An Improved Methodology to Minimize Transient 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. This paper presents the effects of the transient dc bias current on a DAB converter with an approach to minimize it. The transient dc bias appears in the DAB converter due to sudden change of phase shift duty ratio between two H-bridge pulses, load change, reversal of direction of power flow etc. This paper mainly analyses the common types of transient DC bias that appear in DAB converters. To minimize the transient dc bias, a control logic is implemented which will change the phase shift duty ratio in several steps and will also keep the peak leakage inductor current within specified limit. The change in phase shift duty ratio will take place during the zero crossings of the leakage inductor current. The zero crossing detection of the leakage inductor current comprises the Fourth Order Generalized Integrator (FOGI) based filter and a zero crossing detection algorithm. The FOGI is used to extract the fundamental component from the leakage inductor current response and the zero crossing detection algorithm analyzes the zero crossing of the fundamental component. The various results of the causes of transient dc bias current and results of the proposed approach to minimize the transient dc bias current are verified by simulations performed in MATLAB R2024 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$a$</tex>.