Coil Excited Pseudo Direct Drive Electrical Machines

A pseudo direct drive (PDD) equipped with a coil-excited high-speed (HS) rotor is presented. An analytical model which predicts the flux density in the air spaces and the permanent magnets (PMs) of the PDD is presented, and it is shown that good agreement exists between the analytical and finite-element predictions. Furthermore, the model is employed to investigate the effects of the key design parameters on the performance of a coil-excited PDD for a 10-MW wind turbine application, and an optimized design is proposed. It is shown that shear stress in excess of 100 kPa can be achieved, and that compared with a PM-excited PDD, a reduction in PM mass can be realized. It is also shown that the efficiency over the operating range of the wind turbine can be maximized by adopting an appropriate control strategy of the HS rotor excitation currents.