Multi-objective optimization of medium voltage SiC DC-DC converter based on modular input-series-output-parallel (ISOP) architecture

This paper aims to comprehensively investigate the efficiency, power density and overall cost of input series output parallel (ISOP) medium voltage (MV) all silicon carbide (SiC) DC-DC converter in solid state transformers (SST). The medium voltage capability can be achieved by using either high voltage devices or multiple low voltage cells in series. Voltage rating of semiconductor devices, magnetic components, capacitors vary with the number of cells in series. In order to investigate the optimized number of cells, precise components' models with different voltage ratings are required, especially for the already complicated semiconductor devices. SiC MOSFET's on-resistance, output capacitance and cost models with arbitrary blocking voltages are derived based on physical device scaling law. Using these mathematical MOSFET models together with transformer and capacitor models, multi-objective optimization of an ISOP DC-DC converter system is conducted. Optimization results shows that a higher power density can be achieved by greater number of cells but single stage converter can reach higher efficiency and lower cost.