Design and performance analysis of a novel flux-concentrating fault tolerant permanent magnet vernier machine for rim driven thruster

Permanent magnet vernier machines (PMVMs) have attracted a great deal of interest in recent years. This type of motor offers benefits such as high torque density and reliable operation. The rotor of a spoke-array fault-tolerant PMVM (SAFT-PMVM) has a magnetic flux focusing effect. However, due to its unique topology and application areas, the air gap length is usually larger than that of traditional motors with the same power. When the air gap length increases, the magnetic flux focusing effect is significantly weakened, resulting in a large torque reduction in SAFT-PMVMs, even lower than that of surface-mounted fault-tolerant PMVMs (SMFT-PMVMs). To address the above issue, a novel flux-concentrating fault-tolerant PMVM (FCFT-PMVM) for rim-driven thrusters is proposed by employing permanent magnets with radial and tangential hybrid excitation with the aim of improving the torque density. The mechanism of improving motor torque is analyzed using the equivalent magnetic circuit (EMC) method, and the performances of SMFT-PMVM, SAFT-PMVM, and the proposed FCFT-PMVM are analyzed through the finite element method (FEM). Results reflect that the proposed motor has several advantages, including high output torque, low torque ripple, and good fault tolerance. Finally, the experiments are conducted on surface-mounted PMVM to verify the feasibility of the design.