A Multistage Soft Start-up Technique for SHB-FB Type DAB Converter Considering Precharge of DC Blocking Capacitors

Soft start-up in Dual-Active-Bridge (DAB) converters is a significant challenge due to the need to mitigate initial inrush currents. This challenge is even more pronounced in the Stacked Half-Bridge Full-Bridge (SHB-FB) converter incorporating an additional blocking capacitor and is a derivative of the conventional DAB converter. This paper initially assesses the start-up issues introduced by the dc blocking capacitor in the SHB-FB converter, which has received limited attention in existing literature. Then, a multistage soft start-up technique for the SHB-FB converter is proposed, considering the precharging process of the dc blocking capacitor. The technique is first validated through simulations and further experimentally verified with a Gallium Nitride (GaN)-based SHB-FB converter. The start-up challenges arising from the blocking capacitor are addressed, and experimental results show a 74% decrease in the initial inrush current compared with the hard start-up condition.