to the high-frequency inverter circuit, the high-frequency inverter circuit is connected to the diode rectifier circuit, and the diode rectifier circuit is connected to the first filter circuit;

[0008] A second-stage conversion module, the second-stage conversion module is connected to the first-stage conversion module, and the second-stage conversion module includes a three-level step-down circuit;

[0009] A full-bridge inverter module, the full-bridge inverter module is connected to the second-stage conversion module, and the full-bridge inverter module includes a full-bridge inverter circuit;

[0010] Among them, the first-stage conversion module is used to convert the input AC power into high-voltage DC power, the second-stage conversion module is used to convert the high-voltage DC power into low-voltage DC power, and the full-bridge inverter module is used to convert the low-voltage DC power into bipolar pulses.

[0011] Preferably, the high-frequency inverter circuit includes a first insulated gate bipolar transistor, a second insulated gate bipolar transistor, a third insulated gate bipolar transistor, a fourth insulated gate bipolar transistor and a high-frequency transformer; wherein the emitter of the first insulated gate bipolar transistor is connected to the collector of the second insulated gate bipolar transistor, the emitter of the third insulated gate bipolar transistor is connected to the collector of the fourth insulated gate bipolar transistor, the emitter of the first insulated gate bipolar transistor is connected to the primary side of the high-frequency transformer, the emitter of the third insulated gate bipolar transistor is connected to the primary side of the high-frequency transformer, and the secondary side of the high-frequency transformer is connected to the diode rectifier circuit.

[0012] Preferably, the diode rectifier circuit includes a first diode and a second diode; wherein the anode of the first diode and the anode of the second diode are respectively connected to the two ends of the secondary side of the high-frequency transformer, the cathode of the first diode is connected to the cathode of the second diode, and the cathode of the first diode is connected to the first filter circuit.

[0013] Preferably, the first filtering circuit includes a first inductor and a first capacitor; one end of the first inductor is connected to the cathode of the first diode, and the other end of the first inductor is connected to the first capacitor.

[0014] Preferably, the three-level step-down circuit includes a second capacitor, a third capacitor, a fifth insulated gate bipolar transistor, a sixth insulated gate bipolar transistor, a third diode and a fourth diode; wherein the second capacitor is connected in series with the third capacitor, the collector of the fifth insulated gate bipolar transistor is connected to the second capacitor, the emitter of the fifth insulated gate bipolar transistor is connected to the negative electrode of the third diode, the emitter of the sixth insulated gate bipolar transistor is connected to the third capacitor, the collector of the sixth insulated gate bipolar transistor is connected to the positive electrode of the fourth diode, and the positive electrodes of the three diodes are connected to the negative electrode of the fourth diode.

[0015] Preferably, the three-level buck circuit further includes a second inductor and a fourth capacitor, the second inductor is connected to the cathode of the third diode, and the fourth capacitor is connected to the anode of the fourth diode; wherein the second inductor and the fourth capacitor are connected in series to form a second filtering circuit.

[0016] Preferably, the full-bridge inverter circuit includes a seventh insulated gate bipolar transistor, an eighth insulated gate bipolar transistor, a ninth insulated gate bipolar transistor and a tenth insulated gate bipolar transistor, the emitter of the seventh insulated gate bipolar transistor is connected to the collector of the eighth insulated gate bipolar transistor, the emitter of the seventh insulated gate bipolar transistor is connected to a load, the collector of the seventh insulated gate bipolar transistor is connected to the collector of the ninth insulated gate bipolar transistor, the emitter of the ninth insulated gate bipolar transistor is connected to the load, the emitter of the ninth insulated gate bipolar transistor is connected to the collector of the tenth insulated gate bipolar transistor, and the emitter of the tenth insulated gate bipolar transistor is connected to the emitter of the eighth insulated gate bipolar transistor.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] The present invention provides a two-stage conversion asymmetric bipolar pulse micro-arc oxidation power supply. On the one hand, a three-level step-down circuit is used to perform two-stage conversion of a DC voltage. While reducing the voltage stress of an insulated gate bipolar transistor, a higher switching frequency can be used for high-frequency chopping control, thereby achieving high-speed and high-precision asymmetric bipolar AC output. The power supply has the advantages of large power capacity, high control accuracy, fast dynamic response, small output loss and low overall cost, and can be suitable for large-scale industrial production applications.

[0019] In addition, the design of asymmetric bipolar pulse single power supply allows the power supply control to be performed in the same chip, and through the synchronous control of the two-stage DC source conversion and inverter module, more precise constant current and constant voltage output control is achieved. No external communication synchronization circuit is required, which improves the reliability of the system and reduces the cost of the equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The specific embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings, wherein:

[0021] Figure 1 It is a principle block diagram of a two-stage conversion asymmetric bipolar pulse micro-arc oxidation power supply of the present invention;

[0022] Figure 2 It is a circuit structure diagram of a two-stage conversion asymmetric bipolar pulse micro-arc oxidation power supply of the present invention;

[0023] Figure 3 It is a circuit structure diagram of the first-stage conversion module of a two-stage conversion asymmetric bipolar pulse micro-arc oxidation power supply of the present invention;

[0024] Figure 4 It is a circuit structure diagram of the second-stage conversion module of a two-stage conversion asymmetric bipolar pulse micro-arc oxidation power supply of the present invention;

[0025] Figure 5 It is a circuit structure diagram of a full-bridge inverter module of a two-stage conversion asymmetric bipolar pulse micro-arc oxidation power supply of the present invention;

[0026] In the figure:

[0027] S1-first insulated gate bipolar transistor, S2-second insulated gate bipolar transistor, S3-third insulated gate bipolar transistor, S4-fourth insulated gate bipolar transistor, S5-fifth insulated gate bipolar transistor, S6-sixth insulated gate bipolar transistor, S7-seventh insulated gate bipolar transistor, S8-eighth insulated gate bipolar transistor, S9-ninth insulated gate bipolar transistor, S10-tenth insulated gate bipolar transistor;

[0028] D1-first diode, D2-second diode, D3-third diode, D4-fourth diode;

[0029] L1-first inductor, L2-second inductor;

[0030] C1-first capacitor, C2-second capacitor, C3-third capacitor, C4-fourth capacitor;

[0031] R-load. DETAILED DESCRIPTION

[0032] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme 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 only 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 creative work should fall within the scope of protection of the present invention.

[0033] The terms used in this application are only for the purpose of describing specific embodiments and are not intended to limit this application. Unless otherwise defined, the technical terms or scientific terms used in this specification should be understood by people with ordinary skills in the field to which this application belongs. The words "first", "second" and similar words used in this specification and claims do not indicate any order, quantity or importance, but are only used to distinguish different technical features.

[0034] The preferred embodiments of the present invention are described below in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0035] Figure 1 This is a principle block diagram of a two-stage conversion asymmetric bipolar pulse micro-arc oxidation power supply of the present invention. Figure 2This is a circuit diagram of a two-stage conversion asymmetric bipolar pulse micro-arc oxidation power supply of the present invention. Figure 3 This is a circuit diagram of the first-stage conversion module of a two-stage conversion asymmetric bipolar pulse micro-arc oxidation power supply of the present invention. Figure 4 This is a circuit diagram of the second-stage conversion module of a two-stage conversion asymmetric bipolar pulse micro-arc oxidation power supply of the present invention. Figure 5 The present invention is a circuit structure diagram of a full-bridge inverter module of a two-stage conversion asymmetric bipolar pulse micro-arc oxidation power supply.

[0036] like Figure 1 to Figure 5 As shown, the two-stage conversion asymmetric bipolar pulse micro-arc oxidation power supply of the present invention comprises a first-stage conversion module, a second-stage conversion module and a full-bridge inverter module. The second-stage conversion module is connected to the first-stage conversion module, and the full-bridge inverter module is connected to the second-stage conversion module.

[0037] Specifically, the first-stage conversion module includes an uncontrolled rectifier circuit, a high-frequency inverter circuit, a diode rectifier circuit and a first filter circuit. The uncontrolled rectifier circuit is connected to the high-frequency inverter circuit, the high-frequency inverter circuit is connected to the diode rectifier circuit, and the diode rectifier circuit is connected to the first filter circuit. The second-stage conversion module includes a three-level buck circuit, and the full-bridge inverter module includes a full-bridge inverter circuit. Among them, the first-stage conversion module is used to convert the input AC power into high-voltage DC power, the second-stage conversion module is used to convert the high-voltage DC power into low-voltage DC power, and the full-bridge inverter module is used to convert the low-voltage DC power into bipolar pulses.

[0038] It should be noted that the uncontrolled rectifier circuit is a circuit that converts alternating current (AC) into direct current (DC), and it does not contain any control element to adjust the amplitude of the output DC voltage. This circuit usually contains a rectifier element, such as a diode or a thyristor (SCR), which is used to control the direction of the current so that it flows in only one direction, thereby converting the alternating current into direct current. In the present invention, the input end of the uncontrolled rectifier circuit is connected to the AC power supply, and the AC power supply can be converted into a DC power supply. Then, by connecting the output end of the uncontrolled rectifier circuit to the input end of the first-stage conversion module, the output end of the first-stage conversion module outputs 1200V high-voltage direct current after conversion. The output end of the first-stage conversion module is connected to the input end of the second-stage conversion module, and the input 1200V high-voltage direct current is stepped down to 300V low-voltage direct current through a three-level buck circuit and LC filtering, and output through the output end of the second-stage conversion module. The output end of the second-stage conversion module is connected to the input end of the full-bridge inverter module, and the 300V low-voltage direct current is inverted and converted into a bipolar pulse through the full-bridge inverter module. The two-stage conversion asymmetric bipolar pulse micro-arc oxidation power supply of the present invention can be suitable for large-scale industrial production needs, with high control accuracy, fast dynamic response, small output loss, low cost and high system reliability.

[0039] In one embodiment, the high-frequency inverter circuit includes a first insulated gate bipolar transistor S1, a second insulated gate bipolar transistor S2, a third insulated gate bipolar transistor S3, a fourth insulated gate bipolar transistor S4 and a high-frequency transformer. The emitter of the first insulated gate bipolar transistor S1 is connected to the collector of the second insulated gate bipolar transistor S2, the emitter of the third insulated gate bipolar transistor S3 is connected to the collector of the fourth insulated gate bipolar transistor S4, the emitter of the first insulated gate bipolar transistor S1 is connected to the primary side of the high-frequency transformer, the emitter of the third insulated gate bipolar transistor S3 is connected to the primary side of the high-frequency transformer, and the secondary side of the high-frequency transformer is connected to the diode rectifier circuit.

[0040] It should be noted that the insulated gate bipolar transistor (IGBT) is a power electronic device that combines the high input impedance of MOSFET and the low on-state voltage drop of bipolar transistor (BJT). Insulated gate bipolar transistors have high voltage and current handling capabilities and can handle high voltages and large currents. IGBTs also have faster switching speeds, which helps to generate the required bipolar pulses. In addition, IGBTs can be turned on and off by simple voltage control, which facilitates accurate pulse width modulation. IGBTs have high reliability and are suitable for use in harsh industrial environments. In the present invention, by using IGBTs, precise control of pulse amplitude, frequency, and duty cycle can be achieved, thereby optimizing the micro-arc oxidation process and improving the quality of the film layer.

[0041] In one embodiment, the diode rectifier circuit includes a first diode D1 and a second diode D2. The anode of the first diode D1 and the anode of the second diode D2 are respectively connected to the two ends of the secondary side of the high-frequency transformer, the cathode of the first diode D1 is connected to the cathode of the second diode D2, and the cathode of the first diode D1 is connected to the first filter circuit.

[0042] It should be noted that the diode rectifier circuit has the advantages of simple structure, low cost, high efficiency, high reliability and easy maintenance, because the diode rectifier circuit consists of a diode and a load, and no complex control components are required. The diode rectifier circuit can efficiently perform AC to DC conversion, especially in a full-wave rectification configuration. The diode is a mature electronic component with high reliability and low failure rate. Due to its simple structure, fault diagnosis and maintenance of the diode rectifier circuit are relatively easy.

[0043] It should be noted that the micro-arc oxidation process requires a stable DC power supply to maintain a constant electric field strength so as to form a uniform oxide film on the surface of the workpiece. The high efficiency and reliability of the diode rectifier circuit help to ensure the long-term stable operation of the power supply system, and the low cost makes the two-stage conversion asymmetric bipolar pulse micro-arc oxidation power supply of the present invention very economical. In addition, the output voltage of the diode rectifier circuit of the present invention is further smoothed by the first filter circuit to reduce the pulsation of the output voltage, thereby improving the output quality of the power supply.

[0044] In one embodiment, the first filtering circuit includes a first inductor L1 and a first capacitor C1. One end of the first inductor L1 is connected to the cathode of the first diode D1, and the other end of the first inductor L1 is connected to the first capacitor C1.

[0045] It should be noted that the first filter circuit is an LC filter circuit, which is a passive filter composed of a first inductor L1 and a first capacitor C1 component, to filter out unnecessary signal frequency components and only allow signals within a specific frequency range to pass. In the two-stage conversion asymmetric bipolar pulse micro-arc oxidation power supply design of the present invention, the LC filter circuit mainly smoothes the DC output voltage, reduces voltage ripple, improves the stability and output quality of the power supply, thereby improving the efficiency of the micro-arc oxidation process and the quality of the oxide film.

[0046] In one embodiment, the three-level step-down circuit includes a second capacitor C2, a third capacitor C3, a fifth insulated gate bipolar transistor, a sixth insulated gate bipolar transistor S6, a third diode D3 and a fourth diode D4. The second capacitor C2 is connected in series with the third capacitor C3, the collector of the fifth insulated gate bipolar transistor is connected to the second capacitor C2, the emitter of the fifth insulated gate bipolar transistor is connected to the cathode of the third diode D3, the emitter of the sixth insulated gate bipolar transistor S6 is connected to the third capacitor C3, the collector of the sixth insulated gate bipolar transistor S6 is connected to the anode of the fourth diode D4, and the anodes of the three diodes are connected to the cathode of the fourth diode D4.

[0047] It should be noted that the three-level buck circuit refers to the three-level BUCK circuit, which is a three-level buck switching power supply (Buck Converter) design. In power electronics, Buck Converter is a DC-DC converter used to reduce the input voltage to a lower output voltage. The three-level Buck Converter improves efficiency and reduces switching losses by using three levels (instead of the traditional two levels) to control the switch. The main features of the three-level Buck include higher efficiency, lower switching losses, smaller output ripple, smoother current waveform, and less electromagnetic interference (EMI). By adding an intermediate level, the three-level Buck can reduce the voltage stress of the switching element, thereby reducing the switching loss. Due to the reduction in voltage stress, the loss of the switching element during the switching process is reduced. The three-level control can adjust the output voltage more finely, thereby reducing the output ripple. On the input side of the three-level Buck, the current waveform is smoother, reducing the harmonic content of the input current. The three-level Buck can reduce EMI at a specific frequency due to the wider distribution of the switching frequency.

[0048] In the present invention, a three-level Buck circuit uses three different voltage states during a switching process to reduce switching losses and improve efficiency.

[0049] In one embodiment, the three-level buck circuit further includes a second inductor L2 and a fourth capacitor C4, the second inductor L2 is connected to the cathode of the third diode D3, and the fourth capacitor C4 is connected to the anode of the fourth diode D4; wherein the second inductor L2 and the fourth capacitor C4 are connected in series to form a second filtering circuit for smoothing the output voltage and reducing voltage ripple.

[0050] In one embodiment, the full-bridge inverter circuit includes a seventh insulated gate bipolar transistor S7, an eighth insulated gate bipolar transistor S8, a ninth insulated gate bipolar transistor S9 and a tenth insulated gate bipolar transistor S10, the emitter of the seventh insulated gate bipolar transistor S7 is connected to the collector of the eighth insulated gate bipolar transistor S8, the emitter of the seventh insulated gate bipolar transistor S7 is connected to a load R, the collector of the seventh insulated gate bipolar transistor S7 is connected to the collector of the ninth insulated gate bipolar transistor S9, the emitter of the ninth insulated gate bipolar transistor S9 is connected to the load R, the emitter of the ninth insulated gate bipolar transistor S9 is connected to the collector of the tenth insulated gate bipolar transistor S10, and the emitter of the tenth insulated gate bipolar transistor S10 is connected to the emitter of the eighth insulated gate bipolar transistor S8.

[0051] The working principle of the two-stage conversion asymmetric bipolar pulse micro-arc oxidation power supply described in the present invention is as follows: the two-stage conversion asymmetric bipolar pulse micro-arc oxidation power supply includes a first-stage conversion module, a second-stage conversion module and a full-bridge inverter module. The input end of the first-stage conversion module is connected to the AC power supply, the output end of the first-stage conversion module is connected to the input end of the second-stage conversion module, the output end of the second-stage conversion module is connected to the input end of the full-bridge inverter module, and the output end of the full-bridge inverter module is connected to the load R. The input AC power supply is converted by the first-stage conversion module to obtain a 1200V high-voltage direct current, and then the 1200V high-voltage direct current is reduced to a 300V low-voltage direct current through the three-level step-down circuit and LC filtering of the second-stage conversion module, and finally the bipolar pulse is output through the full-bridge inverter module.

[0052] On the one hand, a three-level step-down circuit is used for secondary conversion of DC voltage, which reduces the voltage stress of the insulated gate bipolar transistor and allows a higher switching frequency to be used for high-frequency chopping control, thereby achieving high-speed and high-precision asymmetric bipolar AC output. It has the advantages of large power capacity, high control accuracy, fast dynamic response, small output loss and low overall cost, and can be suitable for large-scale industrial production applications.

[0053] In addition, the design of asymmetric bipolar pulse single power supply allows the power supply control to be performed in the same chip, and through the synchronous control of the two-stage DC source conversion and inverter module, more precise constant current and constant voltage output control is achieved. No external communication synchronization circuit is required, which improves the reliability of the system and reduces the cost of the equipment.

[0054] For other structures of the two-stage conversion asymmetric bipolar pulse micro-arc oxidation power supply described in this embodiment, refer to the prior art.

[0055] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Therefore, any modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the technical solution of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A two-stage conversion asymmetric bipolar pulse micro-arc oxidation power supply, characterized in that: include: A first-stage conversion module, the first-stage conversion module includes an uncontrolled rectifier circuit, a high-frequency inverter circuit, a diode rectifier circuit and a first filter circuit, the uncontrolled rectifier circuit is connected to the high-frequency inverter circuit, the high-frequency inverter circuit is connected to the diode rectifier circuit, and the diode rectifier circuit is connected to the first filter circuit; A second-stage conversion module, the second-stage conversion module is connected to the first-stage conversion module, and the second-stage conversion module includes a three-level step-down circuit; A full-bridge inverter module, the full-bridge inverter module is connected to the second-stage conversion module, and the full-bridge inverter module includes a full-bridge inverter circuit; Among them, the first-stage conversion module is used to convert the input AC power into high-voltage DC power, the second-stage conversion module is used to convert the high-voltage DC power into low-voltage DC power, and the full-bridge inverter module is used to convert the low-voltage DC power into bipolar pulses.

2. A two-stage conversion asymmetric bipolar pulse micro-arc oxidation power supply according to claim 1, characterized in that: The high-frequency inverter circuit includes a first insulated gate bipolar transistor, a second insulated gate bipolar transistor, a third insulated gate bipolar transistor, a fourth insulated gate bipolar transistor and a high-frequency transformer; Among them, the emitter of the first insulated gate bipolar transistor is connected to the collector of the second insulated gate bipolar transistor, the emitter of the third insulated gate bipolar transistor is connected to the collector of the fourth insulated gate bipolar transistor, the emitter of the first insulated gate bipolar transistor is connected to the primary side of the high-frequency transformer, the emitter of the third insulated gate bipolar transistor is connected to the primary side of the high-frequency transformer, and the secondary side of the high-frequency transformer is connected to the diode rectifier circuit.

3. A two-stage conversion asymmetric bipolar pulse micro-arc oxidation power supply according to claim 2, characterized in that: The diode rectifier circuit includes a first diode and a second diode; The anode of the first diode and the anode of the second diode are respectively connected to the two ends of the secondary side of the high-frequency transformer, the cathode of the first diode is connected to the cathode of the second diode, and the cathode of the first diode is connected to the first filtering circuit.

4. A two-stage conversion asymmetric bipolar pulse micro-arc oxidation power supply according to claim 3, characterized in that: The first filtering circuit includes a first inductor and a first capacitor; one end of the first inductor is connected to the cathode of the first diode, and the other end of the first inductor is connected to the first capacitor.

5. A two-stage conversion asymmetric bipolar pulse micro-arc oxidation power supply according to claim 1, characterized in that: The three-level step-down circuit includes a second capacitor, a third capacitor, a fifth insulated gate bipolar transistor, a sixth insulated gate bipolar transistor, a third diode and a fourth diode; Among them, the second capacitor is connected in series with the third capacitor, the collector of the fifth insulated gate bipolar transistor is connected to the second capacitor, the emitter of the fifth insulated gate bipolar transistor is connected to the cathode of the third diode, the emitter of the sixth insulated gate bipolar transistor is connected to the third capacitor, the collector of the sixth insulated gate bipolar transistor is connected to the anode of the fourth diode, and the anode of the three diodes is connected to the cathode of the fourth diode.

6. A two-stage conversion asymmetric bipolar pulse micro-arc oxidation power supply according to claim 5, characterized in that: The three-level buck circuit further includes a second inductor and a fourth capacitor, wherein the second inductor is connected to the cathode of the third diode, and the fourth capacitor is connected to the anode of the fourth diode; The second inductor and the fourth capacitor are connected in series to form a second filtering circuit.

7. A two-stage conversion asymmetric bipolar pulse micro-arc oxidation power supply according to claim 1, characterized in that: The full-bridge inverter circuit includes a seventh insulated gate bipolar transistor, an eighth insulated gate bipolar transistor, a ninth insulated gate bipolar transistor and a tenth insulated gate bipolar transistor, the emitter of the seventh insulated gate bipolar transistor is connected to the collector of the eighth insulated gate bipolar transistor, the emitter of the seventh insulated gate bipolar transistor is connected to a load, the collector of the seventh insulated gate bipolar transistor is connected to the collector of the ninth insulated gate bipolar transistor, the emitter of the ninth insulated gate bipolar transistor is connected to the load, the emitter of the ninth insulated gate bipolar transistor is connected to the collector of the tenth insulated gate bipolar transistor, and the emitter of the tenth insulated gate bipolar transistor is connected to the emitter of the eighth insulated gate bipolar transistor.

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