Design and Comprehensive Analysis of Magnetic-Geared Permanent Magnet Synchronous Motor for Single-Propeller Underwater Propulsion

Abstract

This paper presents a magnetic-geared permanent magnet synchronous motor (MG-PMSM), which is an integrated structure composed of a permanent magnet synchronous motor (PMSM) and a magnetic gear (MG) for autonomous underwater vehicles (AUVs). The MG-PMSM features a dual rotor structure: a high-speed permanent magnet rotor (PMR) and a low-speed pole piece rotor (PPR). To meet the required load conditions of the single propeller of the AUV, the PPR, directly connected to the output shaft, operates under load conditions, while the PMR operates under no-load conditions. The aim of this study is to use finite element analysis (FEA) to investigate the overall electromagnetic performance of the proposed MG-PMSM with different gear ratios and slot/pole combinations. Subsequently, a structural analysis of the PPR and its support structure is conducted using FEA to validate the strength of the PPR structure. Furthermore, thermal analysis is performed using computational fluid dynamics. The results of the structural and thermal analyses demonstrate sufficient structural strength and thermal stability, respectively. Finally, the electromagnetic performances of the proposed MG-PMSM are compared with the PMSM and MG configuration. The results show that, although the MG-PMSM exhibits nearly identical efficiency, it achieves an 11.4% increase in volumetric torque density per unit active volume compared to the PMSM and MG configuration. Moreover, when accounting for the inactive volume of the integrated underwater propulsion system, the volumetric torque density is expected to increase further.