Research On The High-Frequency Variable Polarity Arc Welding Power Supply

In this thesis, a high-frequency variable polarity arc welding power supply was investigated, which consisted of two independent power sources, the variable polarity power supply and the high-frequency pulse one,having advantages both of them. The variable polarity power supply circuit uses two stages full-bridge inverter, the former inverter is regarded as a constant-current source with fast dynamic response, and supplys energy for the second one, and the latter one is to produce variable polarity current excellently, and low-frequency pulse current by variable polarity power supply is used to reduce input energy and control the shape of weld bead while welding. A series of high-frequency pulse current is superposed on Direct-Current-Electrode-Negative(DCEN) current through the high-frequency pulse power supply, which is used to compress the arc and improve process of crystallization.A system for the weld power source was established with Digital Signal Processor (DSP), and variable polarity power supply output, high-frequency pulse current, protection and process control were fulfilled with the software all, and modulate low frequency pulse current by means of amplitude modulation, through which it could also control the shape of weld seam like the low frequency pulse current welding. The mixed control chip SG3525A combined with hardware PI controller generates the high-frequency PWM pulse for the first inverter. The digital control block TMS320LF2407A mainly provides current preset for constant-current source through the outer filter, PWM pulse for the second inverter and drive signal for the high-frequency pulse power supply.At last, an experiential power supply was made, and a series of experiments is done. A lot of high-frequency pulse current was superposed on DCEN current, modulated the welding current waveform we required and optimized the energy distribution, which satisfied the basic requirement of cathode cleaning. Then the practical waveform was analyzed, and the results showed that this system work was stable and could meet the requirement of the design parameters.