A 500-kHz, 3.3-kW Power Factor Correction Circuit with Low-Loss Auxiliary ZVT Circuit

A new, low-loss, auxiliary zero-voltage-transition (ZVT) circuit for a boost-based power factor correction (PFC) circuit is proposed for a battery charger application in an electric vehicle. The auxiliary circuit comprises of a resonant inductor, an auxiliary mosfet, and a diode. This inductor resonates with the capacitances of the main mosfet and main diode during the turn-on transition to achieve zero-voltage switching, whereas the auxiliary mosfet itself turns off with zero-current switching. The conduction time of the auxiliary circuit is very small compared to the switching period of the main boost converter, and hence it processes only a small fraction of the output power. This allows efficient operation of the boost converter even while using Silicon mosfets at relatively high switching frequencies. A discharge mechanism comprising of a capacitor and low-frequency diode helps transfer the energy processed in the auxiliary circuit to the output. The proposed ZVT circuit has no effect on the control scheme of the main PFC, and is easy to implement with a digital processor. The operating principles, waveforms in different intervals, and the design of the auxiliary ZVT circuit are presented in detail. Some extensions of the proposed concept in terms of different discharge mechanisms and coupled-inductor implementations are also discussed. The analysis and performance of PFC with ZVT circuit and its benefits are validated through extensive simulation and experimental results from a 3.3-kW/500-kHz hardware prototype.