An on-line operated near unity power factor PWM rectifier with minimum control requirements

Most PWM rectifiers use online PWM patterns which results in slow transient response. Damping resistors must be provided to avoid amplification of harmonics and current oscillations, especially during transient conditions. This results in reduced efficiency. In this paper, a current-source type PWM rectifier with online pattern generation and inherent pattern synchronization with the AC mains is proposed. The voltages across the input filter capacitors are chosen as the modulating signals. This results in a very fast starting and a much improved transient response. Also, the need of the damping resistors is eliminated due to the effective damping provided through the modulating of the capacitor voltages. Moreover, an additional phase-shifting circuit is added to the control scheme to achieve near unity power factor independent of the load variations. The paper includes analysis, design guidelines and experimental results on a 1 kVA laboratory prototype to confirm the theoretical considerations