A novel ZCS-PWM power-factor preregulator with reduced conduction losses

This paper proposes a new single-phase high-power-factor rectifier, which features regulation by conventional pulsewidth modulation (PWM), soft commutation, and instantaneous average line current control. A new zero-current-switching PWM (ZCS-PWM) auxiliary circuit is configured in the presented ZCS-PWM rectifier to perform ZCS in the active switches and zero-voltage switching in the passive switches. Furthermore, soft commutation of the main switch is achieved without additional current stress by the presented ZCS-PWM auxiliary circuit. A significant reduction in the conduction losses is achieved, since the circulating current for the soft switching flows only through the auxiliary circuit and a minimum number of switching devices are involved in the circulating current path and the proposed rectifier uses a single converter instead of the conventional configuration composed of a four-diode front-end rectifier followed by a boost converter. Nine transition states for describing the behavior of the ZCS-PWM rectifier in one switching period are described. The PWM switch model is used to predict the system performance. A prototype rated at I kW, operating 50 kHz, with an input ac voltage of 220 V-rms and an output voltage 400 V-dc has been implemented in laboratory. An efficiency of 97.3% and power factor over 0.99 has been measured. Analysis, design, and the control circuitry are also presented in this paper.