Design of a radial flux permanent magnet wind generator with low coercive force magnets

In this paper, the design procedure of a three-phase radial flux permanent magnet synchronous generator (PMSG) is presented for a wind turbine application. This generator is intended for direct coupling to a wind turbine. Low coercive force AlNiCo permanent magnet (PM) material is used in place of common and costly NdFeB PMs. The low coercive force of AlNiCo PMs may result in demagnetization of the PMs when conventional structures of a PM machine is used. This occurs due to the demagnetization magneto-motive force due to stator currents under load conditions of the machine. This may result in irreversible change in the PMs and also unstable operation of the machine, which is the main problem in using AlNiCo PMs in PMSG design. This can be resolved through alternate rotor design that aims to achieve flux intensifying operation. Moreover, the optimal number of slot/pole/phase is determined for cogging torque reduction and generator performance improvement. In this paper, a design detailed approach is formulated and presented, achieves the afore-mentioned characteristics. Finally, the precision of the analytical design approach of the PMSG is validated by means of detailed finite element computations.