Experimental Investigation of Magnet Grouping Technique in Reduction of Cogging Torque and Total Harmonic Distortions in the Axial Flux PM Generator for Direct Drive Wind Turbine

Generators that have been used in direct-drive wind turbines could be produced with a permanent magnet between the power ranges of 1 kW to 1 MW. The cogging torque is the most significant problem of these generators. In this study, the pole grouping method is suggested to reduce the cogging torque of an axial flux permanent magnet (AFPM) synchronous generator with open slotted. The suggested method includes magnetic analyzes and experimental results of the 14-pole open slotted AFPM generator rotor poles that grouped as 7-7, 4-3-4-3, 3-2-2-3-2-2 and named A, B, C, respectively. Besides obtaining the cogging torque (T-c) data, the most considerable part of the study is to get total harmonic distortion (THDV) and output power (Pout) data in which show the electrical performance of the generator for different grouping angles. The optimum ranges for an AFPM generator were determined as 80% reduction for T-c, 15% reduction for Pout, and below 3% for THDV. The optimum grouping angles for A, B, and C were obtained by experimental studies as 32 degrees, 32 degrees, and 30 degrees, respectively. Experimental results and the magnetic analysis have been shown that optimum values are obtained when the ratio of the pole angle to the grouping angle is alpha(r) = 0:75: