Mutual-inductance modelling in line-start permanent-magnet synchronous machines based on winding-function theory

In this paper an analytic method to study space-harmonic effects and to map the influences of geometric design parameters on the line-start permanent-magnet synchronous machine (LSPMSM) dynamic performance (start-up and other transients) is presented, based on Winding Function Theory (WFT). The mutual inductances between a rotor, containing barriers and iron bridges near the magnets, and a stator with concentric windings are computed. As the iron bridges near the magnets are in saturation due to the high magnetic field of the magnets, the assumption is made to represent the rotor in different parts. Each part has a high permeability, and is separated by a layer of low permeable material, i.e. the magnets, the saturated bridges and the barriers. The magnetic coupling is described, and the different computation methods to obtain mutual inductance values are given. Using finite element methods (FEM) the WFT-resulting inductances are verified.