A Method for Detecting and Mitigating Steady-State DC Bias Current in Dual Active Bridge Converter

Dual Active Bridge (DAB) converters are widely used in various power transfer applications due to its several advantages like high power density, simple control methodologies, galvanic isolation, soft switching and bidirectional power flow. However, the high-frequency transformer of the converter suffers from magnetic flux bias due to volt-sec imbalance both in steady state and transient state. The steady-state dc bias current (DCBC) in the DAB converter is generally caused by asymmetric switching of the power switches. So, to minimize the DCBC that appeared during steady state operation, this paper proposes a method to detect the dc offset current and actively minimize it by controlling the duty ratio of the power switches of the H-Bridges individually. In this paper, a DCBC detection algorithm is proposed which detects the dc offset current from the peak values of the leakage inductor current. The conditions for achieving zero dc bias current are derived from the small signal model. Two-stage control has been employed in order to minimize the DCBC and to restore the output power delivery which got hampered during DCBC minimization. Lastly, the proposed technique will be verified by the results of the simulation performed in MATLAB R2024a.