| The variable polarity plasma arc welding (VPPAW) technology has manyadvantages such as concentrated heat, welding from one side while welds from bothsides, and cathode cleaning action. It is especially suited for the welding of Al, Mg &their alloys. VPPAW technology is widely used in aerospace and aeronauticmanufacture industry. The VPPAW power supply transforms the electricity networkpower to variable polarity dissymmetry alternating current square waves that thewelding plasma arc need, and it is an important factor affecting to arc stability andweld quality.As several main parts in the development of a new type high-power VPPAWpower supply system, the power transform circuit, control system of the arc weldingpower resource and the integration of the arc welding system are expatiated in thisthesis.Based on inverter technology, the power transform circuit including main arcand pilot arc power supplies was established, it can adapt the dynamic change ofwelding arc load. The main arc resource adopted double inverter structures, theoperation frequency of the first inverter is 20 kHz and the maximum output currentis 500A. With the adopting of self-adjusting commutation control strategy andcorresponding snubber circuit in the second inverter, this power supply can not onlyguarantee the safety and reliability for high current output, but also keep the arcstable for low current out. Therefore, it can be used even when large current range isrequired.The control system of the arc welding power supply consists of two controllers;one is programmable for welding process and the other for power supply. Based onthe Pulse-Width Modulation Integrated circuit, the controller for power supply canrealize control on the none-load voltage. Also, protection and alarming circuits weredesigned to prevent the possible failures happening in welding process, such asover-current, over/below voltage, over heat, etc. By means of Hall sensors, doubleclosed loop control system that consists of feedback controls on both average currentand instantaneous current pulse was developed to precisely control the output currentduring welding process. The control system has high control precision and rapiddynamic response speed, and the reliability and stability of the power supply systemis therefore improved.Based on the foregoing work, a high-power VPPAW system was established,which is mainly composed of power supply, gas flow controller, wire feeder, plasmatorch and welding bench, etc. The effect of the VPPAW welding parameters on theweld quality was analyzed. In addition, welding experiments were carried out onaluminum alloy and stainless steel plates with this equipment. Experimental resultsshow that the developed VPPAW system has high reliability. It can fulfill actualwelding requests and has very wide applications.
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