1 Risø National Laboratory for Sustainable Energy, Technical University of Denmark2 Department of Electrical Engineering, Technical University of Denmark
In many parts of the world and certainly in Europe large areas exist where the wind resources are good or very good and the grid is relatively weak due to a small population. In these areas the capacity of the grid can very often be a limiting factor forthe exploitation of the wind resource. There are two main problems concerned with wind power and weak grids. The first is the steady state voltage level. When the power consumption is low e.g. during the night the voltage of the grid can increase tolevels above the limits if the wind power input is high. The other main problem is voltage fluctuations. Because the wind is fluctuating the output from the wind turbines is also fluctuating. This together with wind turbine cut-ins can result in voltagefluctuations that are above the flicker limit. Some or all of the these problems can be avoided if a so-called power control concept is applied together with the wind farm. The idea behind the power control concept is to eliminate the violations of thesteady state voltage level by buffering the power from the wind turbines in periods where the voltage limits might be violated and then release it when the voltage level is lower and combine this ability with smoothing of the power output in order toremove power fluctuations that otherwise would create voltage fluctuations above the flicker limit. The project consists of three parts: investigation of the general applicability of the power control concept, design, implementation and testing of abattery based prototype and two case studies. In order to assess the general applicability of the concept a framework has been formulated in which the different options (power control concepts, grid reinforcement and dumping of surplus wind energy) canbe compared. As part of this, models have been developed, that can assess the voltage fluctuations and the steady state voltage behaviour for the different options. The investigations have shown that the power control concept can compete with gridreinforcement and usually the dumping of wind energy will be the most expensive option (in the case where rather large amounts of wind energy are installed). The prototype of a socalled ‘add-on’ power controller has shown that it is possible to controlthe output from the combined system so that the fluctuations in power are much reduced and at the same time the reactive power is controlled to a desired value. The two case studies (Madeira, Portugal and Co. Donegal, Ireland) revealed that sometimes theleast cost and most attractive option is change in the operating strategy of the power system. This allowed that further wind energy can be integrated at competitive cost in the Madeira power system. In Co. Donegal the options for pumped storage are goodcombined with good wind resources. Unfortunately the grid is weak. The least cost option for the feeder studied is either grid reinforcement or a power control system based on pumped storage if rather large amounts of wind energy are to be absorbed by thepower system. The cost estimates for the two options are in the same range. The current report is a summary of the work done in the project 'Power Control for Wind Turbines in Weak Grids'. The project has been partly funded by EU under contractJOR3-CT95-0067.
Vindenergi og atmosfæriske processer; Risø-R-1117; Risø-R-1117(EN)