Asymmetric Parameters Design for Bidirectional Resonant CLLC Battery Charger

Abstract

The CLLC bidirectional resonant converter has significant potential in chargers and DC microgrids, due to its bidirectional power transfer capability. To ensure characteristics consistency of bidirectional operation, traditional symmetrically designed resonant tanks are usually adopted. Traditional symmetrical tanks are effective for the application without voltage regulation such as CLLC DC transformers. However, for bidirectional battery chargers, the bidirectional operating characteristics are not the same, because of asymmetric voltage and load of two sides. Therefore, the traditional symmetrical resonant tank design would cause undesirable large frequency range to provide wide voltage gain range, especially for Wide Battery Voltage Range (WBVR) operation. To address conventional symmetric design issues, detailed asymmetric parameters methodology(APM) is proposed in this paper. Reasonable ranges of each normalized parameter are obtained by considering the constraints of APM. Based on these ranges, the statistical Design of Experiment (DoE), instead of using FHA model, is adopted to obtain more precise frequency responses of CLLC converter towards variations of parameters in wide switching frequency range. The APM enables more similar switching frequency ranges in Charge Mode (CM) and Discharge Mode (DM), thereby reducing the overall frequency range of WBVR operation. This could lower switching loss caused by excessive high-frequency charging under Low Battery Voltage (LBV) in CM, and relieve the extra conduction loss and current stress of power components as well when batteries is discharged at LBV in DM. Finally, the proposed method is proved by experiments.