A method for derating power of a MW directdrive wind turbine permanent magnet generator as over allowable working temperature

Abstract

The use of direct-drive permanent magnet (PM) generators for MW wind application is increasing, because they have higher reliability and less maintenance than geared generators such as geared PM generators and geared induction generators. The price of the direct-drive PM generator is high, taking 10%-15% price of its overall system. Therefore, the generator mush be safely operated to have a long life. For a PM generator, its performance is sensitive to ambient and working temperature so that it needs to be monitored. In this paper, a method is proposed, combining the practical knowledge of a generator and theory to give permissible maximum generated power under certain ambient condition. The stator iron loss of a MW permanent magnet generator in direct-drive wind turbine application is presented as a function of rotor speed or frequency. The generator’s copper loss and electromagnetic torque versus winding temperature and current are investigated. The relationship of voltage, current and active power to the generator temperature is addressed. The given performances can be used to choose the generator’s working parameters such as voltage, current, output power for avoiding generator damaged by over temperature.