Research Of Digitalized Variable Polarity TIG Welding Power Source

Digital inverter welding power source has become the developmental direction of welding machines to promote the great development of the welding industry, because of its high reliability, accuracy and flexible control and easily tending to be upgraded. Digital variable polarity power source possesses the cathode atomization effect and the outstanding merits of small tungsten burning, so it is the perfect welding method for welding aluminum alloy at the present time.AC arc need to restart arc at zero crossing, thus the stability of restrict arc is the most important performance of variable polarity arc. Based on a large number of relevant articles on the arc, the state of restrict arc was discussed to propose the relationship of arc voltage and time and welding current, devising a steady arc current to well solve the stability of variable polarity arc in small current condition.This paper introduces the development process of aluminum welding alloy and current research situation of variable polarity power source at home and abroad. The structure of main circuit implementation methods of second inverter was proposed: phase shift resonant soft-switching was adopted by first inverter topological structure, the whole bridge structure with series stable arc by second inverter. Simulation and comparison confirmed that soft-switching structure can effectively reduce consumption of power device. According to the welder input parameters, the primary components were calculated and selected by thermal phase diagram analysis, which were verified that the junction temperature of selected power modules meet the requirements.The "MCU+DSP" dual control system was adopted by control part. ATmega64L was chosen as the main chip of MCU to be responsible for the overall management of the system to give definite parameters and communicate with DSP and host computer and transmit data and display welding data in real time. MC56F8346 was chosen as the main chip of DSP to be responsible for the feedback of welding current and welding voltage, close loop PI algorithm and welding time sequence control, so that the good output performance of power source was certified.Data exchange through RS-485 protocol between the main control board and front panel by sampling speed opt coupler, solving the problem of the data transfer delay. A special filter circuit was designed to reduce the grid disturbance, passing a special EMC test to meet European standards.The PI regulation of welding parameters and precise control of welding process were implemented through software design. The system stability was improved by digital filtering software interference resist technology.Based on the waveform analysis of welding current and voltage, the influence of the variable polarity TIG welding power source waveform parameters on welding effect was discussed. Through the welding current and weld voltage waveform analysis with different parameters, test and practical application confirmed that the variable polarity welding power source can achieve good results.The deficiencies of this paper are as follows:AC arc model at zero crossing point was proposed, but it was only a preliminary study; the description of the arc model was not very accurate, requiring further study.