In recent years, the amount of wind turbines in the power system has increased tremendously. As the current wind turbines do not participate in the provision of ancillary services such as frequency control and voltage control, this may compromise the proper functioning of the electric power system. However, since the modern wind turbines are equipped with a power-electronic converter, they can assist in the provision of ancillary services. To achieve this, additional control loops have to be added to the wind turbine controller. In this paper, an overview of the different ancillary services is given. The ability to provide them with wind turbines is discussed. Since frequency and voltage control are the most important, these two services are further elaborated. It can be concluded that wind turbines are suited
to provide frequency control, especially when they are operated slightly below their maximum power point. They can also assist in voltage control, while operation in the maximum power point is usually possible, so few energy is lost. These are important outcomes, since wind turbines which provide ancillary services can contribute in allowing a higher penetration of renewable energy in the power system without compromising its proper functioning
