I. Introduction
In order to reduce fossil fuel combustion and carbon dioxide emissions, electrical machines are applied in various industries [1], [2]. Among them, interior permanent magnet (IPM) synchronous machines have been widely used due to their advantages of high torque density, high efficiency, and wide speed range [3]. Different from surface permanent magnet (PM) machines, IPM machines use embedded PM to generate rotor flux, with high magnetic saturation in regions such as stator tooth crowns [4] and rotor bridges [5], which needs to be analyzed combining the nonlinear characteristics of iron core [6].