Design a New Hybrid PM Machine with a Low Cogging Torque by Attaching Permanent Magnets on Rotor Surface

In a hybrid variable-flux permanent-magnet synchronous machine (VF-PMSM), the distribution of air-gap magnetic field is also different under different magnetization states and it faces difficulties for traditional methods to solve the problem. This paper proposes a new machine that is adaptive under different magnetization conditions. A finite element simulation model is built and the result of a comparative study is presented. In order to investigate further the impact of the addition of permanent magnets on the rotor surface, the proposed machine is compared with other methods for reducing cogging torque, as well as with a PM Machine featuring a smaller air-gap length. The result shows that the proposed machine is effective to reduce the cogging torque in both enhanced and weakened magnetization states.