A Simple and Fast Start-Up Strategy for Dual-Active-Bridge Converters with DC Bias Suppression

High-power dual-active-bridge (DAB) converters are widely adopted in dc and hybrid ac-dc microgrids, for which fast start-up dynamics of DAB converters is a key requirement. Conventional start-up methods usually require complex operation stages, and a time-consuming parameter-tuning process, resulting in slow dynamics. In this work, we propose a new simple and optimal start-up method for DAB converters. Major contributions lie in three-folds. First, we theoretically analyze the transmission power and the peak inductor current of extended phase-shift modulation. Second, a new Lagrange multiplier method is proposed to solve the optimal phase-shift ratios of the underlying control problem, resulting in very fast control dynamics at maximum power transmission, fully respecting the system permissible current limit. Third, an effective and simple strategy by solely manipulating the gate signals in the first switching period is newly proposed to eliminate the magnetic bias. The proposed method avoids complex parameter-tuning procedures. Experimental results demonstrate the effectiveness of the proposed method. Results confirm that with the proposed solution a much faster start-up process with a controllable inductor current without dc bias is achieved, in comparison with the recently reported start-up methods.