Wind power plants show different behavior than conventional (synchronous) generators. As the traditional power systems mainly consisted of centralized generation by synchronous machines feeding passive loads, it was well-understood how the system reacted in normal operation as well as during disturbances. As wind power plants are foreseen to increase in size and the amount of installed wind power will grow, the relative contribution of equipment not exhibiting this common behavior increases. At the same time power electronics offer opportunities for additional features to stabilize the power system. Transmission system operators impose requirements on the (dynamic) capabilities of connected new generation resources (including wind power plants) which are specified in grid codes. In this paper, the importance of such requirements is explained by looking at the needs of the power system and by showing simulation results for a test network. The paper facilitates a detailed understanding of the underlying phenomena related to grid code requirements with a focus on low-voltage ride-through and voltage support by reactive current boosting.@en

Solar radiation has a fluctuating nature, especially in oceanic climates where cloud-induced fluctuations are very common. The fluctuations and thus the power system reserve requirements can differ a lot on a daily and hourly basis. In this paper, local hourly classification criteria are defined based upon a spectral analysis of the wavelet transform by using 10 sec solar irradiation data. Three distinctly different classes are identified: overcast, partly cloudy and sunny. The classification is extended to the national scale for 8 sites throughout the Netherlands using 10 min data. Although the nationwide characteristics cannot be described by one single class, the classification still remains meaningful as the fraction of locations with partly cloudy conditions determines the level of fluctuations. Evaluation of the results show the impact of the classification and the consequences for the required system reserves. A combination of the classification method with dynamic reserve allocation is proposed, which should contribute to a more efficient and reliable power system operation.@en

This paper presents an assessment of the kinetic energy reserve that could be made available by aggregating a distributed group of wind farms. The size of reserve available for a single turbine and the range of wind speeds where it can be assumed available is computed and compared with the kinetic energy delivered by synchronous generators during typical transients. The size and availability of an aggregated reserve is then computed using wind speed data from 39 locations on and off the shores of the Netherlands. The dependence of this reserve on the area and density of sites being aggregated is presented. Finally, the aggregated reserve is compared on a statistical basis with the energy required for 87 frequency dip incidents in the European continental grid. It is concluded that although improved communications and control would be necessary, the technical potential could meet or exceed the need for inertial response forty percent of the time.@en