An on-line operated unity power factor PWM rectifier for AC drive applications

In order to minimize their impact on the AC supply, AC drives often require an input rectifier stage with low input current harmonics and high input power factor. High efficiency is also desirable. Drawbacks of the conventional off-line operated PWM rectifiers include slow transient response, load dependent input power factor and the need for damping resistors to avoid harmonic amplification and current oscillations, particularly under transient conditions. In this paper, an on-line operated PWM rectifier with inherent damping and pattern synchronization with the AC mains is proposed. Since the modulation scheme uses the voltages across the input filter capacitors as templates, faster transient response is achieved under normal and starting conditions and the need of the damping resistors is eliminated. Moreover, an additional phase-shifting circuit is used in the control scheme to achieve unity power factor, independently of the DC link current variations. The paper includes analysis and design guidelines for the rectifier control circuit. Experimental results on a 1 kVA laboratory prototype confirm the feasibility of the proposed control structure