Mirror-Bridge Phase-Shift Modulation With Low Common-Mode Noise for Single-Phase CHB PFC

For ac/dc power conversion applications like server power supply, telecom power supply, and on-board charger of an electric vehicle, the rising electricity demand has presented challenges toward high efficiency and high power density. The cascaded H-bridge (CHB) based multilevel power factor correction (PFC) converter has much higher power density than that of traditional boost PFC converter. However, the CHB-PFC converter has multiple floating dc outputs, which leads to a common mode (CM) electromagnetic interference (EMI) issue due to the parasitic capacitance of cascaded dc/dc stages and layouts and distributed noise sources existing in the ac/dc system. Thus, a large EMI filter is necessary for the PFC system that sharply degrades the system's power density. In order to quantify the CM noise caused by the floating outputs and cascaded parasitic capacitance, a unified equivalent CM circuit model is derived in this article, which decouples the effects among the multiple CM noise sources in the CHB converter. Based on the derived circuit model, a mirror-bridge phase-shift modulation is proposed to cancel the CM noise within the CHB converter itself. A single-phase 2-kW CHB PFC prototype has been built up to verify the analysis, and 40-dB CM noise reduction compared with conventional unipolar modulation is achieved by the proposed modulation scheme.