Comparison of GaN based CLLC converters for EV chargers operating at different switching frequency ranges

In this paper two 3.6 kW GaN based CLLC converters for EV chargers are compared. One CLLC converter is designed with a high resonant frequency (HF) and the other with a lower (LF). With the help of the fundamental harmonic approximation (FHA) the CLLC converters are designed. To cover the wide voltage range of the battery, the voltage gain curves of the CLLC converters are considered to operate above and below the resonant frequency. The converter is analyzed using the FHA, simulations and in measurements. Both converters are built up and the gain curves and switching behavior are investigated. Especially the zero voltage switching is considered for both LF and HF CLLC converters. Finally a CLLC converter with zero voltage switching over the entire operating frequency range is found. However the limits of the FHA design method for CLLC converters are elaborated.