Optimal Design of Turn-Off Switching Loss of Full-Bridge CLLC Converter

The turn-off loss of the switches is the main loss of the full-bridge
CLLC
converter under high-frequency conditions, and it is a variable closely related to the resonance parameters of the resonant tank and the voltage gain. First, the gain characteristics of the full-bridge
CLLC
converter are analyzed based on the first harmonic approximation (FHA). Then, the precise functional relationships of the switches’ turn-off current and turn-off loss are derived by time domain analysis (TDA). On this basis, the constraint space of resonance parameters is reduced based on the monotonicity constraints of the gain curve, soft switch realization conditions, overall efficiency constraints, and turn-off loss characteristics constraints, and the particle swarm optimization (PSO) algorithm is used to solve the resonant parameter under the turn-off loss optimization. Finally, a simulation model was built through optimized parameters, and prototype experiments were carried out. Meanwhile, compared with the traditional loss optimization method, it is proven that the proposed method can make the output voltage closer to the design value and reduce the turn-off current and turn-off loss under the premise of ensuring soft switching.