Scaling and dimensioning of switched reluctance machines

A scaling law applying to a geometrically analogous series of switched reluctance machines (SRM), based on two‐dimensional non‐linear field analysis is presented in the paper. It highlights the fact that both linear and saturated permeances per unit axial length at different rotor positions are invariant under scaling. Based on a normalized static energy conversion loop in the electric/magnetic loading plane a quality factor is defined which serves to calculate the average specific torque. A simple analytic expression for predicting the quality factor of a SRM is derived which depends only on the linear permeances at two extreme rotor positions and the electric and magnetic loadings at the top point of the static energy conversion loop. This simplifies greatly the prediction of specific torque at an early design stage. Finally, the effects of air‐gap dimension ratios, electric loading, magnetic gear ratio and leakage flux on the quality factor and the specific torque in designing SRM having different magnetic gear ratios are discussed.