Analysis and Experimental Evaluation of Harmonic Leakage Inductance for Polyphase PM Machines Having Close Slot and Pole Combinations

For fractional-slot concentrated winding permanent-magnet (PM) machines having close slot (Q) and pole (p) combinations, harmonic leakage inductance could be several times higher than magnetizing inductance, resulting in a low power factor and a small characteristic current. This paper tends to extend the investigation of harmonic leakage inductance to polyphase PM machines, which have been receiving great attention in safety-critical applications. The impact of phase belt and winding layer on the winding distribution factor, which is usually neglected in previous work, has been investigated. The inductance index as well as a completed calculation flowchart has been introduced, in order to offer a full picture of harmonic leakage and its impact on winding inductance. Five-phase and six-phase schemes with different slot/pole combinations have been investigated as examples for odd and even phase number machines, respectively. Furthermore, several prototype machines, including three-phase 12-slot/10-pole and six-phase 24-slot/22-pole single-layer and double-layer machines, were fabricated, and experimental verification has been conducted.