Dual-Mode Control Scheme to Improve Light Load Efficiency for Dual Active Bridge DC-DC Converters Using Single-Phase-Shift Control

In vehicle-to-grid (V2G) applications, dual active bridge (DAB) converters are commonly used as the power interface because they offer high efficiency, galvanic isolation, and bidirectional power flow. For the DAB control strategy, phase-shift control is the mainstream, especially the single-phase-shift (SPS) method because of its ease of implementation. However, due to the phase shift, a DAB converter operated under this control method has relatively high backflow power, resulting in poor efficiency. The SPS control method has the drawback of high backflow power, especially at light loads. Thus, this paper proposes a new dual-mode control scheme to improve the light load efficiency of DAB converters by taking advantage of the pulse-width modulation (PWM) strategy in combination with the conventional SPS strategy for DAB converters based on load conditions. In other words, when the DAB converter operates under light load conditions, the PWM control strategy is used to avoid considerable backflow power. A prototype DAB converter with a power rating of 1 kW under a switching frequency of 100 kHz interfacing a DC bus (400 V) and a battery pack (50 V) is designed and implemented to verify the feasibility of this control strategy. A detailed analysis of the working principle and design parameters of the proposed converter is provided in this paper. Experimental results show that the highest efficiency of the proposed converter at light loads (10–200 W) was 96.2% for the forward power conversion and 97.3% for the backward power conversion.