The design of switched reluctance motors for efficient energy conversion
A new switched reluctance motor configuration is proposed, in which the windings are arranged to encourage short magnetic flux paths within the motor. Short flux path motor configurations have been modelled extensively using electromagnetic finite element analysis. It is demonstrated that short flux paths significantly reduce the MMF required to establish the B-field pattern in a motor; as a result copper losses are reduced. In addition, hysteresis and eddy current losses are decreased as the volume of iron in which iron losses are generated is reduced. Short flux paths are formed when two adjacent phase windings, configured to give neighbouring stator teeth opposite magnetic polarity, are simultaneously excited. In order to accurately model short flux path machines, a thorough electromagnetic analysis of doubly excited systems is adopted. The proposed modelling theory forms the basis for design considerations that can optimise the performance of the 4-phase and 5-phase switched reluctance motors. The electromagnetic theory of doubly excited systems is used in conjunction with a dynamic simulation program, written in Turbo Pascal, to design a 5-phase switched reluctance motor that exploits the advantages of short flux paths. Test results from the constructed prototype confirm that short flux paths significantly improve the efficiency of the switched reluctance motor. The 5-phase prototype achieves higher efficiency than all known prior art switched reluctance motors and industrial induction machines constructed in the same frame size. At the [1300rpm, 20Nrn] operating point the efficiency of the 5-phase drive was measured to be 87%. The corresponding motor efficiency was in excess of 89.5%.