Axial Flux Permanent Magnet Generators for Direct-Drive Wind Turbines - Review and Optimal Design Studies

This paper presents a comprehensive analysis of the feasibility, cost, and electromagnetic performance of five distinct types of axial flux permanent magnet (AFPM) generators designed for direct-drive wind turbines. The generator configurations investigated include a single-sided AFPM generator with a surface-mounted PM rotor (AFPMG), a double-sided AFPM generator featuring PMs on the stator and a reluctance rotor (AFPMG-RR), a coreless stator AFPM generator with surface PMs (CAFPMG-SPM), and a coreless stator AFPM generator with a Halbach PM array rotor (CAFPMG-Hal). Each generator's operating principles and configurations are thoroughly explained and compared. Large-scale multi-objective design optimizations were conducted on each type, taking advantage of symmetric computational models and using a differential evolution algorithm based on 3D finite element analysis (FEA) to minimize cost and mass while maximizing efficiency for all designs. A comprehensive discussion of the optimization results highlights the merits of each configuration. The findings indicate and confirm that AFPM generators can potentially achieve superior performance compared to their radial counterparts, as reported in the literature, while also benefiting from more robust and compatible mechanical integration with wind turbines.