Characterization of radial magnetic forces in low-speed permanent magnet wind generator with non-overlapping concentrated windings

This paper aims to describe the characteristics of the radial magnetic forces in a low-speed permanent magnet (PM) machine with concentrated windings. Magnetic flux distribution in the airgap is calculated using finite element method and the results are employed to compute the radial forces using Maxwell's stress tensor. The flux density due to PM and MMF magnetic fields and their interaction and also effect of slotting are discussed. Radial forces are investigated in no-load and load conditions. The authors have tried to address the importance of the slot harmonics in the force characteristics. It is shown that the amplitude of the lowest vibration mode is considerable even in no-load, however it increases while the machine is loaded, leading to higher vibration level. The influence of considering the tangential flux density on the force calculation is also investigated. It is found that in the case of neglecting tangential flux component, the level of calculated radial magnetic forces decreases considerably.