A three-phase four-wire AVR with IP control under unipolar PWM operation

A three-phase four-wire AC voltage regulator (AVR) is proposed. The system consists of three independent modules; each includes its own AC chopper, LC filter and series transformer. The unipolar pulse width modulation (PWM) is used to achieve fast response. The compensation voltage, positive or negative, can be generated by simply controlling the duty cycle of the power switches. Consequently, variations of the utility voltage would be restrained. Through the fixed-point digital signal microcontroller, an integral-proportional (IP) controller is implemented using a fast sensing technique of the output voltage. A 30-kVA prototype is constructed and the experimental results show that the system is with fast response and efficiency. Moreover, the harmonic components of the inverter output voltage are reduced