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

Abstract

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.