The use of slightly asymmetrical windings for rotating electrical machines

Historically, asymmetrical windings in electrical machines have been rarely used and only for specified needs, because the adoption of symmetrical configurations has always been considered the only solution during the design stage of electrical machines. The aim of this work is to demonstrate with several examples that the use of slightly asymmetrical windings can be a reasonable choice and, in certain cases, a favorable option during the machine design stage, allowing the possibility of selecting a wider range of slot/pole number combinations, without affecting the performances of the machines. More in detail, an interior permanent magnet synchronous machine equipped with a symmetrical 3-phase winding has been considered as a reference structure. Then, this geometry has been adequately modified in other 3 models to equip asymmetrical windings on each of the modified structures. Afterwards, the performances have been compared in generated torque, magnetic forces, magnetomotive force harmonic content, cogging torque, and iron core losses. This comparison has led to promising results, obtaining in some cases even a reduction of power losses, cogging torque, and harmonic content.