Rotor induced harmonic voltages caused by supply voltage distortion, the interaction and its influence on the overall energy efficiency of Line Start Permanent Magnet Machines

The demand for ever increasingly efficient electromechanical energy conversion has resulted in the commercialization of medium power Line Start Permanent Magnet Motors. Similar to the standard Direct On line induction machines are these machines susceptible to grid voltage distortion. As LSPMM are to become a mature technology, the influence of voltage distortion on their efficiency should be addressed. The grid voltage distortion is composed of multiple harmonic components and in this paper it will be elucidated that, due to the synchronous operation, a specific interaction of rotor harmonic currents induced by different stator harmonic orders can be noticed. Although straight forward adaptation of harmonic loss mechanisms for standard squirrel cage induction motors to the LSPMM seems logic, this research will reveal that harmonic loss models of induction machines are unsuitable to give accurate or even reasonable estimations of the influence supply voltage distortion on the energy efficiency of LSPMM.