Improved Performance of Series and Parallel Hybrid Permanent Magnet Spoke-type PM Machines Using Tapered Magnets

In this paper, the application of tapered ferrite magnets in spoke-type interior permanent magnet (PM) synchronous machine (IPMSM) with series and parallel configurations of hybrid PMs is investigated. The developed tapered series and parallel hybrid PM spoke-type IPMSMs are designed and compared in terms of electromagnetic performance and rare-earth PM utilization, using the Nissan Leaf 2012 specification. It is revealed that appropriate tapered ferrite magnet configuration is beneficial for enhancing torque per rare-earth magnet volume ratio. Meanwhile, it is shown that the parallel hybrid PM IPMSMs exhibit better performance than the series ones. Comparing to the benchmark, the total PM cost of the proposed parallel hybrid PM design with narrowed ferrite towards the airgap is reduced about 40% assuming that the cost of rare-earth magnet is ten times of the ferrite one.