HVDC grid protection based on fault blocking converters

Ruffing, Philipp Frederic; Schnettler, Armin (Thesis advisor); Blasco-Gimenez, Ramon (Thesis advisor)

1. Auflage. - Aachen : Verlagshaus Mainz GmbH (2020)
Book, Dissertation / PhD Thesis

In: Aachener Beiträge zur Hochspannungstechnik
Page(s)/Article-Nr.: 1 Online-Ressource (vii, 149 Seiten) : Illustrationen, Diagramme

Dissertation, RWTH Aachen University, 2020


Multi-terminal HVDC systems are envisioned as a technically and economically promising solution for the large-scale integration of renewable energy sources into power systems. To limit the impact of contingencies in HVDC networks, which might transmit several gigawatts of electric power, on surrounding AC transmission systems, DC faults must be separated quickly and reliably from the remaining part of the system. Several strategies have been proposed to enable the fast separation of faulted DC lines, either based on fast DC circuit breakers or fault-blocking converters, like full-bridge Modular Multilevel Converters. Due to their high degree of controllability even during fault situations, HVDC networks based on fault-blocking converters enable a quick de-energisation of the DC system and hence allow the separation and isolation of a faulted line under near-zero current and voltage conditions. Consequently, such protection systems allow the application of fault separation devices with reduced current breaking requirements compared to full-size DC circuit breakers. This work evaluates the potential and improves the performance of MTDC protection systems based on fault-blocking converters. To enhance the speed of the fault separation process and reduce the requirements on the switchgear during current interruption, a DC fault control method is developed, which enables the dynamic adjustment of the DC terminal currents and voltages as well as the currents flowing into the faulted line. Thereby, the protection system allows the application of fault separation units with low or even no DC current interruption capabilities while enabling a fast fault separation. To facilitate a quick recovery of the DC grid voltage and its power flow, restoration methods for monopolar and bipolar HVDC networks are examined and refined. Based on the definition of functional requirements, including requirements on interoperability and extensibility, as well as quantifiable performance indicators, the entire process from fault detection to system recovery is assessed in the relevant network and circuit configurations. A qualitative comparison with protection systems based on fast DC circuit breakers located at every line end of an HVDC network indicates that the investigated protection system can be a competitive solution depending on the network’s size and the requirements of the surrounding AC systems. Finally, the thesis gives first results on the application of protection strategies based on fault-blocking converters in extended HVDC grids.