Design of a Fractional Slot Multi-Phase PMSG for a Direct-Drive Wind Turbine

The design of a Permanent Magnet Synchronous Generator (PMSG) suitable for off-shore direct drive wind energy conversion systems (WECSs) is presented in this paper. In particular, a twelve-phase PMSG, characterised by a surface mounted permanent magnet configuration and by outer rotor layout has been considered with the aim of improving torque quality, energy efficiency, power management, fault tolerance and reliability of WECS. For these purposes, fractional slot multiphase windings have been asymmetrical distributed in order to form four three-phase independent subsystems. Finally, a specific design procedure oriented to minimize cogging torque and to maximize magnetic decoupling of each three-phase subsystem has been developed. The analytical procedure and the corresponding results have been reported and validated by means of Finite Element Analysis (FEA), highlighting the worth and effectiveness of the proposed configuration.