Modelling the impact of flexible AC transmission systems on the operation of electrical transmission grids

Mitigating climate change is one of the greatest challenges of our time. In order to reach the Paris agreement of keeping global warning well below 2°C, massive changes in the German and European energy system are indispensable. One of the measures is the decarbonization of the electricity generation sector, resulting in the decommissioning of conventional power plants like coal and lignite and a massive expansion of renewable energies capacities, especially onshore and offshore wind and photovoltaic. Together with the prognosed overall increasing electricity demand, the fluctuating generation from renewables and the missing, easily controllable generation from conventional power plants represent a great challenge for the German and European transmission grid today and even more in the upcoming years and decades, since the balance between generation and demand must be maintained at all times without violating voltage, frequency or thermal limits. Grid expansion is necessary and already in planning, but the process of building new transmission lines is costly and time consuming. Another supplementary approach is grid reinforcement, which includes measures that help in utilizing the existing transmission lines to their full potential. ... mehrOne of these measures is the use of flexible AC transmission systems (FACTS). This group of electrotechnical devices is able to provide reactive power and thus secure voltage stability as well as to control power flows in the transmission system. An extensive application of FACTS can be used to prevent and resolve congestions in the transmission grid and thus reduce redispatch volumes and costs, renewables curtailment and load shedding. To further investigate the technical and economic potential of FACTS in the future energy system, we provide technically detailed models for different types of FACTS, which are then integrated into an AC optimal power flow model. We check for plausibility by using a standard testcase, where the theoretical potential of FACTS in congestion management is already indicated. We then present the first results of a case-study, where we applied the model on the German energy system including the transmission grid, and discuss the findings and further research options and goals.