A modular front-end medium-voltage solid-state transformer

This paper discloses the development of modular front-end medium-voltage solid-state transformer (SST) to show system level design, circuit topology, and prototype test results. Each multilevel front-end module consists of two stages: (1) ac to dc boost converter with power factor correction dc and (2) isolated dc-dc LLC converter. The proposed system has been designed, simulated, and fabricated with the rating of 7.2-kV input, 400-V output, and 25-kW power capability. With the adoption of silicon carbide devices, the peak efficiency of the entire front-end converter from high-voltage ac to low-voltage dc achieves 98.2% efficiency. The individual switch is switched at 10 kHz. With complementary switching for the 3-level boost converter, the equivalent switching frequency is 20 kHz for the individual module and 200 kHz for the combined ten-module power stage. The full-voltage, full-power testing with a near ideal source shows a clean input current waveform.