Bidirectional charger control strategy for low-voltage charging based on DAB circuit

The dual active bridge bidirectional battery charger (DAB-BBC) is a critical device for railway trains to achieve emergency traction functionality. Single-Phase Shift (SPS) control is widely employed in DAB-BBC circuits due to its advantages such as control simplicity and the capability for online switching. To address the challenge associated with excessive output capacitor ripple current, which hinders low-voltage charging in SPS-controlled DAB-BBC systems under low battery voltage conditions, this paper proposes a Primary Side Phase Shift (PSPS) control strategy. The study provides a thorough analysis of the operating modes, power transfer model, soft-switching characteristics, output capacitor ripple current characteristics, and charging voltage range of the bidirectional charger under PSPS control. Simulation and experimental results demonstrate that when the battery voltage is below 70 V, the proposed PSPS control strategy reduces the output capacitor ripple current by over 50% compared to conventional SPS control. This control strategy enables low-voltage charging of batteries.