Aggregated wind turbine models for power system dynamic studies

The interaction between a power system and a wind-farm can be studied using either a simplified 'aggregated' or a complex 'detailed' model. The detailed-model results compare well with the actual, therefore, provided that both models have similar dynamic characteristics, the aggregated model provides a rapid and cost-effective way of representing large wind-farms in power system dynamic studies. A brief overview of windfarm aggregation methods is given and their application in power systems analysis is discussed. Aggregation techniques are then applied to a wind-farm with thirty wind turbines. It is shown that the aggregation of the swing equation and equivalent representation of network and generator impedances can be used for aggregated representation of fixed speed wind turbines. A similar approach applied to the d- and q- axis controller of a doubly-fed induction generator (DFIG) failed initially to provide satisfactory dynamic characteristics with the aggregated model. Consequently, a simple method was used to scale the rotor currents of the controller, so the dynamic characteristics with DFIGs became acceptable.