Starting Performance Improvement of Line Start PMSM by Reduction of Space Harmonics

Line start permanent magnet synchronous motors possess many attractive features including high efficiency, low loss, high power factor, small volume and light weight. Also they need no inverter for starting which is economical for many single speed applications such as most fans, pumps and compressors. Therefore LSPMS motors have been considered as an alternative for induction motors, but the starting performance of LSPMS motors have been a challenging issue concerned by many researchers so far . Compared to Induction motors, because of braking torque due to permanent magnets, the winding space harmonics and their negative impacts on LSPMS motors torque characteristics should be considered more serious. In this paper, first the mmf distribution of stator winding in the air gap is studied based on Fourier analysis. Then by using an optimization process, a new stator winding has been developed, which has a lower harmonic content in its mmf than the conventional winding. Finally the method is applied to an existing LSPMS motor and its performance is obtained by a finite element analysis.