A low speed, high-torque, direct-drive permanent magnet generator for wind turbines

There is a market for small, efficient and cost-effective wind generators for mini-grid and remote power systems. Direct-drive permanent magnet generators have become very attractive for this application. This paper describes the improvements achieved in an outer-rotor direct-drive permanent magnet generator by using finite element analysis and optimisation techniques. The starting torque of the generator is studied. An optimisation routine for the design, including magnetic finite element analysis and lumped-parameter thermal model, is presented. A prototype for 20 kW, 211 rpm generator was built. The test results with a resistive load confirm the satisfactory operation of the generator. Compared with the previous prototype, the new design has lower mass, lower starting torque and improved efficiency.