Design and control optimization of a three-level bidirectional DC–DC converter for energy storage system

In this paper, a GaN-based bidirectional three-level dc–dc converter is designed for high power energy storage application, the voltage stress of switches at battery side is reduced to half of the input voltage without additional capacitor, PCS of battery unit is utilized to keep the stabilization of positive bus and negative bus. All the switches could achieve zero-voltage-switching by resonant. The operating mode is analyzed in detail, the resonant parameters and timing parameters is derived. In order to improve performance of proposed converter at light-load condition, the principle of ZVS failure in traditional ON/OFF control is analyzed, the relationship between operating state of converter at the end of ON stage and ZVS state entering the next ON stage is revealed, the voltage state of equal capacitor is derived. The modified ON/OFF control with optimal trigger timing and sequence is proposed to reduce switching loss according to the optimal ZVS principle. Finally, the proposed converter under modified ON/OFF control is modeled and tested in Simulink and LTspice, the experimental simulation result verifies the effectiveness of ZVS condition under bidirectional operating mode, the dynamic performance of converter under proposed control strategy is verified to be without degradation, tested efficiency is improved around 1.47% at light-load condition (10% PN) under proposed optimal control strategy.