Asymmetrically Chorded Multi-Layer Winding and Slot Design for Suppressing Space Harmonic Effects in Induction Motors

In previous studies, the first method to eliminate unwanted space harmonic effects in asynchronous motors is chording. However, it is possible to make winding changes in a way that can target a single harmonic within chording and only covers a certain amount of winding change while causing a decrease in the fundamental. There are other techniques that can further reduce the harmonic content in cores having evenly distributed symmetrical slots by altering the winding distribution, slot and teeth shape both in stator and rotor sides. Furthermore, there are previous studies using unevenly distributed slots and number of turns per slot for single layer windings. This manuscript presents a new approach to further reduce winding harmonics in unevenly distributed slots and number of turns per slot for multi-layer windings those obtained by the prepared optimization algorithm that introduces the use of unequal coil-pitches at least for 2 winding layers. It was shown that the optimization method obtains new slot positions and the number of turn values for each slot for the specified ampere-turn value to obtain a magnetomotive force (MMF) distribution that contains fewer harmonics than any traditional or special winding arrangements while still maintaining a high fundamental winding factor. The new technique was applied to the design of a 3-phase, 36-slot 2 pole 4 kW squirrel cage induction motor and important features of the design are given in comparison with those of a standard machine, demonstrating the pros and cons of the method.