Soft-Switching Solid-State Transformer (S4T) with Reduced Conduction Loss

A solid-state transformer is a three-phase ac/ac converter with a high-frequency transformer. Due to advanced features like high power density, on demand VAR support and frequency regulation, solid-state transformer is an enabling technology for the modern power distribution system. It can also find application in high-power-density motor drives. This paper proposes a new soft-switching solid-state transformer (S4T). The S4T comprises two voltage source inverter (VSI) bridges, auxiliary branches for ZVS, and transformer magnetizing inductor as reduced dc-link with 60% ripple. An active rectifier supplies power to a DC-to-DC converter, which supplies power to a Voltage source inverter. A voltage source inverter, is a power electronic device or circuitry that changes direct current (DC) to alternating current (AC). A solid-state transformer usually contains a transformer, inside the AC-to-AC converter or DC-to-DC converter, which provides electrical isolation and carries the full power. The S4T has full range zero-voltage switching (ZVS), electrolytic capacitor-less dc link, and controlled dv/dt which reduces EMI. The single-stage solid-state transformer considered in this paper is capable of bidirectional power flow and open loop power factor correction. This topology uses a minimum amount of copper and has relatively few semiconductor switches. The topology and its proposed control have been analyzed. Simulation and experimental results confirm the operation

Keywords: Solid-state transformer (SST), power electronic transformer (PET), high-frequency link (HFL), soft-switching solid-state transformer (S4T), dc transformer (DCT), current-source converter (CSC), MVDC, smart grid, distributed renewable energy resource (DER).