Dead-Time-Based Soft-Startup Strategy Enabling ZVS for DAB Converters in Railway Station Fast-Charging System

Abstract

In railway-station fast-charging systems, Dual Active Bridge (DAB) converters are widely employed as DC/DC conversion stages and are typically operated in a multi-module configuration. During the initial start-up, it is essential to suppress excessive inrush current through an effective soft-start strategy. A soft-start method that adjusts dead time has been introduced to suppress inrush current while reducing the required number of PWM channels and simplifying the overall control structure. However, despite these advantages, this method inherently fails to achieve zero-voltage switching (ZVS) on the primary-side switches. To address this limitation, this paper proposes a novel dead-time-based soft-start strategy that enables ZVS operation while simultaneously mitigating inrush current. The proposed method prevents hard switching of the power devices from the initial stage of converter operation, thereby reducing device stress and switching losses. As a result, the overall reliability and lifetime of the fast-charging system are significantly improved. The effectiveness of the proposed strategy is validated through detailed simulations conducted on a 10 kW charging module operating with an input voltage of 800 V and an output voltage of 500 V.