Towards Coordinated Control and Protection: Interaction Analysis Between MMC-HVDC Control and AC System Protection

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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.