Unified Pulsewidth-Cycle Control Strategy to Achieve Mixed DCM/CRM Operation and Consistent Valley Switching for Boost PFC Converter

This article proposes a unified pulsewidth-cycle (UPWC) control strategy to achieve mixed-mode operation and consistent valley switching (VS) for boost power factor correction converter. Compared with conventional single-mode controllers, it has a unified scheme to achieve single discontinuous conduction mode (DCM), single critical conduction mode (CRM), or mixed DCM/CRM operations in each half-line cycle. To regulate the input current as a sinusoid, the UPWC controller adopts a variable pulsewidth and a near-constant switching cycle under DCM, while adopts a constant pulsewidth and a variable switching cycle under CRM. To facilitate analysis, normalized mapping of operation modes is provided, along with the final pulsewidth and switching cycle. Furthermore, to ensure consistent VS, a controlled zero current detection method is proposed to fix the turn-on point of the power switch. No matter in DCM or CRM, consistent VS reduces both the switching loss and current distortion caused by parasitic resonance. To further reduce the current distortion caused by fixing the turn-on point, a compensation gain is provided that reshapes the input current as a sinusoid. Finally, through mixed DCM/CRM operation and consistent VS, the proposed UPWC controller achieves preferable performances in the power range, efficiency, power factor, and current distortion.