Research on Dynamic Voltage Compensation Control Technology of PWM AC Chopper

The traditional high frequency PWM ac choppers are usually controlled with the rms control method and are incapable of coping with the voltage transient variation. A type of instantaneous voltage compensation control scheme of a PWM ac chopper is proposed in this paper to suppress the voltage transient variations. The proposed control scheme consists of an output voltage rms control loop and an instantaneous fed-forward compensation path added to the rms control loop. Implemented with an MCU ATmega128, the RMS voltage mean value of the ac chopper is controlled by a digital PID regulator and the instantaneous voltage value is compensated by the repetitive control method. A laboratorial prototype is constructed and the Experimental results show that the proposed control scheme of the ac chopper is effective to suppress the output voltage transient variation caused by both the power grid voltage transient variation and the load sudden change. As a result, the ac chopper can be used as a dynamic voltage restorer.