Analysis of air gap length by radial electromagnetic force in interior permanent magnet synchronous motor considering flux-weakening control

The contradiction between the demand for high speed and high power density of electric vehicle drive motor and the extreme driving experience of low vibration noise is becoming increasingly significant. It is a fact that the investigation on vibratory noise of permanent magnet synchronous motor (PMSM) under high-speed conditions has attracted increasing attention. This paper investigates the electromagnetic characteristics of interior permanent magnet synchronous motor (IPMSM) considering flux-weakening control. First, this paper deconstructed the mathematical expression of PMSM radial force; moreover, the principle of the leading angle flux-weakening (FW) control is analyzed. Second, the co-simulation model is built through by field-circuit coupling method. Then, IPMSMs with different air-gap lengths are simulated under maximum torque per ampere (MTPA) control and flux-weakening control, respectively. At last, the simulated results of air-gap flux density and radial force are discussed. The results of the experiment indicate that appropriate increase in the air-gap length of PMSM is conducive to the weakening of the radial force and can reduce the vibratory noise of PMSM. Through the analysis of air-gap magnetic field under flux-weakening control, it is found that the radial force of PMSM is weakened when the flux-weakening control at high speed. It is further verified that the basic principle of flux-weakening control is to weaken the air-gap magnetic field by increasing the direct axial current reversely, so as to improve the speed.