Calculation of Cogging Torque in Hybrid Stepping Motors
When the windings of a hybrid stepping motor are unexcited the permanent magnet’s flux produces cogging torque. This torque has both desirable and undesirable features depending on the application that the motor is put into. This paper formulates an analytical method for predicting cogging torque using measured flux-linkage data. It assumes a linear magnetic circuit, where the magnetic stored energy and coenergy are numerically equal. Cogging torque is calculated as the differential of the magnetic coenergy with respect to rotor angular position at constant rotor excitation. By representing the flux-linkage data with analytical function, the method produced results that compare favorably with laboratory test results.