Direct Phase-Shift-Angle Optimization Strategy for DAB Converters’ Efficiency Enhancement Based on Fundamental Extended Phase-Shift Modulation

Abstract

The dual-active-bridge (DAB) converter is widely employed in dc conversion owing to its symmetrical structure, ease of operation, and high efficiency. However, its efficiency decreases under light-load conditions, especially when the voltages are severely mismatched with the transformer. This article proposes a fundamental extended phase-shift (FEPS) modulation method based on the frequency-domain model to improve light-load efficiency. This strategy can not only improve the converter efficiency but also resolve the difficulty of determining the peak current in the time-domain model inherent to EPS modulation. Moreover, based on the optimization results and exploiting monotonicity, a direct phase-shift-angle optimization (DPO) strategy is further proposed, which can reduce the computation of the DAB system. Experiments are conducted on a small experimental platform and compared with several existing optimization methods. The experimental results of efficiency tests verify the effectiveness of the FEPS modulation and DPO method proposed in this article.