Scaling of Pseudo Direct Drives for Wind Turbine Application

An analytical model for the prediction of the magnetic field distribution in the air gaps and permanent magnet (PM) regions of a pseudo direct drive (PDD) is presented in scale-invariant form for magnetizations only dependent on the circumferential coordinate. The scale-invariance of the model is then employed to discuss the scaling laws of the PDD and investigate the effects of scaling on the efficiency and the mass of the various active components, i.e., copper, PM, and lamination materials for large wind turbines with powers between 5 and 20 MW. It is shown that, with the exception of the copper winding, the masses per megawatt of the steel laminations and the PMs are increased when the power rating of the wind turbine is increased.