Modulation of 2/3-Level Dual-Active-Bridge DC-DC Converters for Soft-Switching and Minimum Current Stress

This paper proposes an optimal modulation scheme for two-three (2/3)-level dual-active-bridge (DAB) DC-DC converters to guarantee zero-voltage-switching (ZVS) operation and minimize the current stress. Based on the unified ZVS principle, six operating modes are defined and constraints of each ZVS mode are then obtained. According to the operating modes, the power transmission model and current stress under all voltage conversion ratios are derived for optimization. The analytical solutions for minimum current stresses are obtained by using the Lagrange multiplier method with Karush-Kuhn-Tucker conditions. With the proposed modulation scheme, both the conduction and switching losses can be reduced, and thus, the entire efficiency can be improved. Finally, simulation results verify the theoretical analysis and the performance of the optimal modulation scheme.