CN210080919U

CN210080919U - High-low frequency energy conversion and composite circuit of fast-frequency pulse TIG welding power supply

Info

Publication number: CN210080919U
Application number: CN201920788792.1U
Authority: CN
Inventors: 王振民; 吴健文; 范文艳
Original assignee: South China University of Technology SCUT
Current assignee: South China University of Technology SCUT
Priority date: 2019-05-29
Filing date: 2019-05-29
Publication date: 2020-02-18
Anticipated expiration: 2029-05-29

Abstract

The utility model provides a high low frequency energy transform of fast pulse TIG welding power and combined circuit, its characterized in that: the device comprises a power frequency rectifying and filtering circuit, a pulse current main circuit, a base current main circuit, a high-frequency current modulation circuit and a control circuit; the pulse current main circuit comprises a SiC full-bridge inversion commutation module I, a high-frequency transformation module I and a SiC rectification smoothing module I which are sequentially connected; the fundamental current main circuit comprises a SiC full-bridge inversion commutation module II, a high-frequency transformation module II and a SiC rectification smoothing module II which are sequentially connected; and the power frequency rectification filter circuit is respectively connected with the SiC full-bridge inversion commutation module I and the SiC full-bridge inversion commutation module II. The circuit has high inversion frequency and low loss, can stably output regular fast-frequency pulse current waveforms of 20kHz and above, is favorable for improving the electric arc control effect, and ensures that the waveforms are regular, stable and undistorted.

Description

High-low frequency energy conversion and composite circuit of fast-frequency pulse TIG welding power supply

Technical Field

The utility model relates to a welding equipment technical field, more specifically say, relate to a high low frequency energy transform of fast pulse TIG welding power and combined circuit.

Background

Pulse TIG welding is widely applied by the advantages of stable electric arc, zero spatter, high welding quality and wide range of weldable metal, but the traditional pulse TIG welding has lower pulse frequency, non-concentrated electric arc energy and larger heat input, so that a larger heat affected zone and thick weld grains are caused, and the mechanical property of the weld is reduced. Aiming at the problems of the traditional pulse TIG welding, a more advanced fast-frequency pulse TIG welding method is provided at present. Because the high-frequency pulse current (20kHz and above) is added into the fast-frequency pulse TIG welding, an electromagnetic field generated by the fast-frequency current can shrink the electric arc to form a shrinking arc columnar electric arc similar to a plasma arc. Therefore, the fast-frequency pulse TIG welding can improve the electric arc contraction degree of the pulse TIG welding, improve the electric arc energy density and improve the electric arc stiffness.

In recent years, the fast frequency pulse TIG welding technology is the focus of research in the domestic pulse TIG welding field. In a fast-frequency pulse TIG welding system, a fast-frequency pulse TIG welding power supply provides energy for an electric arc, and the performance of the welding power supply is very important. However, a great gap exists between the industrialization level of domestic TIG welding power supply equipment and developed countries, IGBTs are mostly adopted as power devices of power supplies, but due to structural factors of the IGBTs, trailing current is generated after the IGBTs are turned off, the switching loss of the IGBTs is large, the inversion frequency of a circuit is limited, generally 20kHz is limited, and the integral machine is overlarge in size and low in control precision. On the other hand, the fast-frequency pulse TIG welding technology adds the modulation of high-frequency current, which can generate strong electromagnetic interference on a welding power supply, and particularly has stronger influence on a power semiconductor device, so that the problems of unstable and irregular welding current and poor control effect of high-frequency arc are easily caused. Therefore, the popularization and application of the fast-frequency pulse TIG welding technology in China are limited by a plurality of factors.

SUMMERY OF THE UTILITY MODEL

For overcoming the shortcoming and not enough among the prior art, the utility model aims to provide an inversion frequency is high, the loss is low, can stabilize the output 20kHz and above regular fast frequency pulse current waveform, be favorable to improving electric arc control effect, make the regular stable fast frequency pulse TIG welding power supply high low frequency energy conversion and the composite circuit of undistorted of waveform.

In order to achieve the above purpose, the utility model discloses a following technical scheme realizes: a high-low frequency energy conversion and composite circuit of a fast-frequency pulse TIG welding power supply is characterized in that: the device comprises a power frequency rectifying and filtering circuit, a pulse current main circuit, a base current main circuit, a high-frequency current modulation circuit and a control circuit; the power frequency rectifying and filtering circuit is connected with a three-phase alternating current input power supply;

the pulse current main circuit comprises a SiC full-bridge inversion commutation module I, a high-frequency transformation module I and a SiC rectification smoothing module I which are sequentially connected; the fundamental current main circuit comprises a SiC full-bridge inversion commutation module II, a high-frequency transformation module II and a SiC rectification smoothing module II which are sequentially connected; the power frequency rectification filter circuit is respectively connected with the SiC full-bridge inversion commutation module I and the SiC full-bridge inversion commutation module II;

the high-frequency current modulation circuit comprises a high-frequency modulation module and an anti-reverse-filling module which are sequentially connected; the high-frequency modulation module is connected with the SiC rectification smoothing module I, and the reverse filling prevention module is connected with an external arc load; and the second SiC rectification smoothing module is connected with an external arc load.

Preferably, the first SiC full-bridge inversion commutation module includes a SiC power switch tube M101, a SiC power switch tube M102, a SiC power switch tube M103, and a SiC power switch tube M104; the high-frequency transformation module I comprises a high-frequency transformer I T101; the SiC power switch tube M101, the SiC power switch tube M102, the SiC power switch tube M103 and the SiC power switch tube M104 form a full-bridge inverter circuit, and then are connected with the primary side of the high-frequency transformer I T101 through a blocking capacitor C109; the SiC power switch tube M101, the SiC power switch tube M102, the SiC power switch tube M103 and the SiC power switch tube M104 are respectively connected with a RC absorption circuit I in parallel;

the SiC rectification smoothing module comprises a rectifier diode VD101, a rectifier diode VD102 and an inductor L101; a first output end of the secondary side of the high-frequency transformer I T101 is connected with a third output end of the secondary side of the high-frequency transformer I T101 through a rectifier diode VD101 and a rectifier diode VD102 which are connected in sequence; the junction of the rectifying diode VD101 and the rectifying diode VD102 is connected with one end of the inductor L101; the other end of the inductor L101 and a second output end of a secondary side of the high-frequency transformer T101 are respectively used as output ends of the pulse current main circuit to be connected with the high-frequency modulation module.

In the pulse current main circuit, an alternating current input power supply is connected with a power frequency rectifying and filtering circuit and is converted into smooth direct current; direct current passes through a full-bridge inverter circuit formed by a SiC power switch tube M101, a SiC power switch tube M102, a SiC power switch tube M103 and a SiC power switch tube M104, two paths of PWM signals with complementary dead zones control two opposite-angle SiC power switch tubes to be simultaneously switched on or switched off at high frequency, and the direct current is converted into high-frequency alternating current; then, the high-frequency transformer T101 is used for electrical isolation, voltage transformation and power transmission; the direct current is converted into low-voltage smooth direct current through the SiC rectification smoothing module and is output to the high-frequency current modulation circuit.

Preferably, the SiC power switch tube M101, the SiC power switch tube M102, the SiC power switch tube M103 and the SiC power switch tube M104 form a full-bridge inverter circuit, and then are connected with the primary side of the first high-frequency transformer module through a blocking capacitor C109; the SiC power switch tube M101, the SiC power switch tube M102, the SiC power switch tube M103 and the SiC power switch tube M104 are respectively connected in parallel with a RC absorption circuit I, which means that:

the circuit also comprises a capacitor C101, a capacitor C102, a capacitor C103, a capacitor C104, a capacitor C109, a resistor R101, a resistor R102, a resistor R103 and a resistor R104;

after the SiC power switch tube M101 and the SiC power switch tube M103 are connected in series, the SiC power switch tube M102 and the SiC power switch tube M104 are connected in series to form a circuit, and the circuit are connected in parallel to a power frequency rectifying and filtering circuit; the capacitor C101 and the resistor R101 are connected in series and then connected to the SiC power switch tube M101 in parallel; the capacitor C102 and the resistor R102 are connected in series and then connected to the SiC power switch tube M102 in parallel; the capacitor C103 and the resistor R103 are connected in series and then connected to the SiC power switch tube M103 in parallel; the capacitor C104 and the resistor R104 are connected in series and then connected to the SiC power switch tube M104 in parallel; the junction of the SiC power switch tube M101 and the SiC power switch tube M103 is connected with a capacitor C109 in series and then is connected with a primary first input end of a first high-frequency transformation module; and the connection part of the SiC power switch tube M102 and the SiC power switch tube M104 is connected with the primary second input end of the first high-frequency transformation module.

Preferably, the SiC power switch tube M101 is further connected in parallel with a diode D101; the SiC power switch tube M102 is also connected with a diode D102 in parallel; the SiC power switch tube M103 is also connected with a diode D103 in parallel; the SiC power switch M104 is also connected in parallel with a diode D104.

Preferably, the circuit structure of the SiC full-bridge inversion commutation module ii is the same as that of the SiC full-bridge inversion commutation module i; the circuit structure of the high-frequency transformation module II is the same as that of the high-frequency transformation module I; and the circuit structure of the second SiC rectification and smoothing module is the same as that of the first SiC rectification and smoothing module. The structure and the principle of the fundamental current main circuit are the same as those of the pulse current main circuit, only the control mode is different, and the existing mode can be adopted as the control mode.

Preferably, the high-frequency modulation module comprises a modulation switch tube IGBT Q202 and a modulation switch tube IGBT Q201; the reverse-irrigation preventing module comprises a rectifier diode VD 201; the modulation switch tube IGBT Q201 is connected in parallel to the first SiC rectification smoothing module; the first SiC rectification smoothing module is connected with an external arc load through a modulation switching tube IGBT Q202 and a rectifier diode VD201 which are connected in sequence; the modulation switch tube IGBT Q202 is connected with a first peak voltage absorption module in parallel; and the modulation switch tube IGBT Q201 is connected with a second peak voltage absorption module in parallel.

Preferably, the first spike voltage absorption module comprises a capacitor C202, a resistor R202, a diode D204 and a diode D203; a circuit formed by connecting the resistor R202 and the capacitor C202 in parallel and then connecting the resistor R202 and the diode D204 in series is connected to the modulation switch tube IGBTQ202 in parallel; the diode D203 is connected in parallel with the modulation switch tube IGBT Q202;

the second spike voltage absorption module comprises a capacitor C201, a resistor R201, a diode D202 and a diode D201; a circuit formed by connecting a resistor R201 and a diode D202 in parallel and then connecting the resistor R with a capacitor C201 in series is connected to a modulation switching tube IGBT Q201 in parallel; the diode D201 is connected in parallel with the modulation switch tube IGBT Q201.

In the high-frequency current modulation circuit, low-voltage direct current output by a pulse current main circuit is input to a high-frequency modulation module formed by a modulation switching tube IGBT Q201 and a modulation switching tube IGBT Q202, two paths of complementary no-dead-zone PWM signals control the modulation switching tube IGBT Q201 and the modulation switching tube IGBT Q202 to be alternately switched on and off at the frequency of 20kHz or higher, the direct current is converted into high-frequency current, the high-frequency current passes through an anti-recharging module and then is superposed with the low-voltage direct current output by a fundamental current main circuit, and the superposed high-frequency pulse current is output to an external arc load; the peak voltage absorption module I and the peak voltage absorption module absorb peak voltages generated in the process of modulating the high-frequency current; the rectifier diode VD201 prevents direct current output by the fundamental current main circuit from flowing back to the pulse current main circuit through the internal resistance of the high-frequency current modulation circuit, and the influence on the accurate output control of a power supply is avoided.

The utility model discloses an inverter type direct current, pulse TIG welding power supply energy conversion and combined circuit, output current both can be the pulse current of fast frequently, also can be ordinary pulse current and direct current. The SiC power switch tube is rapidly switched on and off according to a preset time sequence to realize high-frequency direct current and alternating current conversion; two modulation switching tubes IGBT of the high-frequency modulation module are alternately switched at the frequency of 20kHz or higher, so that the modulation of high-frequency pulse current is realized; in a fast frequency pulse TIG welding power supply, the output voltage and current sampling feedback of two parallel pulse current main circuits and a fundamental current main circuit is independently controlled; the output current and voltage are respectively collected and subjected to signal conditioning at the output ends of the pulse current main circuit and the fundamental current main circuit, and after the output current and voltage are compared with a preset value, the on-off time of the SiC power switch tube is changed, the duty ratio regulation is realized, the required waveform output is obtained, and the closed-loop control is completed.

Compare current TIG welding power supply technique soon frequently, the utility model discloses a new generation power electronic power device based on SiC improves contravariant frequency to 200kHz, improves welding current control accuracy, strengthens high frequency channel arc control effect, the regular fast pulse current of stable output. In addition, the fast-frequency pulse TIG welding power supply developed by the SiC power switching tube greatly reduces the volume and the mass of the transformer due to the ultrahigh inversion frequency; meanwhile, the SiC power switching tube has high switching speed and extremely low switching loss, so that the ultrahigh frequency switching state work is realized, and the magnetic core material with extremely low iron loss is adopted, so that the size and the weight of magnetic devices such as a transformer and the like can be further reduced, the magnetic loss is reduced, and the electric energy conversion efficiency is improved. On the other hand, as the inversion frequency is improved, the loop time is shortened, the high-speed and precise regulation and control of the output current and the output voltage can be realized, the control effect on high-frequency arc in the fast-frequency pulse TIG welding process is improved, and the waveform of the welding current is controlled to be regular, stable and undistorted.

The utility model discloses high low frequency energy transform of fast pulse TIG welding power and one of combined circuit's key lie in high frequency current modulation circuit. The existing pulse current modulation circuit usually adopts a topological structure that a single power switch tube is connected in parallel with the output end of a power supply, and because the impedance of an arc load of a welding power supply is smaller than the internal resistance of a parallel IGBT, a part of output current flows into the arc load while the parallel IGBT is conducted, and a regular fast-frequency pulse current waveform cannot be output. To this problem, the utility model provides a high frequency current modulation circuit adopts interlocking type topological structure, and when modulation switch pipe IGBT Q201 switched on, modulation switch pipe IGBT Q202 of establishing ties was turn-offed on the output circuit, cuts off output current and flows into arc load's route. The modulation switch tube IGBT Q201 and the modulation switch tube IGBT Q202 are restricted with each other and switched alternately, and the output current of the pulse current main circuit is ensured to flow from the positive pole to the negative pole of the power supply through the modulation switch tube IGBT Q201. The modulation switch tube IGBT Q201 and the modulation switch tube IGBT Q202 of the interlock type topology are alternately switched at the frequency of 20kHz or higher, and the modulation of high-frequency pulse current is realized.

Compared with the prior art, the utility model has the advantages of as follows and beneficial effect:

1. the power switch devices of the circuit of the utility model all adopt the SiC power devices of the new generation of power electronic devices, the switching frequency is higher, the dynamic response speed is better, and the dynamic response capability of 20kHz frequency pulse current can reach 4.7 mus; the efficiency is high, the maximum efficiency reaches 90.6%, and the efficiency can be kept about 90% when the power reaches more than 3500W;

2. the circuit of the utility model is beneficial to enhancing the control effect of high frequency band electric arc, stably outputting regular fast frequency pulse current waveform of 20kHz and above, and the waveform is regular, stable and undistorted in the welding process;

3. the utility model discloses the circuit, high frequency current modulation circuit can enough absorb the sharp pulse overvoltage that high frequency pulse current modulation process produced effectively, can not destroy fast frequency pulse current basic waveform again, simple structure, and is with low costs, and the reliability is high.

Drawings

FIG. 1 is a circuit block diagram of a high and low frequency energy conversion and composite circuit of the fast frequency pulse TIG welding power supply of the present invention;

FIG. 2 is a circuit diagram of the overall topology of the high and low frequency energy conversion and recombination circuit of the fast frequency pulse TIG welding power supply of the present invention;

FIG. 3 is a circuit diagram of the pulse current main circuit in the high and low frequency energy conversion and composite circuit of the fast frequency pulse TIG welding power supply of the present invention;

fig. 4 is a circuit diagram of the high-low frequency energy conversion and high-high frequency current modulation circuit in the composite circuit of the fast-frequency pulse TIG welding power supply of the present invention.

Detailed Description

The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.

Examples

The structure of a high-low frequency energy conversion and composite circuit of a fast-frequency pulse TIG welding power supply of the embodiment is shown in figures 1 to 4; the device comprises a power frequency rectifying and filtering circuit, a pulse current main circuit, a base current main circuit, a high-frequency current modulation circuit and a control circuit; the power frequency rectifying and filtering circuit is connected with a three-phase alternating current input power supply.

The pulse current main circuit comprises a SiC full-bridge inversion commutation module I, a high-frequency transformation module I and a SiC rectification smoothing module I which are sequentially connected; the fundamental current main circuit comprises a SiC full-bridge inversion commutation module II, a high-frequency transformation module II and a SiC rectification smoothing module II which are sequentially connected; and the power frequency rectification filter circuit is respectively connected with the SiC full-bridge inversion commutation module I and the SiC full-bridge inversion commutation module II.

The SiC full-bridge inversion commutation module I comprises a SiC power switch tube M101, a SiC power switch tube M102, a SiC power switch tube M103 and a SiC power switch tube M104; the high-frequency transformation module I comprises a high-frequency transformer I T101; the SiC power switch tube M101, the SiC power switch tube M102, the SiC power switch tube M103 and the SiC power switch tube M104 form a full-bridge inverter circuit, and then are connected with the primary side of the high-frequency transformer I T101 through a blocking capacitor C109; the SiC power switch tube M101, the SiC power switch tube M102, the SiC power switch tube M103 and the SiC power switch tube M104 are respectively connected with a RC absorption circuit I in parallel;

Specifically, the first SiC full-bridge inversion commutation module further includes a capacitor C101, a capacitor C102, a capacitor C103, a capacitor C104, a capacitor C109, a resistor R101, a resistor R102, a resistor R103, and a resistor R104;

The SiC power switch tube M101 is also connected with a diode D101 in parallel; the SiC power switch tube M102 is also connected with a diode D102 in parallel; the SiC power switch tube M103 is also connected with a diode D103 in parallel; the SiC power switch M104 is also connected in parallel with a diode D104.

The SiC power switch tube M101, the SiC power switch tube M102, the SiC power switch tube M103 and the SiC power switch tube M104 in the SiC full-bridge inversion commutation module I are respectively connected with the SiC driving module, and the SiC driving module is connected with the control module so as to realize that the SiC power switch tube M101, the SiC power switch tube M102, the SiC power switch tube M103 and the SiC power switch tube M104 are respectively and rapidly switched on and off according to preset time sequences. The SiC driving module and the control module can adopt the prior art, for example, the SiC driving module adopts a SiC high-frequency driving module which is disclosed in detail in Chinese invention patent application of full-digital SiC inversion type multifunctional argon arc welding power supply based on DSC (publication number: 106392262B).

The circuit structure of the SiC full-bridge inversion commutation module II is the same as that of the SiC full-bridge inversion commutation module I; the circuit structure of the high-frequency transformation module II is the same as that of the high-frequency transformation module I; and the circuit structure of the second SiC rectification and smoothing module is the same as that of the first SiC rectification and smoothing module. The structure and principle of the fundamental current main circuit are the same as those of the pulse current main circuit.

The SiC driving module used for driving the SiC power switch tube in the SiC full-bridge inversion commutation module II can also be the same as the SiC driving module used for driving the SiC power switch tube in the SiC full-bridge inversion commutation module I; the two driving modules only have different output driving waveforms and time sequences; the drive waveforms and timing may be in conventional manner.

The high-frequency modulation module comprises a modulation switch tube IGBT Q202 and a modulation switch tube IGBT Q201; the reverse-irrigation preventing module comprises a rectifier diode VD 201; the modulation switch tube IGBT Q201 is connected in parallel to the first SiC rectification smoothing module; the first SiC rectification smoothing module is connected with an external arc load through a modulation switching tube IGBT Q202 and a rectifier diode VD201 which are connected in sequence; the modulation switch tube IGBT Q202 is connected with a first peak voltage absorption module in parallel; and the modulation switch tube IGBT Q201 is connected with a second peak voltage absorption module in parallel.

The first spike voltage absorption module comprises a capacitor C202, a resistor R202, a diode D204 and a diode D203; a circuit formed by connecting a resistor R202 and a capacitor C202 in parallel and then connecting the resistor R202 and a diode D204 in series is connected to a modulation switching tube IGBT Q202 in parallel; the diode D203 is connected in parallel with the modulation switch tube IGBT Q202;

A modulation switch tube IGBT Q202 and a modulation switch tube IGBT Q201 of the high-frequency modulation module are respectively connected with an IGBT driving module, and the IGBT driving module is connected with a control module so as to realize that the modulation switch tube IGBT Q202 and the modulation switch tube IGBT Q201 are respectively switched on and off according to preset time sequences. The IGBT driving module can adopt the prior art, for example, a high-frequency inversion driving module disclosed in detail in the Chinese invention patent application 'multifunctional digital wave control arc welding inversion power supply' (publication number: 103692056B).

The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be equivalent replacement modes, and all are included in the scope of the present invention.

Claims

1. A high-low frequency energy conversion and composite circuit of a fast-frequency pulse TIG welding power supply is characterized in that: the device comprises a power frequency rectifying and filtering circuit, a pulse current main circuit, a base current main circuit, a high-frequency current modulation circuit and a control circuit; the power frequency rectifying and filtering circuit is connected with a three-phase alternating current input power supply;

2. A high and low frequency energy conversion and recombination circuit for a fast frequency pulse TIG welding power supply according to claim 1, wherein: the SiC full-bridge inversion commutation module I comprises a SiC power switch tube M101, a SiC power switch tube M102, a SiC power switch tube M103 and a SiC power switch tube M104; the high-frequency transformation module I comprises a high-frequency transformer I T101; the SiC power switch tube M101, the SiC power switch tube M102, the SiC power switch tube M103 and the SiC power switch tube M104 form a full-bridge inverter circuit, and then are connected with the primary side of the high-frequency transformer I T101 through a blocking capacitor C109; the SiC power switch tube M101, the SiC power switch tube M102, the SiC power switch tube M103 and the SiC power switch tube M104 are respectively connected with a RC absorption circuit I in parallel;

3. A high and low frequency energy conversion and recombination circuit for a fast frequency pulse TIG welding power supply according to claim 2, wherein: the SiC power switch tube M101, the SiC power switch tube M102, the SiC power switch tube M103 and the SiC power switch tube M104 form a full-bridge inverter circuit, and then are connected with the primary side of the first high-frequency transformation module through a blocking capacitor C109; the SiC power switch tube M101, the SiC power switch tube M102, the SiC power switch tube M103 and the SiC power switch tube M104 are respectively connected in parallel with a RC absorption circuit I, which means that:

4. A high and low frequency energy conversion and recombination circuit for a fast frequency pulse TIG welding power supply according to claim 2, wherein: the SiC power switch tube M101 is also connected with a diode D101 in parallel; the SiC power switch tube M102 is also connected with a diode D102 in parallel; the SiC power switch tube M103 is also connected with a diode D103 in parallel; the SiC power switch M104 is also connected in parallel with a diode D104.

5. A high and low frequency energy conversion and recombination circuit for a fast frequency pulse TIG welding power supply according to claim 2, wherein: the circuit structure of the SiC full-bridge inversion commutation module II is the same as that of the SiC full-bridge inversion commutation module I; the circuit structure of the high-frequency transformation module II is the same as that of the high-frequency transformation module I; and the circuit structure of the second SiC rectification and smoothing module is the same as that of the first SiC rectification and smoothing module.

6. A high and low frequency energy conversion and recombination circuit for a fast frequency pulse TIG welding power supply according to claim 2, wherein: the high-frequency modulation module comprises a modulation switch tube IGBT Q202 and a modulation switch tube IGBT Q201; the reverse-irrigation preventing module comprises a rectifier diode VD 201; the modulation switch tube IGBT Q201 is connected in parallel to the first SiC rectification smoothing module; the first SiC rectification smoothing module is connected with an external arc load through a modulation switching tube IGBT Q202 and a rectifier diode VD201 which are connected in sequence; the modulation switch tube IGBT Q202 is connected with a first peak voltage absorption module in parallel; and the modulation switch tube IGBT Q201 is connected with a second peak voltage absorption module in parallel.

7. A high and low frequency energy conversion and recombination circuit for a fast frequency pulse TIG welding power supply according to claim 6, wherein: the first spike voltage absorption module comprises a capacitor C202, a resistor R202, a diode D204 and a diode D203; a circuit formed by connecting a resistor R202 and a capacitor C202 in parallel and then connecting the resistor R202 and a diode D204 in series is connected to a modulation switching tube IGBT Q202 in parallel; the diode D203 is connected in parallel with the modulation switch tube IGBT Q202;