Study on fractional slot permanent magnet synchronous machine for wind turbines

This paper studies the application of fractional slot winding for permanent magnet synchronous generators, which are being widely used in wind turbine systems. A 3kW axial flux permanent magnet synchronous generator is chosen when studying the winding design. The fractional slot winding is studied first in terms of number of periodicity of machine, the greatest common divisor of N_s and N_p, period of cogging torque, the winding factor by using star of slots. The machine is then designed with both fractional slot 12/10, 18/16, 18/20 and 24/20 and integral slot 30/10, with same electric loading and magnetic loading, resulting in similar machine dimensions. Parameters including phase resistance, back-EMF and inductance of candidate slot/pole combination are calculated and compared. The influence of winding design to performance of PM generators is studied when generator is connected to a diode rectifier or forced-commutated rectifier. The performances are evaluated in d-q coordinates and compared with integral slot winding (q=1).