中频直流点焊机恒流控制方法研究与仿真

Research and Simulation of Constant Current Control Method for Medium Frequency DC Spot Welding Machine

针对电阻点焊过程存在的负载电阻非线性变化而导致焊接电流不稳定的问题,提出了模糊控制和PI控制二者相结合的控制算法。利用模糊控制设计了比例系数和积分系数可以实时在线整定的PI控制器,构建了中频直流点焊电源的系统模型,使PI控制输出量通过PWM发生器产生4路占空比恒定而移相角实时变化的PWM波,实现对全桥逆变器的移相调压,并通过Simulink仿真比较PI控制和模糊PI控制的焊接电流的动态特性。仿真结果表明:在达到电流给定之前,PI控制的负载电流超调大、波形出现振荡;而模糊PI控制的电流几乎没有超调、波形很平稳、调节速度快;当负载电阻变化时,PI控制的负载电流发生振荡、系统鲁棒性差;模糊PI算法的负载电流波动很小、恢复到给定值的时间短。由此,模糊PI算法能有效地提高焊接电流的稳定性和系统的动态性能。

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 real-time 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 real-time change of phase shift angle through PWM generator.The phase-shifting 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.