Optimized modulation scheme for isolated bidirectional dual active bridge DC-DC converter to minimize current stress in the whole load range

This paper proposes an optimized modulation scheme for the dual active bridge (DAB) converter, which leads to the minimum current stress in the whole load range. The effective switching modes are distinguished by three control parameters: two inner phase-shift ratios and the outer phase-shift ratio. This paper derives the expressions of the transmission power and the current stress for each effective switching mode, which are taking three control parameters as variables. The Karush-Kuhn-Tucker (KKT) conditions are then applied to derive local optimal control parameters for minimizing the current stress and the closed-form solutions for power ranges. By combining the effective switching mode operations, the global minimum current stress is confirmed, besides the global optimal control parameters with the required transmission power and voltage conversion ratio in the whole load range. Finally, an experimental prototype is implemented and the experimental results validate that the current stress optimization and efficiency improvement are realized by using the proposed modulation scheme.