Harmonics and powers of doubly fed induction generators at balanced sinusoidal voltages

Wind energy converters feeding into the power grid must comply with standards for harmonics. In practice harmonics or subharmonics caused by the generator are difficult to measure, because the grid itself is also distorted. This paper describes test-bench measurements that are performed with an ideal balanced and sinusoidal voltage source instead of a grid. The results show, which significant frequencies the generator and the converter produce and how they interact with the grid. Sources for these frequencies are explained. The stator side collective power components are calculated and their effect on the time variable asymmetry of the stator current of the three-phase system is investigated.