I. Introduction
The permanent magnet synchronous motor has a simple structure, small size, light weight, low loss, and high efficiency. Compared with DC motors, it does not have mechanical commutators or brushes; Compared with asynchronous motors, it does not require reactive excitation current, resulting in high power factor, low stator current and resistance losses, measurable rotor parameters, large stator rotor air gap, and good control performance. In recent years, with the continuous improvement and improvement of the performance of permanent magnet materials, as well as the gradual maturity of research and development experience in permanent magnet motors, permanent magnet motors have been increasingly widely used in national defense, industrial and agricultural production, and daily life, and are developing towards high-power (high speed, high torque), high functionality, and miniaturization [1–3].