The CLLLC resonant converter naturally has symmetrical bidirectional power transmission characteristics due to its symmetrical circuit structure, but the transmission power and efficiency will be reduced when resonant network is detuned. In this paper, a mathematical model for the CLLLC resonant converter is established based on the first harmonic approximation(FHA) method. Then, a variable-frequency multi-phase-shift control strategy that can achieve bidirectional power transfer over a wide voltage range and reduce the adverse effects of detuning of the resonant network is proposed. Finally, through simulations and experiments, the proposed control strategy is proved to be able to reduce the adverse effect of detuning.

bidirectional CLLLC resonant converter,variable-frequency control,multi-phase-shift control