Performance Analysis and Mechanical Assembly Considerations for a Spoke-Type Permanent Magnet Vernier Machine with an Inner Salient Pole Core on the Rotor

As the world is currently undergoing an energy transformation paradigm—replacing the high carbon, finite supply coal and natural gas with renewable wind and solar electricity production—the search for high torque density permanent magnet (PM) electrical machines for direct-drive wind energy systems has been unprecedented. Consequently, various innovative topologies of the inherently magnetically geared PM vernier machine have been developed. Notable among these is the ‘alternating flux-barrier’ topology which was developed to mitigate the excessive harmonic flux leakage due to opposite magnetization directions of adjacent spoke PM pairs. However, this modified Spoke-Type PM vernier machine (STPMVM) is yet to gain industry-wide acceptance owing to the perceived negative effects of higher order harmonics created through flux-focusing. This paper presents a comprehensive analysis of the performance characteristics of STPMVMs, highlighting the inherent conflict between torque capability and power factor from the perspective of effective magnetic loading and coefficient of power factor (PF). The underlying reasons for the poor PF characteristics discussed in this paper have been lacking in previous studies. The paper also discusses PF improvement through Multi-Objective Optimization, as well as mechanical assembly considerations to alleviate concerns about manufacturing complexity of the modified STPMVM.