Application of Phase Shifting Technique for Reducing the Magnetomotive Force Space Harmonics of Tooth Concentrated Windings

Permanent magnet machines with fractional slot concentrated windings are very attractive for low-speed direct-drive applications due to their compactness, cost effectiveness, and high efficiency. However, one of the key challenges of using concentrated winding configurations is the high content of space harmonics in the air-gap magnetomotive force distribution, which can lead to undesirable effects such as high rotor losses, vibrations, and noise. In this article, the phase shifting technique is investigated to deal with the harmonic content of such windings. An example of application is given for a three-phase winding with a number of slots per pole per phase = 2/5. It is shown that by using this simple technique, one can cancel some of the harmful magnetomotive force space harmonics without decreasing the winding factor of the torque producing harmonic. Further, calculations revealed a significant improvement in machine performances when compared to the conventional design.