FRT-Verhalten von umrichtergespeisten Synchronmaschinen beim Netzwiederaufbau

This master thesis investigates conventional hydropower plants, variable-speed pumped storage units with fully converter-fed synchronous machines (CFSM), grid faults, and dynamic grid stability in investigations into the robustness of island grids against electrical faults during grid restoration. The integration of the CFSM into grid restoration significantly impacts the grid dynamics, as the existing rotating inertia is reduced and the machine's stability behavior changes. This work therefore aims to analyze the FRT behavior of CFSMs under external electrical faults in order to improve dynamic stability in island grids. The work can be divided into six main chapters. In the introduction chapter, the initial situation, the problem statement, the research question, the objectives, and the methodological approach are explained in more detail. The research question to be clarified, "How does an external three-phase short circuit affect the stability of an island grid with a dominant converter-fed load, and what conclusions can be drawn for the implementation of a real field test?" will be answered within the scope of this work. Chapter 2 covers the theoretical foundations. At the beginning, the individual components of the system are described. Next, the topic of black start capability is discussed in more detail. At the end of this chapter, the various short-circuit processes and dynamic network stability are explained. Chapter 3 deals with modeling, specifically the software used, the existing models, and their adjustments. The investigation of the research question is conducted using a simulation in DIgSILENT PowerFactory. The existing plant models of the conventional hydropower plant and a variable-speed pumped storage unit with a fully converter-fed synchronous machine are integrated. The model is extended with a turbine controller for the CFSM to illustrate the dynamic processes. Chapter 4 comprises the simulation analysis, which can be roughly divided into static calculation and dynamic short-circuit analysis. In the simulation, the maximum and minimum short-circuit currents as well as the voltage dips are determined in the static analysis. In the dynamic analysis, the three-phase short circuit is simulated at various fault locations, and the frequency response as well as the critical clearing time (CCT) are examined to assess stability. Tests with an additional island grid and a load connection are also conducted. Chapter 5 draws conclusions from the simulation for the field test. It shows that the CFSM offers significant advantages regarding the critical fault clearing time, the transient response, and the associated post-fault stability. These findings form the basis for a field test. Chapter 6 of the work concludes with a summary and an outlook.