A Generic Approach to Reduction of Magnetomotive Force Harmonics in Permanent-Magnet Machines With Concentrated Multiple Three-Phase Windings

This paper proposes a generic approach to reduction of magnetomotive force (MMF) harmonics in permanent-magnet machines with multiple three-phase concentrated windings. Analytical equations for the MMF distributions of the proposed multiple three-phase concentrated windings are derived, and the principle for harmonic cancellation is established and validated by finite-element analysis. A new 18-slot 14-pole nine-phase winding machine in which all sub-MMF harmonics are eliminated is presented based on the proposed generic approach. The proposed approach is also applicable to other slot-pole combinations with concentrated windings except for slot number being equal to 1.5 times the pole number. Retaining all the advantages of the concentrated windings, the new technique improves the fundamental winding factor, enhances the fault tolerance capability, and reduces the detrimental effects of lower and higher order MMF harmonics on the machine, such as high rotor eddy-current and iron losses, less reluctance torque, acoustic noise, and vibration.