A Single-Stage Three-Phase Isolated AC-DC Converter for Medium Voltage Solid State Transformer Applications

A three-phase, single-stage, isolated AC-DC converter that can achieve low total harmonic distortion (THD), aimed at Medium Voltage (MV) Solid State Transformer (SST) applications is introduced in this paper. Combining three-phase power-factor correction (PFC), and discontinuous-current mode (DCM) boost rectifiers with a highly efficient resonant converter, the proposed single-stage SST features low cost, simple control, and high efficiency. The whole converter deploys only one MV power transformer to reduce the cost and efforts of the isolation design. The evaluation is performed on a 12 kW prototype operating at 3.4 kV DC-link voltage. The measured input current THD is less than 4% without any active control.