Controller and EMI filter design for modular front-end solid-state transformer

This paper discusses the details of the control scheme and EMI filter design for a modular front-end solid-state transformer (SST). The multi-cell configuration is achieved by connecting the active-front-end (AFE) cells in series, with the voltage from the MV evenly distributed among the cells. The isolated outputs of the dc-dc converters are tied in parallel. The EMI filter is designed to reduce line impedance and switching noise. Simulations showed the EMI filter reduced noise below FCC Class A standards. The SST controller consists of a voltage controller, current controller, and a phase lock loop (PLL) with an ideal duty feedforward. The implementation of these subsystems is explained and its integration in the system is shown. The results show that at low voltage level, the input current waveform is nearly sinusoidal.