Design Optimization, Voltage Quality and Torque Ripple Improvement of an Outer Rotor Permanent Magnet Generator for Direct-Drive Wind Turbines

In this paper, an optimal design for a surface-mounted permanent magnet synchronous generator (PMSG) with outer-rotor is presented to minimize manufacturing cost. The main contribution of this study is to determine new dimensions for surface-mounted permanent magnet (SMPM) that yields  more sinusoidal air gap flux density distribution;  that improves the induced voltage quality, and that reduces both cogging torque and torque ripple. For further investigation, four different plans have been considered for PMSG by combining distributed and concentrated windings with the conventional and proposed SMPM. For this purpose, an accurate model for PMSG is considered. Then, based on this model and intended objective function, design variables were optimized by using genetic algorithm. Afterward, simulation studies based on the finite element analysis (FEA) were carried out in order to validate the optimal plans. By comparing the results of four optimal plans, obtained from optimization process and FEA, we observed that the PMSG with the concentrated winding and proposed SMPM had higher efficiency, lower total volume, lower manufacturing cost, lower cogging torque, and lower torque ripple as compared with other plans. Thus, it can be considered a proper choice for direct-drive wind turbines.