Model Predictive Control for Dual Active Bridge Converters in Light Load Operation

The Dual Active Bridge (DAB) converters have been widely utilized in isolated DC-DC applications such as power modules for charging piles and solid-state transformers. However, their efficiency tends to decrease significantly when the output power is substantially lower than their nominal rating. To address this problem, this paper presents a Model Predictive Control (MPC) strategy that integrates variable switching frequency modulation and single-phase-shift modulation. To begin with, this paper derives the relationships among the output power and two control variables, i.e. the switching frequency and the phase shift. A hybrid numerical and geometric method is applied to obtain the optimal references for the control variables by minimizing the current stress of the circuit. The resulting conditions are integrated into the cost function of the MPC algorithm to approach the optimal working point for high efficiency under any given output power level, especially light load. Both control variables are discretized to create a finite control set, which facilitates the implementation of MPC on digital processors. The simulation results demonstrate the effectiveness of the proposed method in optimizing current stress and achieving ZVS under light-load conditions.