A new iterative learning control method for PWM inverter current regulation

AC servomotor speed or current controller based on PI control and/or optimal control, can not eliminate the cyclical fluctuations of speed or current when subject to periodic disturbances. PWM inverters output waveforms are distorted by dead-time effect, which is cyclical type disturbances. Conventional dead-time compensation methods based on feedforward techniques, using current reference polarity, do not resolve these effects around zero current crossing area. A new current regulation method based on iterative learning control technique is proposed in order to reduce the distortions caused by both the dead-time and the zero crossing problems.