Loss sensitivity of a parallel wound low voltage airgap winding PM generator for offshore wind turbines

This paper investigates power losses due to circulating currents of a low voltage axial-flux air-cored airgap permanent magnet generator. Both broad and narrow tolerances for the design, material and manufacturing process of the generator were investigated to assess the sensitivity of tighter build tolerances on the magnitude of the circulating currents. Aspects of the generator design that were analysed include the height of the permanent magnets, the magnet maximum energy product, and the separation between the two rotor plates. Variations in the magnet maximum energy product between the parallel windings resulted in the largest circulating currents for studying the individual variables. By combining the variations in magnet energy with variations in magnet height and rotor plate separation, the circulating currents were intensified with a calculated average loss of 19 kW. The study highlights the importance of careful design parameters and tolerances in an effort to minimize power losses and reduce losses in revenue over the lifetime of the generator