Contribution of winding space harmonics to average torque in fractional‐slot concentrated permanent magnet machines with equal/unequal teeth.

This study investigates the modulation effects in any m‐phase permanent magnet machines with fractional‐slot concentrated windings and separates the average torque contributed by the winding space harmonics, with particular emphasis on unequal stator teeth. First, winding space harmonics of m‐phase machines with double/single layer windings are analysed and modulation effects of equal/unequal teeth are studied. It is found that, apart from the conventional torque contributed by main harmonic (v = p) and modulated torque by v = p ± Ns harmonics (Ns is slot number and p is pole pair number), additional modulated torque owing to v = p ± Ns/2 harmonic appears in the unequal teeth machines. Then, 12‐slot/10‐pole (12S10P) three‐phase and 10S8P five‐phase machines are employed to verify the analysis through finite element method. It is demonstrated that, for unequal teeth machine, v = p − Ns and v = p − Ns/2 harmonics have positive average torque contribution, around 6.5 and 6% to the total torque. The v = p + Ns and v = p + Ns/2 order harmonics produce negative average torque but with much smaller values. Finally, experiments are carried out on the 10S8P unequal teeth prototype. [ABSTRACT FROM AUTHOR]