Cogging Torque Reduction in Double-Rotor Hybrid Excited Axial Switched-Flux Permanent Magnet Machine

In this paper, a novel double-rotor hybrid excited axial switched-flux permanent magnet (DRHE-ASFPM) machine incorporating the advantages of the axial switched-flux permanent magnet (PM) machine and wound field synchronous machine is investigated. Similar to the switched-flux PM machine, there is a large undesired cogging torque in the DRHE-ASFPM machine because of high air-gap density and strong flux-focusing effect. This paper presents and compares three cogging torque reduction techniques in the DRHE-ASFPM machine, including stator/rotor teeth notching, stator slot chamfering, as well as stator slot chamfering and teeth notching (SCTN). The analytical expression of the cogging torque is derived and three methods are analyzed and compared in detail. As verified by 3-D finite element (FE) method, the SCTN technique can effectively reduce the cogging torque extremely, but slightly decrease the output torque under both PM and hybrid excitation modes. Finally, an optimized prototype machine with SCTN structure is manufactured, and the experiment is performed to validate the FE predicted results.