Analysis and Reduction of Cogging Torque for Magnetic-Gear PMSG used in Wave Energy Conversion

In order to improve the efficiency and reliability of the wave power system, this paper designs a magnetic-gear permanent magnet synchronous generator (MG-PMSG) for wave energy converters (WECs), which has the advantages of low speed and high torque density. However, high cogging torque harmonics in MG-PMSG windings will occur if the shape of stator and rotor is not optimally designed. In this paper, four methods have been applied to minimize the cogging torque. They are auxiliary slots in stator, skewed stator, Halbach array permanent magnet (PM) and the combination of above three cogging torque reduction techniques (i.e., combination method). Based on finite-element method (FEM), the influence of these four methods on the electromagnetic performances of the MG- PMSG are investigated. The cogging torque and no-load back electromotive force (EMF) are compared and analyzed. Results show that the combination method is the effective way to reduce the cogging torque and voltage harmonics.