A Boost-LC Resonance Multimode DC-DC Converter for EV Charger Application

This article proposes a Boost-LC resonance multimode dc-dc converter for EV charger application. The converter adds an additional leg to the conventional full-bridge (FB) LLC resonant converter. By adopting the hybrid modulation method of pulsewidth modulation (PWM) and pulse frequency modulation (PFM), the proposed converter can have three operating modes within a narrow switching frequency range. In high-voltage-gain (HG) mode, the boost energy storage stage replaces the LLC resonant energy storage stage of the conventional FB LLC resonant converter, which effectively improves the voltage gain. Thus, the magnetizing inductor of the proposed converter can be designed large, the magnetizing current and the circulating current are small. In addition, the voltage stress of the resonant capacitor of the proposed converter is small, which is conducive to the realization of high power density. In medium-voltage-gain (MG) and low-voltage-gain (LG) modes, the converter works as conventional FB and half-bridge (HB) LLC resonant converters, respectively, but has a smaller magnetizing current. In this article, the operation principle, the voltage gain formula, the design method, and the topologies comparison are introduced in detail. Finally, an experimental prototype with 200 V input voltage, 75-300 V output voltage, and 0-5 A output current was built. The experimental results verify the correctness of the theoretical analysis.