Control and Efficiency Optimization of Dual-Active-Bridge DC/DC Converter

Bidirectional isolated DC-DC converters such as Dual Active Bridge (DAB) converters are key components for the solid-state transformer (SST) applications. However, the efficiency of DAB converter with the traditional control, namely Single-Phase-Shift (SPS), is very low due to high circulating current. In this paper, the power flow characteristics of DAB converter is analyzed and then the expressions for the backflow power are obtained. In this paper, extended-phase-shift (EPS) control is adopted to minimize the backflow power. A comprehensive comparison of EPS and SPS is conducted in terms of the transmission power, backflow power and peak current. Meanwhile, the design of the closed-loop control with EPS is presented. Finally, in order to confirm the correctness of proposed control strategy, a 20 kHz 1kW DAB prototype controlled by TMS320F28335 DSP was built and main test results were presented.