Development of methods and models for assessing voltage stability in power systems with a high penetration of power generation from renewable sources
Final Report Abstract
Due to the German social and political request for constitutional changes in the power system to a renewable electricity generation, the generation system in Germany has changed during the past years and will further change in the upcoming years. The feed-in from renewable energy sources (RES) is growing rapidly in the system and thus replaces conventional fossil power plants. Power plants for renewable energy sources are installed at locations with a high yield of primary energy, which leads to higher transmission distances between sources and loads within the power system. Furthermore, assets are mainly installed in the distribution networks due to their small rated power output. These developments cause a general increase in the reactive power consumption at all system levels, while the flexibility of controlling active and reactive power is reduced. Voltage stability of power systems is defined as the ability to maintain steady voltages in the system while and after being perturbed. Due to the changing environment, voltage stability must be evaluated under special consideration of distribution grids and feed-in from RES. Voltage collapse is the process leading to non-operable low system voltages across a part or across the entire power system which has to be avoided by all means. In literature there are many different methods to evaluate voltage stability in power systems. In power system planning lots of different system situations need to be assessed, like different load and generation dispatch situations as well as changing network topologies. The continuous changes of the generation structure in the European power system force transmission and distribution system operators to adapt to new system situations. In all today’s methods the only explicitly addressed driving force for voltage instability is the change of loads. But in future, renewable generation may become critical for voltage stability due to higher average transmission power and distance. Therefore, the focus of this project was the development of an enhanced method to assess voltage stability. This was done by extending the well-known method of the Continuation Power Flow. With the developed methods and models it is possible to identify and analyze multiple aspects of an existing or prospective transmission system. These are especially voltage stability limits, weak system areas and critical contingencies. Besides, the method can be used to assess the maximum integration of renewable energies for various load situations as well as best- and worst-case power plant dispatch. To develop the analyzation tool, new models and an upgrade of existing methods were required. This was done in three working packages. In the first working package the actual method, a steady-state multi-dimensional method for voltage stability assessment was developed. As the active and reactive power characteristics of distribution systems will change because of increasing installation of renewable energies, a new model to consider the influence of distribution systems was developed in the second working package. Content of the third working package is a heuristic approach to assess different power plant dispatch situations and their influence on voltage stability limit. The newly developed method was exemplary applied to investigate certain scenarios of the German power system, considering the influence of the European power system. The investigation showed a significant influence of distribution networks on voltage stability limit. If in the upcoming years further assets are controlled with an inductive power factor to reduce voltages in the distribution networks, voltage stability limit will decline. In addition, the extrusion of conventional power plants in all parts of Germany may cause a further reduction of voltage stability limit as investigations have shown that critical contingencies may be outages of power plants. Thus, this research project has shown the necessity of taking into account voltage stability in system planning. The developed method adds a valuable technique to foresee problems that possibly could occur within the next years.
Publications
- Einfluss von Konventionellen Kraftwerken auf die Spannungsstabilität im Übertragungsnetz unter Berücksichtigung Dezentraler Erzeugung. 13. Symposium Energieinnovation Graz, Austria, 12.-14.2.2014
Dierkes, S.; van Leeuwen, T.; Verheggen, L.; Moser, A.
- Impact of Distributed Reactive Power Control of Renewable Energy Sources in Smart Grids on Voltage Stability of the Power System. IEEE-Electric Power Quality and Supply Reliability Conference (PQ), Rakvere, Estonia, 11.06.-13.06.2014
Dierkes, S.; Bennewitz, F.; Verheggen, L.; Maercks, M; Moser, A.
(See online at https://doi.org/10.1109/PQ.2014.6866795) - Impact of Shunt Compensation on Voltage Stability of Power Systems with a Significant Share of Renewable Energies. CIGRE Conference on innovation for secure and efficient transmission grids, Brussels, Belgium, 12.03.-14.03.2014
Dierkes, S.; van Leeuwen, T.; Moser, A.
