Effect of voltage subharmonics and interharmonics on currents of line start permanent magnet synchronous motor

This study deals with currents of a line start permanent magnet synchronous motor (LSPMSM), supplied with voltage containing subharmonics and interharmonics – components of the frequency less than the fundamental frequency or not being equal to its integer multiple, respectively. The results of experimental investigation are presented for a factory-made four-pole LSPMSM of the rated power 3 kW. Voltage interharmonics result in the flow of current components of various frequencies and comparatively small values. Their presence could lead to resonance phenomena, but is not expected to cause the motor overheating. Contrastingly, voltages subharmonics cause the flow of significant current subharmonics, which may considerably increase power losses, and consequently – the thermal loads of the LSPMS.