Multiobjective Optimal Design of an Axial Flux Permanent Magnet Generator for Directly Coupled Wind Turbines

Factors such as high efficiency, high power density, the possibility of realizing a compact multistage machine and the feasibility of applying a large number of poles make the Axial Flux Permanent Magnet (AFPM) generators highly appealing for use as low speed wind power generators. This study puts forth a multi-objective optimization of the efficiency and power density of a low speed AFPM synchronous generator. The optimization problem was formulated by means of general sizing equations and then Genetic Algorithm (GA) was utilized. This study uses a weighted fitness function which offers a tool for ascertaining the priority of objective functions. This fitness function includes two variables whereby an increase in either of them leads to more improvement in one of the objective functions than in the other. The merits of this method are especially palpable in situations where it is necessary to prioritize the objective functions as is indeed the case with generators used in wind turbines which should have not only a high efficiency but also a reduced weight and volume. Finally, the results are verified through the three dimensional Finite Element Method (3D-FEM).