Directly driven wind turbine generators

This paper deals with directly driven generators forwind turbines. The aim is to discuss the efficiency,active weight and the size of a 30 rpm 500kWpermanent magnet generator. An analytical designmethod for the generator is used together with acost function to optimize the generator. Theinfluence of the cost function on the optimumgenerator is investigated. The investigation showsthat the efficiency depends mostly on the slot heightand, therefore, a high efficiency leads to a highactive weight. The generator diameter will probablyhave to be more than 2 m because of the cost of theactive material, but above that diameter the optimumsize can be expected to be mostly determined by thecost of the supporting structure. This type ofgenerator has a higher average efficiency than aconventional four-pole induction generator and gearand it can probably be lighter