Analysis and Design of Triple-Rotor Axial-Flux Spoke-Array Vernier Permanent Magnet Machines

This paper focuses on the analysis and design of a triple-rotor axial-flux spoke-array vernier permanent magnet (TR-AFSAVPM) machine. By cooperating with spoke-array rotor and coil-wounded winding, power factor and torque density of the proposed machine are much improved and its copper utilization is reduced comparing with conventional vernier machines. First, the machine structure and its operation principles are reviewed. After that, analytical equations of its back-electromotive force and torque are derived to reveal the machine characteristics. Based on both quasi-3-D finite element analysis (FEA) and 3-D FEA, its high torque density performance is verified and a set of optimized machine sizing specifications is ultimately settled. A fractional slot axial-flux permanent magnet (VPM) machine and an axial-flux surface VPM machine are designed to compare with the proposed configuration. Analysis results show that the TR-AFSAVPM machine has high power factor viz., 0.96 and high torque density viz., 24.2 kNm/m³. A prototype has been designed and tested to validate the results. No-load test result is illustrated in this paper and the rated load experiment will be added in the future.