Hybrid LLC Resonant Converter With Partial-Power Auxiliary Unit for Improved Performance

Abstract

DC-DC converters used in on-board chargers (OBC) of electric vehicles need to meet the requirements of high efficiency, wide output range, and electrical isolation. In this article, a partial-power processing topology with a wide output range is proposed to overcome the drawbacks of traditional single-stage and two-stage LLC converters. The LLC resonant converter operates near the resonant frequency to maintain high efficiency. While only the partial power is processed by the Buck converter to offer the wide-range output voltage capability. The triangular current mode (TCM) operation is implemented in the Buck converter to minimize the efficiency sacrifice. In addition, to reduce the adverse effect of the second harmonic voltage ripple (SHVR) generated by the AC port on the LLC resonant converter in OBC. A ripple compensation method is proposed to eliminate the SHVR of the LLC resonance converter. Through the dual predictive control for the Buck converter, the SHVR of the LLC resonant converter is offset by the Buck converter. A 2 kW rated experimental prototype is designed to convert 400 V wide input to 200-500 V output. The prototype demonstrates more than 96% efficiency from 30% load to full load at 60-120 V input and a 98.2% peak efficiency.