Control Strategy of a Hybrid SiC-Si Traction Inverter for Direct-Drive Multiphase PMSMs in Marine Propulsion

This article introduces a novel inverter structure tailored for direct-drive marine propulsion applications, integrating SiC-MOS and Si-IGBT devices in a hybrid bridge arm configuration. The scheme aims to enhance torque control performance by raising the switching frequency of the SiC-MOS and to minimize losses in the propulsion system by lowering the switching frequency of the Si-IGBT. Methods for torque ripple suppression and efficiency enhancement are proposed in this paper. The latter includes introducing the optimal switching frequency combination (OSFC) and optimized load distribution (OLD) methods. The OSFC method aims to determine the optimal combination of switching frequencies for Si-IGBT devices relative to the predetermined frequency of SiC-MOS devices, thereby maximizing system efficiency at the rated torque operating point. On the other hand, the OLD method adjusts the load distribution between the motor windings of SiC-MOS and Si-IGBT devices to enhance the propulsion system's efficiency, particularly under light load conditions. Moreover, experimental validation of the proposed methods is provided. Experimental results show that the proposed control strategy can reduce total drive system losses by 30% compared to an all-Si-IGBT inverter and save 35% in costs compared to an all-SiC-MOS inverter while maintaining torque control performance.