Input Power Factor Compensation for PWM-CSC Based High-Power Synchronous Motor Drives

An input power factor compensation scheme is proposed in this paper for pulse width modulated (PWM) current source converter (CSC) based medium-voltage high-power synchronous motor drives. At high-power levels, the device switching frequency in a PWM-CSC is normally limited to a few hundred hertz. This imposes limitations on the applicable PWM switching schemes and system control schemes. The proposed method can achieve full-range unity power factor control while operating at low switching frequency by combining inverter modulation index control and motor magnetizing current regulation. The modulation index control together with space vector modulation scheme is used in the low-speed range; at high speeds or whenever the converter runs out of modulation index adjustment, the magnetizing current control is enabled. Experimental results obtained from a 480V/42hp drive system verify the proposed scheme.