Analysis of Position Information via Asymmetric Inductance of Permanent Magnet Linear Synchronous Motors

The end effect in permanent magnet linear synchronous motors (PMLSMs) causes force ripple and asymmetrical electromagnetic parameters. The end effect is generally regarded as detrimental, with substantial research efforts directed toward mitigating the end effects. However, the end effects are directly related to the motor position and may contain information that can serve as a source of position signals for sensorless control methods. Therefore, this paper investigates the end effects and finds that the end effects lead to asymmetry in the three-phase inductances. Furthermore, this paper analyzes the asymmetric inductance characteristics of PMLSMs and derives the model of asymmetric inductance in the rotating coordinate system. Finally, this paper the finite element analysis is used to simulate PMLSMs with and without end teeth. Theoretical derivation and simulation results demonstrate that the asymmetry of the three phase inductances lead to the position-dependent second harmonic in the d-axis and q-axis inductances. The position information contained in the inductances can potentially serve as a source of position signals for sensorless control methods.