Optimized Hybrid PWM Scheme for Mitigating Zero-Crossing Distortion in Totem-Pole Bridgeless PFC

A totem-pole bridgeless power factor corrector has been widely used in high-power ac-dc power conversion for its low component count and high energy efficiency. Its active bridge is configured to operate the power circuit as a synchronous boost converter over the line cycles. However, due to some intrinsic and extrinsic factors, input current distortion near the zero crossings is unavoidable. A hybrid pulsewidth modulation (PWM) scheme for mitigating such zero-crossing distortion is proposed. The concept is based on changing the PWM modulation schemes dynamically around the zero crossings, so that the line current can still be profiled with a switching scheme that does not require tracking the polarity of the grid voltage accurately. A generalized model for describing the variation of the inductor current, which is also the input current, from its average value in a switching cycle is formulated and is used to derive the optimal alignment of the PWM pulses for giving the smallest transient variation upon changing the modulation scheme. Results indicate that the voltage pulses generated by the active bridge are preferably symmetrical and center aligned in a switching period. A 1-kW 85-265-Vac/400-Vdc 47-63-Hz SiC-based prototype has been built and evaluated.