Study, Quantification, and Correction of Steady State DC Current in the Transformer of Nonresonant Dual Active Bridge Converters

The efficiency of dual active bridge (DAB) converters can be greatly improved by using gallium nitride (GaN) semiconductors and high-frequency power transformers. However, the variation in the internal resistance of these devices, and possible time mismatches create an unwanted stationary dc current in the power converter transformer. In this article, a mathematical quantification of the steady-state dc current in nonresonant DAB converters is introduced and the formulation isvalidated through both LTspice simulations and experimental results obtained on a prototype employing GaN enhancement-mode high electron mobility transistor (e-HEMT) devices. Moreover, a closed-loop voltage compensation control strategy is proposed to effectively mitigate this parasitic dc current. The analysis comprehensively investigates the influence of semiconductor resistance variations and temporal mismatches, demonstrating that the correction of the dc component significantly enhances system stability and boosts overall efficiency.