Effect of rotor magnetic isolation dimensions on no-load performance of ultra-low speed high torque spoke type permanent magnet motor

This study investigates the effects of rotor magnetic isolation dimensions on the no-load performance of ultra-low speed high torque spoke type permanent magnet motor. The studied spoke type permanent magnet motor structures are shown, where the rotor magnetic isolation parts include a magnetic barrier near the air gap (MB-NAG), a magnetic barrier near the magnetic isolation sleeve (MB-NMIS), a magnetic isolation sleeve (MIS). The magnetic circuit model is performed and the finite element analysis method is used to analyse the no-load performance. Through analysing no-load performance with three MB-NAG shapes, the way to narrow the optimise dimension range considering reducing the cogging torque and increasing the back-EMF synchronously is concluded. The results with different MB-NMIS and MIS dimensions show that: (a) the optimised MB-NMIS dimensions can increase the back-EMF with a thin MIS in a certain dimension range of MB-NMIS, and (b) the increasing proportion of back-EMF influenced by the MB-NMIS is inversely proportional to the thickness of MIS. The feasibility and effectiveness of the proposed motor structure and conclusion are experimentally verified.