Skewing of stator windings for reduction of spatial harmonics in concentrated wound PMSM

In Surface Permanent Magnet (SPM) Synchronous machines with fractional slot concentrated windings (FSCW) configuration, few slot/pole combinations exhibit large spatial harmonic and sub-harmonic fields. Spatial harmonics result in distorted voltage waveforms and cause additional losses thereby deteriorating the machine's performance. From background literature, it has been found that these harmonics are reduced by increasing the number of winding layers, increasing the number of phases, or introducing complicated magnetic flux barriers in the stator core, thereby reducing the overall torque density of the machine. This paper presents a method to minimize the effects of spatial harmonics by skewing the stator windings without reducing the torque producing harmonic component. Further, the impact of stator winding skew is studied on magnetic force, open-circuit phase voltage, inductances and cogging torque using a novel analytical model incorporating higher order harmonics in air-gap flux density and phase inductances. Comparative analysis of skewed machine is performed with the experimentally obtained results for a baseline un-skewed machine.