The Reactive Torque of a PMBL Motor with Magnets in Closed Rotor Slots

Abstract

A mathematical model of a PMBL motor with permanent magnets embedded in the rotor body is considered. The model is based on decomposing the active region into homogeneous cylindrical sections with de-energized magnetic sheets at their boundaries. The techniques applied in the method for separating the Fourier variables and magnetization of magnetically hard and magnetically soft media are used as model numerical analysis tools. It is shown, based on calculated and experimental data, that in a PMBL motor with magnets located in closed rotor slots, a discrete bevel of magnets per stator tooth pitch does not make it possible to eliminate the reactive torque. It can only be minimized to about 2% of the nominal torque. If there is no bevel, the reactive torque amplitude will be as large as one tenth of the nominal torque. It is found that with the externally placed magnets, the considered discrete bevel provides almost complete absence of the reactive torque. It has been concluded that for PMBL motors with closed rotor magnets, it is advisable to have a continuous bevel of the stator core slots per tooth pitch.