Analytical model of open-circuit characteristics of two-layer spoke-type ferrite interior permanent magnet machines

Two Dimensional (2D) analytical methods are developed based on effective yet simple magnetic circuit models for the two-layer spoke type ferrite interior permanent magnet (IPM) configured machines. Due to the low residual flux density of ferrite magnets, conventional spoke type machines with flux-focusing structure are usually proposed to increase flux density. However, the spoke type machine contains considerable amount of harmonic contents. Thus multi-layer configurations are used to improve the flux distribution in the airgap and back EMF. The analytical model for a spoke type configuration is firstly developed, and the model for the two-layer configuration is established accordingly. To improve the accuracy of the models, higher order harmonics are also included. Then, the influence of the size and location of permanent magnet (PM) poles are investigated. Finally, the models are validated by both finite element analysis (FEA) simulations and experimentations.