Analysis and Design of Three Phase Y-Y LLC Converters for Battery Chargers Based on Time-Domain Model

The three-phase Y-Y LLC converter is considered as a promising candidate for the high-power battery charger. However, conventional first harmonic approximation (FHA) method has poor accuracy when designing three-phase LLC battery chargers with a wide voltage and power range. This paper utilizes time-domain analysis (TDA) to model the three-phase Y-Y LLC converter. The operation modes and boundary distributions are presented completely. Then, a convenient worst-case based design method is proposed using the TDA method, which guarantees the soft-switching in entire working range and minimizes the circulating current. The validity of TDA model and its design method are verified through simulation and comparison. The errors are less than 0.7% in wide voltage range, much lower than FHA. As the indicator of efficiency, the root-mean-square (RMS) value of resonant current decreases up to 21.8% compared to FHA model.