Effect of stator shifting on harmonic cancellation and flux weakening performance of interior PM machines equipped with fractional-slot concentrated windings for hybrid traction applications

Electrical drive systems, which include electrical machines and power electronics, are a key enabling technology for advanced vehicle propulsion systems that reduce the petroleum dependence of the ground transportation sector. To have significant effect, electric drive technologies must be economical in terms of cost, weight, and size while meeting performance and reliability expectations. Interior Permanent Magnet (IPM) with fractional-slot concentrated-windings have been shown to be good candidates for hybrid traction applications. One of the key challenges is the additional stator mmf sub- and super-harmonic components that lead to higher losses in the rotor as well as saturation effects. This paper tries to address this issue by looking into the concept of stator shifting to cancel out the harmonics in fractional slot concentrated windings, while also considering the flux weakening performance under such effects. The novel aspects of the paper will be highlighted in the introduction section. The concept of stator shifting will be explained, the effect of varying the shift angle on the various harmonic components and winding factors will be investigated. Various designs, arising out of single layer and double winding layer 10-pole, 12-slot configuration along with double winding layer 16-pole, 18-slot configuration (targeting the FreedomCAR specifications), with varied shift angles are evaluated. The comparison between these designs in terms of their power density, efficiency and torque ripple is presented.