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

SUVIRE, GASTÓN ORLANDO; MERCADO, PEDRO ENRIQUE

Dynamic Modelling

INTECH

Lugar: Vukovar; Año: 2010; p. 189 - 208

Wind power generation is considered the most economic viable alternative within the portfolio of renewable energy resources. Among its main advantages are the large number of potential sites for plant installation and a rapidly evolving technology, with many suppliers offering from individual turbine sets to 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. 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 related to wind power and weak grids is voltage fluctuations. Several factors contribute to voltage fluctuations in the terminals of a wind generator: aerodynamic phenomena (turbulence in the wind, tower shadow, etc.), short circuit power in the connection point, number of turbines and 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 generators. Taking into account these aspects, it is important to evaluate the information provided by models that simulate the dynamic interaction between a wind farm and a power system. Such models provide valuable information and enable to perform the necessary preliminary studies before connecting wind farms to the grid. The purpose of this chapter is to show the complete dynamic modelling of a wind power conversion system. Various wind farm models to be used in dynamic studies of power systems are analyzed, and one of them is presented and explained in detail. This model takes into account the dynamic behaviour of the wind turbine and the coincidence effect of the wind farm (i.e. the power fluctuations of a wind farm are relatively smaller than that of a single wind turbine). Moreover, the used models of wind speed and wind turbine are presented. The wind speed model involves the modelling of wind speed as a random process taking into account the main parameters of the wind such as: standard deviation, mean wind speed and turbulence length scale. The wind turbine model is carried out with a simplified model based on an equivalent transfer function, which represents dynamically the wind power generation as a function of the wind speed in each simulation step. To show the impact of the wind farm into a weak power system, various case studies are simulated. These cases represent different operation states of the wind farm which cause voltage fluctuations in the connection point with the grid. Validation of models and simulations of the interactions between the wind farm and the power system are carried out by using SimPowerSystems of SIMULINK/MATLAB™.