A Four‐Degrees‐of‐Freedom Modulation Strategy for Series Resonant DAB DC‐AC Application

ABSTRACT In this article, a bidirectional DC‐AC modulation strategy for series resonant dual active bridge converter (SR‐DAB) is proposed. This modulation strategy combines phase shift (PS) and variable frequency (VF), which utilize four control variables, namely, three PS ratios and switching frequency. Three of four control variables are used for every operating scenario. Modulation methods under both buck and boost modes are considered and designed to attain a wide voltage gain range. Situations when modulation variables reach near transition limits are also given attention by introducing the notion of transition mode to realize smooth transition. The modulation strategy is optimized and designed by considering the operating constraints and the power losses in all aspects. Comparison of this optimization strategy with other strategies is carried out to prove the advantages of the proposed strategy. Finally, a 500‐W prototype is designed and built, which can operate under the condition of input DC voltage 10–50 V and output AC voltage 220 V rms , 50 Hz, and the measured peak efficiency reaches 96.2%.