Natural Soft-Switching Extended Phase-Shift Control of Dual Active Bridge for High-Efficiency Battery Charging and Discharging

Abstract

The dual active bridge (DAB) converter, owing to its capability for electrical isolation and bidirectional energy flow, is well-suited for battery charging and discharging applications. Existing battery charging strategies typically exhibit low voltage and high current during the initial charging phase followed by high voltage and low current during the later phase. Under these operating conditions, achieving zero voltage switching (ZVS) for all DAB switching devices is challenging, which limits the efficiency and overall performance. To address these limitations, this paper adopts a Neutral-Point-Clamped H-bridge (NPC-H) DAB topology to mitigate voltage stress on the input-side switches. For both charging and discharging scenarios, a direct current control method is proposed using the output current as the primary control variable. Additionally, a Natural Soft-switching Extended-Phase-Shift (NSEPS) strategy is introduced to optimise current stress while leveraging natural soft-switching, ensuring efficiency optimisation across the entire charging cycle. Simulation and experimental results validate the theoretical analysis demonstrating a peak efficiency of 97.52%.