Aiming at the instability of welding current caused by nonlinear change of load resistance in resistance spot welding process, a control algorithm combining fuzzy control and PI control is proposed. A PI controller with proportional coefficient and integral coefficient which is liable to realtime and online control is designed by using fuzzy control. The system model of medium frequency DC spot welding power supply is constructed. The PI control output can generate four PWM waves with constant duty cycle and realtime change of phase shift angle through PWM generator. The phaseshifting voltage regulation of full bridge inverter is realized. The welding of PI control and fuzzy PI control is compared by Simulink simulation. The simulation results show that before reaching the given current, the load current overshoot of PI control is large and the waveform oscillates; while the current of fuzzy PI control is almost no overshoot, the waveform is very stable and the adjustment speed is fast. When the load resistance changes, the load current of PI control oscillates and the system robustness is poor; the load current fluctuation of fuzzy PI algorithm is very small and the time to recover to the given value is short. Therefore, the fuzzy PI algorithm can effectively improve the stability of welding current and the dynamic performance of the system.
LI Yu-xin, WANG Bin. Research and Simulation of Constant Current Control Method for Medium Frequency DC Spot Welding Machine[J]. Journal of Chongqing Technology and Business University(Natural Science Edition）,2022,39(1):19-25