New Secondary-Side Control Scheme for DAB Converter with Both Side Isolated

The application of solid-state transformer (SST)based converters has been extensively studied to achieve high efficiency and power density in railway power systems. However, in SST-based designs for railway systems, achieving high insulation voltage equivalent to the system input voltage is necessary for the transformer. To address this issue, fully isolated control methods have been proposed. Nevertheless, such methods have the drawback of unreliable secondary-side output voltage regulation under varying input voltage conditions. In this paper, a new primary-side control (PSC) method is proposed to achieve stable output voltage regulation in DAB converters. The proposed method adjusts the switching frequency by measuring the input voltage. Additionally, the switching timing and frequency on the primary side can be detected through the additional inductor on the secondary side. As a result, the proposed method can effectively regulate the output voltage. To verify the effectiveness of the proposed control method, a 400 V input, $400 \mathrm{V} / 1 \text{kW}$ output experimental prototype was developed and tested.