Phase Shift Modulation and DC-Link’s Voltage Balancing Control for a DAB DC-DC Converter

To improve the electrical energy consumption in modern transportation systems, a 1.5 kV DC bus in the future railway application has been considered by researchers and manufacturers. One of the preferred systems for this application is a high-frequency power electronics transformer to replace the existing 60 Hz power transformer. This solid-state transformer (SST) is made of multiple modules, and each module is composed of the AC/DC converter connected to a dual active bridge (DAB) DC-DC converter. A performing topology for the DAB is a three-level neutral point clamped (NPC) inverter on the left side and a two-level full bridge converter on the right side, both connected through a high-frequency isolation transformer. Due to its multilevel voltage on the primary side, its soft switching properties and the low number of components capability, the NPC based DAB converter is chosen to meet this smart transformer's requirements. This study proposes a novel control algorithm of the phase modulation and the voltage balancing perspective for future intelligent transformers.