Analysis of long-term voltage stability in electric power systems under consideration of active distribution networks and novel emergency control systems

The large-scale installation of distributed generating units and high-voltage direct current transmission systems as well as the decreasing number of synchronous generators change dynamics and stability of future electric power systems. Especially in case of unforeseen network conditions and severe contingencies the risk of regional or large-scale blackouts due to long-term voltage instability rises. In such situations, the changing dynamic behaviour of distribution networks plays an important role and needs to be further investigated. The first target of this thesis is thus to provide a modelling and evaluation approach of a combined transmission-distribution network that enables to gain qualitative insights in the behaviour of future electric power systems. Here, a particular focus is to identify how the decomposition of the load and the control of distributed energy resources influence post-fault system dynamics and long-term voltage instability. Nevertheless, even with these changes a both secure and efficient power supply needs to be guaranteed for all network conditions, which requires novel monitoring and emergency control systems against voltage collapse. Therefore, this thesis further aims at developing a distributed agent-based emergency control approach for the reliable identification of an evolving long-term voltage instability and the coordinated activation of available countermeasures.