Analytical Modeling and Optimization of Pseudo-Direct Drive Permanent Magnet Machines for Large Wind Turbines

Analytical models for the prediction of the flux density distributions in the air gaps, permanent magnets (PMs), and iron regions of large pseudo-direct drives (PDDs) on no-load and on-load conditions are presented. Predictions from the analytical models are compared with those from 2-D finite-element analysis. It is shown that good agreements exist for the flux density distributions in the air, PM and iron regions, the transmitted torque and the torque ripple, as well as the iron loss in the stator core and the pole-pieces. Furthermore, design optimization studies are undertaken in order to determine the effects of the leading design parameters on the efficiency and masses of the active components of the PDD. It is shown that for a direct-drive 10 MW PDD, an efficiency of ~99% can be achieved with a total active mass of less than 65 tons.