Sample page The facts are real. The words are stand-ins — yours go in their place.
Xiaoxiao Liu
A question that would not go away, a method that had to be built twice, and the hour in which all of it is defended in public.
“Towards Coordinated Control and Protection: Interaction Analysis Between MMC-HVDC Control and AC System Protection”
Three questions
Why this topic?
It began with something that bothered me and would not leave me alone. The field had an answer already, and I did not believe it.
What surprised you?
How often the interesting result was the one I was not looking for, and how long it took me to stop treating it as noise.
What happens after the defense?
Sleep, first. Then finding out whether what I learned survives outside the university.
In their words“At the start I thought I knew the answer. By the third year I knew I had not understood the question.”
About the thesis
Modern power systems increasingly rely on power-electronic converters to connect renewable energy sources and high-voltage direct-current links. Unlike traditional synchronous generators, these converters do not respond to electrical faults mainly according to their physical characteristics. Instead, their behaviour is largely determined by software-based control systems. This creates new challenges for protection systems, which must quickly detect and isolate faults to prevent equipment damage and wider disturbances. This thesis studies how the control of Modular Multilevel Converters affects the protection of alternating-current networks, with particular attention to distance protection. Both grid-following and grid-forming converter controls are examined under different types of faults. Detailed computer models are used to investigate how converter controls determine the magnitude, phase and sequence components of the injected fault current. A global sensitivity analysis is then applied to identify which control functions and parameters have the greatest influence on fault behaviour and protection performance.
Selected work
Listed from the KU Leuven agenda.