Dynamic Modelling of a Wind Farm and Analysis of Its Impact on a Weak Power System

Wind power generation is considered the most economic viable alternative within the portfolio of renewable energy resources. Among their advantages are the large number of potential sites for plant installation and the rapidly evolving technology with many suppliers offering from the individual turbine set to even turnkey projects. On the other hand, wind energy projects entail high initial capital costs and, in operation, a lack of controllability on the discontinuous or intermittent resource. In spite of these disadvantages, their incorporation is growing steadily, a fact that is making the utilities evaluate the various influencing aspects of wind power generation onto power systems. Throughout the world there are large scarcely populated areas with good wind power potential where the existing grids are small or weak, due to the small population. A typical example is the large expanse of the Argentine Patagonia, with small cities clustered on the coastal areas and the Andean valleys. In these areas the capacity of the grid can very often be a limiting factor for the exploitation of the wind resource. One of the main problems concerned with wind power and weak grids is the voltage fluctuations. Several factors contribute to the voltage fluctuations in the terminals of a wind turbine generator (Suvire & Mercado, 2006; Slootweg & Kling, 2003; Ackermann, 2005; Chen & Spooner, 2001; Mohod & Aware, 2008; Smith et al., 2007): the aerodynamic phenomena, i.e., wind turbulence, tower shadow, etc.; the short-circuit power at the connection points; the number of turbines and the type of control. Besides, wind turbines may also cause voltage fluctuations in the grid if there are relatively large current variations during the connection and disconnection of turbines. With these aspects in mind, it turns necessary to ponder the information stemming from models that simulate the dynamic interaction between wind farms and the power systems they are connected to. Such models allow performing the necessary preliminary studies before connecting wind farms to the grid. The purpose of this chapter is to show by means of simulations the voltage fluctuations caused by a wind farm in a weak power system. A model for dynamic performance of wind farms is presented, which takes into account the dynamic behaviour of an individual wind turbine and the aggregation effect of a wind farm (i.e., the larger the wind farm, the smoother the output waveforms). In addition, the wind speed model and wind turbine models are briefly presented. Validation of models and simulations of the interactions between the wind farm and the power system are carried out by using SimPowerSystems of SIMULINK/MATLABTM.