Effects of Radial Divided Magnet Shifting on Cogging Torque of Axial Flux Permanent Magnet Generator for Small Scale Wind Turbine

Transitioning energy sources from fossil fuels to renewable energy is demanding currently due to global warming issues. Those require advanced technology of each component that supports renewable energy to achieve high efficiency, for example, permanent magnet generator (PM generator) for wind power plants. PM generator is widely known for high efficiency, high energy density, low maintenance, and simplicity. Although a PM generator has a lot of advantages, it still has drawbacks specifically for cogging torque generated between the permanent magnet and stator core which causes vibration and decreases the net torque from the shaft due to its counter direction from the rotor direction. Several methods have been proposed to reduce cogging torque such as traditional skewing magnet, selecting appropriate slot opening, pole arc to pole pitch ratio arrangement, and placing flux barrier between 2 slots. This paper discusses the implementation of radially divided magnet shifting to axial flux PM generator with yokeless and segmented armature configuration. The impact of magnet shifting on reducing the cogging torque is also discussed. The proposed design is a permanent magnet divided into 2, 3, 4, and 5 parts and shift the magnet with a common angle respected to the inner side of the magnet. 3D finite element analysis is performed to analyze and simulate the axial flux PM generator model. An Analytical approach is discussed further to satisfy the relationship between magnet common angle and generated cogging torque. The results show that higher number of divided permanent magnet leads to decreased cogging torque, although the smaller size of permanent magnet will be challenging in manufacturing process.