title: Flexible control and optimisation of multi-energy systems
Creators: name: Min, Liang
Publisher: name: University of Glasgow
Year: 2024

description: With the deterioration of the environment and the increasing severity of the energy crisis, the UK government sets the Net Zero 2050 plan. Under this context, the traditional power distribution networks, struggling to adapt to the demands of local renewable energy generation (REG), low-carbon technology, and energy storage, are transforming to active distribution networks (ADNs) with soft open points (SOPs) as a flexible control device for enhanced operational efficiency. Meanwhile, to overcome the limitations of a single energy vector, the multi-energy system (MES), which can utilise the complementary advantages of different energy vectors, becomes a promising solution, especially in facilitating the integration of REGs. As the natural gas network has a mature infrastructure across the UK and the technologies of gas-fired units (GFU) and power-to-gas (P2G) can contribute to the constitution of the energy loop between electricity and gas, the electricity-gas MES become a hot research area. Selecting the electricity-gas MES as the key solution, this PhD research investigates the impact of SOPs on improving the operation of ADNs and explores the role of electricity-gas MES in facilitating the integration of REGs.

For the SOP, the technology is advanced at the converter level, focusing on topology, control, and strategy to improve the operational efficiency of ADNs. The three-phase four-wire (3P4W) back-to-back (B2B) converter is investigated as the new topology of SOPs. Based on the new topology, a new control scheme and the operational strategy are developed. The simulation shows that the 3P4W-B2B converter based ASP-SOP can achieve load balancing and phase imbalance in the unbalanced ADNs.

For the ADN, an optimal operation strategy based on developed ASP-SOPs is proposed to enhance the performance of unbalanced ADNs. The effects of different types of ASP-SOPs is compared. For the first time, in the SOP-based optimisation of ADN, the symmetrical semidefinite programming (SDP) is applied to solve the three-phase optimal power flow problem. The case study demonstrates that the proposed method can achieve a power loss reduction of up to 49.83% and an imbalance reduction of up to 77.68%.

For the MES, encompassing both ADNs and natural gas networks, a comprehensive operational coordination optimisation approach is designed to not only minimise the operational costs, the curtailment of REGs and carbon emissions but also enable simultaneous analysis of both energy vectors’ networks. Additionally, a graph-based model is developed for directly solving the nonlinear optimisation problems in stochastic MES, considering the uncertainties associated with variable REG. The results of case studies indicate that the proposed optimisation method for MESs can reduce the total operational cost by 21.81%, the overall carbon emissions by 33.95% and the curtailment of wind power generations by 94.41%. Furthermore, the implementation of ASP-SOP can significantly mitigate the voltage imbalance condition in three-phase power systems, improving it by up to 36.82%.