MV Propulsion Drive using Solid State Transformer (SST) Technology

High frequency (50-100 kHz) power electronic converters enable attractive technology for various motor drive applications where the weight and size are largely constrained, like marine propulsion systems. SiC-based converters are the most suitable choice for high-frequency applications because of their lower switching losses than Si-IGBT based converters. However, the SiC-based MV multilevel converter solution for high-power applications is very costly in the current scenario. This paper presents a three stage (LV/DC-DC/MV) Solid State Transformer(SST) fed field oriented controlled (FOC) induction motor drive. In order to minimise cost and electrical losses, Si-IGBT and SiC devices are adopted, and a novel hybrid modulation technique is proposed for the MV stage. The MV stage of the SST-fed drive is realised with an Si-IGBT based Cascaded H-Bridge (CHB) inverter connected in series with a SiC based 2L-VSI. In the proposed control, the CHB inverter is switched at the stator frequency of the drive to supply the fundamental component of demanded voltage from the drive. As a result, it reduces switching losses to a great extent. The 2L-VSI is switched at a high frequency to supply the harmonic content, resulting in a higher effective switching frequency of the drive. The proposed technique is validated on a 300 V(LV)/1.65kV (MV), CHB based SST-fed FOC induction motor drive with different speeds and loading conditions in MATLAB Simulink environment.