The torque ripple and minimization in multi-unit permanent magnet synchronous motor for electromagnetic thruster

Superpower electric propulsion requires a high-reliability high-torque and low-speed electric machine. Generally, multi-phase windings topology has been widely used to enhance the capacity and reliability of the traditional permanent magnet synchronous motor (PMSM) in the propulsion, but the usage of the multi-phase windings could bring much more complex engineering problems including controlled strategy and motor design. This paper presents a multi-unit topology low-speed high-torque PMSM, and the traditional three-phase control strategy can be simplified used in this novel motor. When all unit motors work, there is no difference of mechanical properties between multi-unit PMSM and ordinary three-phase PMSM. However, the electrical torque ripple will be produced due to asymmetry windings inductance matrix when only part of the unit motor is running. The torque ripple mechanism of multi-unit PMSM is be described in this paper, and the improved method reducing torque ripple are provided which has been verified by the finite element calculations and experiments.