Generalized modeling and optimization of a bidirectional dual active bridge DC-DC converter including frequency variation

The paper presents a novel modeling approach of the power flow in a bidirectional dual active bridge DC-DC converter. By using basic superposition principles, the mathematical distinction of cases is avoided in the modeling process of high-frequency transformer currents for different types of modulation. The generalized model is used in an optimization of converter losses of a 3.3 kW electric vehicle battery charger with an input voltage of 400 V and a battery voltage range of 280 V to 420 V. Besides the commonly used control variables such as phase-shift and clamping intervals, also the variation of switching frequency is considered in the optimization process. The optimal modulation including frequency variation leads to an increase of converter efficiency up to 8.6% using IGBTs and 17.8% using MOSFETs in the most critical point compared to phase-shift modulation at fixed switching frequency.