Influence of Demagnetization on Selecting the Optimum Slot/Pole Number Combination for 3MW Surface Mounted Permanent Magnet Vernier Machine

Electromagnetic performance of Vernier machines largely depends on choosing the correct slot/pole number combinations. For a given gear ratio, designs with different slot/pole number combinations are possible. This paper investigates the impact of these slot/pole number combinations on electromagnetic performance such as torque, power factor and demagnetization. The study is carried out through detailed finite element analysis on a 3MW outer rotor direct drive generator targeted at wind power application. The torque/cost, torque/mass and efficiency, which are critical parameters for this application, are compared with a conventional direct drive PM generator. The study shows that Vernier designs with lower values of slot/pole number combinations exhibit much better performance in terms of torque and power factor. However, the potential magnet demagnetization and also core saturation limit these designs and hence play a critical role in selecting the optimal slot/pole number combination.