Rotor Structure on Reducing Demagnetization of Magnet and Torque Ripple in a PMa-synRM With Ferrite Permanent Magnet

A rotor structure of Permanent Magnet (PM)-assisted synchronous Reluctance Machine (PMa-synRM) with ferrite PM is presented in this paper, in which the irreversible demagnetization of PM and torque ripple are reduced. The bypass rib is proposed and added to the flux barrier of the rotor. The path for the demagnetizing field of armature windings is provided and the torque ripple can also be reduced by the bypass rib. Based on the 2-D finite-element analysis (FEA), the location and dimensions of the bypass rib are investigated and improved. A PMa-synRM with the proposed rotor structure is designed and compared with that using a conventional rotor. The field distributions for different currents are studied to explain the principle of the bypass rib. The results show that the PMa-synRM with the proposed rotor achieves higher antidemagnetization ability and lower torque ripple.