I. Introduction
With the characteristic of high torque at low speed, Permanent magnet synchronous motor (PMSM) has been more and more widely used in the automotive electronic control field, such as the electric power steering system (EPS) and steering by wire. But the torque ripple directly affects the low-speed stability of PMSM, control accuracy, and the comfort of driver's operation. There are many factors that cause torque ripple, such as cogging torque, flux harmonics, sampling error.