Modelling and Optimisation for a Coordinated Interconnected Multi-Terminal DC Transmission Infrastructure for Integration of Offshore Wind Energy

The modern power system is undergoing significant modifications as a result of the integration of variable renewable energy system, particularly offshore wind farms. These modifications have increased the complexity of power grid operations, especially in terms of maintaining a balance between variable generation and demand. Consequently, operational planning has become notably more challenging, requiring greater flexibility (i.e., the ability to provide control and load-following throughout a wider operating range) to meet demands, whilst maintaining the security and reliability of the power system. This thesis presents a reinforcement model for transmission systems, designed to enhance the operational planning of hybrid AC/DC networks integrated with offshore wind farms, with a particular emphasis on the MT-HVDC link, through the utilisation of Voltage Source Converter (VSC) technology. A mathematical model for hybrid AC/DC networks is developed based on the Flexible Universal Branch Model (FUBM) to provide functionalities, which offer flexibility in both short-term and long-term operational planning, specifically addressing the optimisation problems of Optimal Power Flow (OPF) and Security Constrained OPF (SCOPF). This mathematical model has been tested using control techniques (i.e., conventional control and droop control) in the VSC in-model (one model in the FUBM) incorporated with the Remedial Action Scheme (RAS), known as RAS-FUBM (i.e., RAS-FUBM conventional control and RAS-FUBM droop control), whilst considering a range of scenarios (e.g., worst-case scenarios, multi-period scenarios, and multi-objective scenarios). The results clearly show that the model demonstrates greater flexibility and reliability, as well as mitigates the contingencies (following the standard N-1 rule) and congestion within the MT-HVDC link. These results provide a benchmark for modern operational planning and assist Transmission System Operators (TSOs) in making optimal decisions, thereby ensuring both reliability and economic feasibility in power system operation.