ANALYSIS AND DESIGN OF SWITCHED RELUCTANCE MOTORS

Abstract

The research reported in this dissertation is on the analysis and design of switched reluctance motors. The focus of this dissertation is on developing several methodologies of analysis and design principles for switched reluctance motors; to study the electromagnetic characteristics and performance of SRMs and developing a miniature SRM for application as a spindle motor in hard disk drives. For the analysis and prediction of electromagnetic characteristics of the SRM, 2D FEA has been used. In addition, an analytical method, based on the equivalent magnetic circuit, has been developed to predict the magnetization characteristics of the SRMs. In predicting dynamic performance of the SRM, a dynamic model, which uses pre-calculated magnetization curves and equivalent output equation as the basic framework, has been developed. The dynamic performance of a typical four-phase 8/6 SRM, with variations of some control parameters, has been predicted using this dynamic model. The time stepping FEM technology, developed as an alternative method to evaluate dynamic performance of the SRM, has also been presented. With simultaneous computation and convergence of the field and circuit equation for the entire system, this method not only provides the changes of electromagnetic field instantaneously but also provides sufficient information for control. The comparison between the analytical method based on dynamic model and time-stepping FEM indicates that the accuracy in predicting the dynamic performance of the SRMs using dynamic model is acceptable. The influence of discretization model on the torque prediction, when using FEM, has also been studied in the thesis. The study shows that the accuracy of torque prediction depends significantly on the localized inaccuracy associated with the discretization in the entire region of the motors, especially in high-gradient fields. Some considerations in design and optimization, associated with the determination of crucial electromagnetic parameters, have been addressed. A method for a preliminary evaluation of the main dimensions has been developed. By incorporating the design method with analytical methods for predicting electromagnetic characteristics and performance, a PC-based CAD design software has been developed. This software is able to provide the initial sizing and analytical simulation for the electromagnetic behaviour and performance of the SRMs, at the preliminary design stage. The scaling in the SRM has also been investigated. The use of the scaling law is an alternative means of sizing the motor and for predicting some electromagnetic characteristics of the SRMs. Finally, two novel miniature SRMs have been successfully designed, optimized and fabricated for application as spindle motors in hard disk drives. The electromagnetic characteristics and performance of the two miniature SR motors were predicted using numerical methods and analytical methods. Also, the miniature SRM was tested for static torque and phase flux linkage. The conclusion from the study shows that a miniature SRM drive with a suitable motor structure and desirable design and control strategy can be constructed for the use in spindle of hard disk drives.