Three-dimensional magnetic effects in permanent-magnet magnet synchronous machines

This paper presents the results of an investigation of the three-dimensional (3-D) magnetic effects in permanent-magnet synchronous machines (PMSMs). Using 3-D finite-element analysis, effects of geometry and also a high-frequency excitation on the magnetic parameters of the machine have been studied. According to our findings, high-frequency phenomena come into effect at excitation frequencies of the order of a few kilohertz, which is not uncommon when the machine is operated at super high speeds. Our results show that normalized torque productivity is a function of stack length and an increase in stack length results in an increased torque density. It is also observed that an increase in excitation frequency decreases the self inductance of the stator windings while the phase difference between the flux linkage and magnetomotive force increases. This is a significant finding, especially the shift in the phase of the air gap flux, as it has a direct impact on the accuracy of the controller that drives the PMSM under field-oriented control. Another significant observation was the reduction in the induced voltage (back electromotive force) in a search coil located in the stator slots at high frequencies. Such observations mandate the use of 3-D analysis of machine geometry to optimize performance throughout the machine's speed range.