An Optimal Modulation Strategy to Minimize Backflow Power with Full Soft-Switching Capability for Dual Active Bridge Converters under Light-Load Conditions

Backflow power causes power circulation in the dual active bridge (DAB) converters, leading to additional copper loss and reduced efficiency. However, achieving minimal backflow power conflicts with full soft-switching capability. When the backflow power drops to zero, some switches lose their soft-switching capability, leading to switching losses and reduced efficiency. Additionally, backflow power can be effectively reduced by lowering the inductor current required for soft switching. However, this will extend the discharge time of the junction capacitor and shorten the freewheeling period during the dead time, making it challenging to select the appropriate dead time and potentially leading to soft switching failure. To address these issues, this paper systematically examines the relationship between backflow power and the current required for soft switching. It further analyzes the transient process during the dead time, determining the minimum inductor current and the corresponding dead time required for each switch to achieve zero-voltage switching (ZVS). Moreover, an optimal modulation strategy is proposed based on waveform analysis considering dead time, minimizing backflow power while enabling full soft-switching, thereby improving system efficiency. Experimental results confirm the effectiveness and superiority of the proposed method.