Minimizing Cogging Torque in Permanent Magnet Synchronous Generators for Small Wind Turbine Applications

Abstract

Permanent magnet synchronous generators have a wide usage among electric machines, especially in small wind turbine systems. However permanent magnet synchronous generators suffer from cogging torque due to the magnetic interaction between the poles of the rotor’s permanent magnets and the steel laminations of the stator’s teeth. The cogging torque drawback is a major problem in this kind of generators that affects its functionality negatively. In this study the effectiveness of different cogging torque reduction techniques is compared with each other through finite element simulation using JMAG simulation software. Among the different cogging torque reduction techniques, in this study we consider changing the radial shoe depth, shifting permanent magnets, continuous skewing of the rotor or stator, step skewing of the rotor or stator, changing the slot opening width and also having dummy slots. We find that among the considered different approaches, continuous skewing reduces the cogging torque the most. We also find that step skewing of the rotor or stator, changing the slot opening width and having dummy slots can reduce the cogging torque in more or less the same amounts in magnitude. Our results indicate that changing the radial shoe depth has almost no effect in reducing the cogging torque.