Parasitic Component Inclusive Optimum Phase-Frequency Contour Enabled Synchronous Rectification of Asymmetric CLLC Resonant Converter

With an objective to reduce the switching losses in a bidirectional resonant CLLC DC/DC converter for electric vehicle (EV) charging applications, this paper presents an elaborate frequency dependent general harmonic approximation (GHA) based secondary side turnoff current minimization technique by investigating the optimum operating point to achieve synchronous rectification (SR). Formulation of an accurate all-inclusive gain model is presented, specifically focusing on effect of parasitic components on the resultant gain-frequency trend, backed with thorough experimental validation. Further, meticulous modeling of the GHA based state equations is presented to obtain a contour of feasible operational frequencies and corresponding phase shifts to ascertain accurate SR operation with a multi-dimensional optimization technique to ensure reduced switching losses. In addition to that, to precisely characterize the resonant tank equivalent circuit, stressing on its effect on SR phase calculation, a detailed 3D finite element analysis (FEA) based R-L-C modelling of the employed high frequency planar transformer (HFPT) is explained. To validate and benchmark the performance of the proposed gain model while ensuring accurate SR operation, a 1 kW all-GaN based CLLC experimental prototype is developed for a resonant frequency of 500 kHz, with a power density of 106 W/inch
³
. Experimental waveforms at corner conditions are presented for a wide-gain bidirectional operation, portraying a peak converter efficiency of 98.49%.