Novel Method to Minimize the Air-Gap MMF Spatial Harmonic Content in Three-Phase Windings

Most of industrial induction motors currently used employ simple winding patterns, which commonly are designed to fulfil the fundamental magnetizing flux and torque requirements, disregarding the spatial harmonic content of the air-gap magnetomotive force (MMF). However, it is well known that the lower-order MMF spatial harmonics have a negative impact on the motor efficiency, vibration, noise, and torque production. The use of different turns per coil in the winding design is a possible solution to mitigate the problem. In this paper, a novel winding optimizing algorithm is fully described. The air-gap is modelled as a linear function of the current-sheet created by the conductors in the slots. Several winding patterns with different poles for stators with different slots are optimized, and the turns per coil pattern is presented in tables for single and double layer windings with optimal coil pitch shortening. These tables can be used, as reference, in winding design projects. An application example of winding optimization is also presented.