Permanent Magnet (PM) machines with concentrated windings are cost effective, compact and highly efficient. The application of such machines in large Direct Drive (DD) wind turbines can be advantageous. However, these machines have the problem of eddy current losses in solid parts like magnets and rotor backiron. Apart from cooling problems, these eddy current losses might lead to de-magnetization of PMs because of excessive heating. This paper presents an analytical model for eddy current loss calculation in magnets and solid back-iron of large wind turbines of MW rating. The analytical model has been derived from 2-d magnetic vector potential. The effects of simplifying assumptions have been quantified by comparison with Finite Element (FE) simulations. The analytical model over-estimates the losses in magnets while losses in rotor back-iron are underestimated. However, the total losses are accurate within 9% of FE calculation. The analytical model is very fast and generic whereby this model can serve as a tool for design optimization where eddy current loss is a criterion. A design with 9 slots per 8 poles has acceptable eddy current losses while in a 3 slots per 4 poles design losses are unacceptable.@en

Permanent Magnet machines have a high force density and high efficiency. These machines can be made cost effective by using fractional-pitch windings as the fabrication of such windings can be automated. However, one big challenge to design such machines is to analyze the eddy-current losses, specifically in solid back-iron of the rotor/translator and magnets. This paper compares analytical calculation of eddy current losses with Finite Element (FE) calculation. The model is applied to calculate the losses in the solid back-iron of the linear PM generator of the Archimedes Wave Swing (AWS) for different combinations of number of poles and teeth. It was concluded that Eddy current losses in analytical model are over estimated for lower order harmonics and under estimated for higher order harmonics. The total losses however for both analytical and FE methods were found to be similar. Thus, the analytical method can be used to compare eddy current losses in topologies with different slot-pole combinations.@en

A direct drive generator used in wind turbine has high energy yield compared to other drivetrain topologies and low maintenance is expected as the technology matures. On the other hand direct drive generator weight and size increases rapidly when scaled up to larger units. This paper will investigate the possibility of weight reduction of large direct drive generator using magnetic bearings without compromising maintenance. Three different configurations using magnetic bearings i.e. single magnetic bearing concept, flexible rotor and hybrid concept have been analyzed. The results show that a combination of magnetic bearings and mechanical bearing with stiff radial structure and axial flexibility i.e. hybrid concept has the possibility to reduce weight of direct drive machine significantly compared to conventional design.@en