Protection System and HVDC Converter Control Interaction in Renewable Energy Dominated Power Systems

The amount of renewable energy generation in the power system is increasing rapidly, displacing fossil-fuel based generation sources. Although bringing significant societal benefits, this transformation is causes challenges for the safe operation of the electrical power system. To transport energy from the renewables to the end-users, new types of transmission links, such as the high-voltage dc (HVDC) links used between Belgium and UK, are necessary. These links are interfaced to the existing power system through power-electronic converters (so-called modular multilevel converters) which require a plethora of control loops that act on a very small timescale. These controls pose challenges for the existing means of protecting the power system against short-circuit faults, as the protections are designed for the slow fault characteristics of synchronous machines of the fossil-fuel based power plants. Recent research in this field focused on power system aspects, taking a given converter control structure for granted or ignoring inner converter controls. The interactions between the power system protections and HVDC converter control loops, and the numerous possibilities to implement these controls, are at present not well characterized. Therefore, this project aims at (i) an in-depth characterization of the interactions between (both traditional and state-of-the-art) HVDC converter control and existing system protections and (ii) designing the converter controls to improve these interactions. The project will result in new converter models, including all relevant controls for protection interaction studies, with improved controls for protection. To ensure validity of the obtained results, the project will make extensive use of hardware experiments.