Research On VPTIG Welding Power Supply Based On SiC Module

The new generation of lightweight materials represented by magnesium alloys and aluminum alloys have the characteristics of low density,renewability,and good specific strength,specific stiffness,shock absorption and thermal conductivity,but these materials are usually extremely active and have a large expansion coefficient,resulting in poor welding performance.The variable polarity tungsten inert gas(Variable Polarity TIG,VPTIG)welding process has the effect of cathode atomization,and plays an important role in the lightweight alloy welding process.At present,the VPTIG welding power source on the market has problems such as low control accuracy,slow response speed,excessive heat input,slow speed of the zero crossing point of variable polarity,and easy arc breaking.As a wide bandgap semiconductor device,SiC-based power modules have lower on-state resistance,shorter switching delay time and switching time,and lower switching losses than Si-based IGBT,making them more suitable for high-frequency and high-power inverter application scenarios.The use of SiC-based power modules is more conducive to improving the comprehensive performance of the welding power system,and promoting the development of the welding power system to high frequency,efficiency and precision.This article first analyzed the welding characteristics of magnesium alloys and reviewed the research progress of magnesium alloy welding.Aiming at the defects in the magnesium alloy VPTIG welding process,in order to improve the stability of the VPTIG welding power source,a set of magnesium alloy high-frequency inverter power source was designed.VPTIG welding power source,and the VPTIG welding process of magnesium alloy was studied.Based on the PLECS simulation software,the commutation mechanism of the SiC-based modules in the high-frequency inverter process was analyzed,the key components of the main circuit were selected and the parameters were calculated,and a set of VPTIG welding power source with dual inverter structure was designed.The front-stage high-frequency inverter circuit of the main circuit adopted SiC-based power modules,and the latter-stage low-frequency inverter circuit adopted IGBT modules;in view of the crosstalk and short-circuit problems of SiC-based power devices in full-bridge applications,a drive circuit for SiC-based power device with fast soft turn-off and short-circuit protection function and Miller clamp function was designed;Double-pulse test for SiC MOSFET was carried out,and the influence of drive circuit parameters on the switching characteristics of SiC-based devices was tested and analyzed,and the influence of SiC-based devices' own parameter differences on its switching characteristics was discussed;With the ARM(advanced RISC machines)control chip as the core,a fully digital power supply control system was constructed.Through digital PID high-efficiency control,precise control of the current waveform was achieved,and it could output direct current,pulsed current,variable polarity current and pulsed variable polarity current.Finally,the electrical performance of the developed VPTIG welding power source was tested,and a magnesium alloy VPTIG welding platform was built to explore the influence of various parameters of pulsed variable polarity current on magnesium alloy welding.The results showed that the developed VPTIG welding power source has high commutation efficiency,control accuracy and dynamic response capability.It can output pulsed variable polarity current waveform with adjustable parameters at all stages,and the output waveform is regular and has a fast zero crossing speed.The inverter frequency reaches 50 kHz,and the output current of the whole machine reaches 500 A level.By adjusting the parameters of the pulsed variable polarity output current waveform,the heat input of magnesium alloy welding and the cathode cleaning effect can be accurately controlled,and the excellent weld formation can be obtained.