Electromagnetic Optimization of Switched Reluctance Motor for Torque Ripple and Vibration Mitigation

Switched reluctance motor (SRM) generates torque based on the principle of reluctance torque using a discontinuous rotating magnetic field. Double saliency of SRM causes magnetic reluctance to change with respect to rotor position. SRM is singly excited on the stator and it does not need magnetic excitation on its rotor. This feature makes SRM to be a simple, low cost, and robust configuration that makes it desirable for high speed and harsh applications. However, SRM exhibits high levels of torque ripple contributing to its acoustic response. The main contributing factor to this behavior is the non-uniform distribution of the flux and force density in SRM. To elaborate, SRM experiences a sudden rise in the flux density, in the airgap when rotor and stator poles start to overlap. This causes a sudden rise in the force density in both tangential and radial components of force at points close to the stator slot and that leads to the vibration and torque ripple. To address this problem, a novel rotor geometry with optimally designed flux barriers has been proposed in this dissertation to be used along with a conventional SRM stator. An optimization algorithm comprised of Genetic Algorithm (GA) and Finite Element Analysis (FEA) has been used to identify the best rotor geometry for maintaining average torque while minimizing torque ripple and tangential vibration of the stator. The performance of the optimized motor is then compared with a conventional SRM of the same size through experiments. The results show significant improvement in torque ripple as well as vibration for the new topology with no tangible drop in efficiency at high speeds.