Minimization of EMF Harmonics and Cogging Torque for a Medium Speed RFPM Wind Turbine Generator

There are several methods to reduce EMF harmonics and cogging torque in permanent magnet generators. This paper investigates the influence of magnet embrace optimization and magnet skewing on the performance of a 2.5 MW 400 rpm radial flux permanent magnet (RFPM) wind turbine generator. The medium speed RFPM generator is designed by applying cost optimization to the analytical model and the design is verified using finite element analysis (FEA). The design is modified so that both the induced EMF harmonics and the cogging torque is minimized. According to FEM simulations, optimizing the magnet embrace results in reduction of the total harmonic distortion (THD) of the induced EMF to 1.5 percent whereas step skewing of the magnets reduces the cogging torque below 1 percent of the rated value. Skewing also introduces further improvements on the THD of induced voltage.