Analytical prediction of torque and inductance characteristics of identically slotted doubly-salient reluctance motors

In the paper, the numerically computed variation of normalised permeance and force with apparent tooth flux density (tooth pitch flux/tooth area) is given for identically slotted doubly-salient structures. In the computations, a commercial steel B-H characteristics is used. The data cover the range of structural variables encountered in most commercial stepping motors. Flux densities reaching heavy saturation (up to 2 T) are considered. The variables in presenting the data are chosen to be dimensionless or size independent to facilitate application to a wide range of practical motor structures. The effect of structural variables on torque under different levels of saturation is investigated from the curves and the conclusions are presented. An analytical method of static torque and inductance curve prediction for identically slotted doubly salient devices based on numerically calculated force and permeance data is also developed and applied to heavily saturated stepping motors. The results are found to be in very good agreement with the measurements. The method thus provides designers with an accurate and versatile tool.