Performance and efficiency comparisons for interior PM and flux-switching PM machines with ferrite magnets for automotive traction applications

This paper investigates the efficiency and performance of three permanent magnet (PM) machines with different topologies when all three use the same ferrite magnet material and are optimized to meet the same set of automotive traction specifications with a minimum total active mass. The three machine topologies are an interior PM (IPM) machine, a conventional flux-switching PM (FSPM) machine, and a PM-sandwiched FSPM machine. The three machines are compared using a number of criteria including total active mass, component material mass values, and several geometric parameters. Both FSPM machine types exhibit significant efficiency benefits compared to the IPM machine, but the magnet content of these two machines is also much higher. The ramifications of these efficiency and magnet content tradeoffs are explored as they apply to an electric vehicle application. Experimental results from a demonstrator PM-sandwiched FSPM exhibit good agreement with predicted results when three-dimensional finite element analysis is used to properly incorporate axial leakage flux at the two ends of the FSPM machine core.