Finite element analysis of an interior-magnet brushless DC machine, with a step-skewed rotor

The use of finite-element (FE) analysis as a tool for optimising the design of a new form of permanent-magnet electrical machine is described. In order to reduce unwanted torque and generated voltage pulsations, the rotor is divided into a number of separate sections that have both axial separation and different radial positions. FE analysis is employed to optimise: (i) spacer width between the rotor sections, and (ii) radial positioning of sections, in order to give minimum torque and voltage pulsation. In comparison with a single-section rotor, it was found that a 3-section rotor gave an 89% reduction in peak-to-peak torque pulsation. Where possible, the accuracy of the PE method was confirmed by comparison with experimental measurements