Nonlinear theory of the switched reluctance motor for rapid computer-aided design

The nonlinear magnetisation characteristics are modelled analytically by piecewise first- or second-order functions of flux linkage against rotor position, with current as an undetermined parameter. The model is suitable for CAD and performance analysis, particularly at the stage of `sizing´, or initial estimation, where accuracy can be traded for speed of computation. The model includes all the significant electromagnetic and dynamic characteristics of the SR motor. Its accuracy can be enhanced by means of correction factors derived from only two or three points on magnetisation curves that have been accurately measured or calculated by finite elements, permitting economy in the use of data that is expensive to generate. A piecewise analytical formula for instantaneous torque is also included, permitting the rapid calculation of mathematically smooth torque waveforms. Because the magnetisation curves do not need to be precalculated, stored or curve-fitted, the algorithms are extremely fast. The paper also presents a new method for calculating the unaligned magnetisation curve, based on dual-energy principles. Results are compared with test data for a range of motors