Different 600kW designs of an axial flux permanent magnet machine for wind turbines

This work describes the application of a novel axial flux permanent magnet generator with a nominal power of 600 kW for wind turbine applications. The generator is specially designed to have a simple robust construction with a high efficiency, a low weight-to-power ratio and a controlled output voltage over a wide speed range. To prove the feasibility of the concept, a mono-phase prototype was build and tested. Based on the calculation model, various machines were designed for wind turbine applications. Different constructions are presented to fulfill different machine requirements such as power, efficiency, dimensions and weight, both for gearless direct drive systems and for systems with a gearbox. Several conclusions can be made. The direct drive machines are compared with the machines driven by a gearbox. Double sided flywheel generators with a large diameter compared to the length of the machine are compared with double sided stacked generators with a smaller diameter-length ratio. The advantages and disadvantages of high stacked U-cores in combination with rectangular magnets in relation to low stacked U-cores with cylindrical magnets are explained. Finally alternative solutions are proposed in order to further reduce the diameter of the machine.