Saliency ratio derivation and optimisation for an interior permanent magnet machine with concentrated windings using finite-element analysis

The implementation of concentrated windings in interior permanent magnet (IPM) machines has numerous advantages over distributed windings, with a major disadvantage being the decrease in saliency ratio. Theoretically, this would result in a lower field weakening range which is undesirable for traction applications. Although it is revealed in some studies that concentrated winding results in lower saliency ratio, experimental techniques used for accurately acquiring the saliency ratio of IPM machines with concentrated windings are yet to be fully understood. This study presents a proposed finite-element (FE) method, which is derived from the experimental AC standstill test method. With this method, the d- and q-axis inductances (L-d and L-q) of the IPM machine with fractional-slot concentrated windings can be accurately determined. Limitations of this method are discussed. Subsequently, this method is used to determine L-d and L-q of various winding configurations and rotor designs. From repeated FE testing using Flux2D, the authors derive a set of general rules for optimising the saliency of an IPM machine with fractional-slot, single-layer concentrated winding.