A 6.5 kV SiC MOSFET based Inverter for Medium Voltage (2.3 kV) High-Speed Motor Drive Applications

HV SiC MOSFET based VSCs enable higher fundamental frequencies in MV drives allowing higher shaft speeds. This can potentially eliminate step-up mechanical gearboxes used in conventional Si IGBT based drives to match the motor speed with high speed compressor loads. Eliminating the gearbox helps improve the efficiency, power density, cost, and reliability of the drive. In this paper, a new 6.5 kV SiC MOSFET module and its static and dynamic characterization results have been reported. A case study of a 2.3 kV, 500 kVA high-speed industrial drive application has been performed and the benefits of the proposed 6.5 kV SiC MOSFET based system compared to a conventional 6.5 kV Si IGBT based system considering conversion efficiency, switching frequency capability and filter sizing have been presented. For hardware demonstration, a 100 kVA two-level inverter prototype has been developed using 6.5 kV, 50 A SiC MOSFET half-bridge modules for a 2.3 kV, 6000 rpm PMSM motor drive. The inverter has been tested up to the rated dc bus voltage of 4.5 kV with static load, and the experimental results have been provided, validating the converter performance. For dynamic load testing, the inverter has been tested with the high-speed motor up to 600 V dc bus and 4000 rpm (200 Hz fundamental) and the corresponding experimental results have been presented and discussed in detail.