• Energy Research

AbstractDistributed Generators that use reactive power for voltage control in distribution networks reduce renewable curtailment but can significantly increase network losses, undermining the effectiveness of this control. This paper proposes Voltage Control Loss Factors (VCLFs) as a means of understanding the interactions between reactive power flows, losses and curtailment, focusing on commercial‐scale generators in radial systems. The metric uses a substitution‐based method, whereby a system with voltage control is compared against a counterfactual with no such control. The proposed method studies this metric by coupling numerically precise black‐box simulations with analytic results from a Two‐Bus network representation. The latter provides a physical explanation for the numerical simulation results in terms of power, voltage and impedance parameters, providing clear explainability which is absent in traditional approaches for determining distribution loss factors. The whole solution space of the Two‐Bus system is explored, and VCLFs are calculated for six cases on three unbalanced test networks to illustrate the approach. Relative losses as high as 30% are found in a system with high branch resistance‐reactance ratio and large voltage rise. The results have implications for the design of loss allocation algorithms in distribution networks, and the optimal sizing of power‐electronic interfaced Distributed Generators.

Abstract Increasing demand-side flexibility is important for decarbonising electricity systems with increasing intermittent and variable renewable energy. Although previous research has identified reduction of carbon emissions from electricity consumption as a driver for households to provide demand-side flexibility, it is not clear yet whether they are willing to provide additional flexibility if the emission reduction takes place locally. This study conducted an online factorial survey across the UK to investigate the determinants of domestic consumers' willingness to participate in time-of-use and direct load control of electric vehicle charging and heat pump heating programs. The results show that consumers generally prefer the static time-of-use tariffs (programs) to more flexible, controlled charging/heating programs (e.g. vehicle-to-grid charging), but savings on electricity bills, the percentage of reduced carbon emissions, and localisation of emission reduction (i.e. contributing to local emission targets) can significantly motivate participation in demand-side flexibility programs. Keeping other variables constant, localisation of emission reduction can increase the likelihood of program acceptance by over 11\%. Socio-demographic variables (e.g age), energy-related behaviours (e.g. intention to buy an electric vehicle or a heat pump, the current expenditure in electricity), consumers' trust in electricity service suppliers, their concerns over data privacy, and attitudes towards climate change and local carbon targets also influence household willingness to provide demand-side flexibility.

Digital Twins promise to deliver a step-change in distribution system operations and planning, but there are few real-world examples that explore the challenges of combining imperfect model and measurement data, and then use these as the basis for subsequent analysis. In this work we propose a Digital Twin framework for electrical distribution systems and implement that framework on the Smart Energy Network Demonstrator microgrid in the UK. The data and software implementation are made available open-source, and consist of a network model, power meter measurements, and unbalanced power flow-based algorithms. Measurement and network uncertainties are shown to have a substantial impact on the quality of Digital Twin outputs. The potential benefits of a dynamic export limit and voltage control are estimated using the Digital Twin, using simulated measurements to address data quality challenges, with results showing curtailment for an exemplar day could be reduced by 56%. Power meter data and a network model are shown to be necessary for developing algorithms that enable decision-making that is robust to real-world uncertainties, with possibilities and challenges of Digital Twin development clearly demonstrated.

© 2023 The AuthorsSoft Open Points (SOPs) are power electronic-based devices which can replace Normally Open Points (NOPs) in distribution networks. They can improve network performance by enabling controllable power transfer between adjacent feeders. This flexible meshing can provide a wide range of services, including loss reduction, reduced renewables curtailment, improved reliability, reinforcement deferral, or enabling flexibility services. This paper proposes a novel framework, based on the Cost–Benefit Analysis methodology, to quantify and compare the cost-effectiveness of SOPs for providing each of these five value streams. The framework includes the development of mathematical models that encapsulate the key variables that drive competitive SOP use cases, as well as providing detailed analysis to determine quantitative estimates for each of the parameters. Results suggest that, whilst all services could be cost-effective, that reinforcement deferral and reduced DG curtailment are most likely to find wide usage. It is also suggested that the fast response time of SOPs as compared to conventional NOPs is unlikely to be a viable value proposition for improving reliability via conventional loss of load metrics such as energy not supplied. A detailed case study demonstrates that in marginal cases, where a SOP has a similar system net benefit compared to Business-as-Usual, that all services need to be considered rather than just single value streams in isolation. It is concluded from the research that there are multiple potential competitive applications for SOPs in future distribution networks.

This paper studies the distribution network impacts of frequency containment services derived from domestic-scale devices. Risk metrics considering the likelihood and severity of violations are proposed, given uncertainty in the location of these devices. A novel linearization approach is proposed to enable detailed simulations of large-scale networks, capturing MV–LV coupling in European-style networks of over 100 000 nodes. The approach combines a novel factorization of the power flow Jacobian matrix and an efficient linearization update step. The first of these innovations improves the scalability and practicality of the linearization, reducing the memory and computational requirements by as much as twenty times, whilst the latter reduces the median linearization error by at least 50% in all networks studied. It is demonstrated that rapid voltage change (RVC) and overvoltage constraints could limit the uptake of these devices to just a fraction of one percent of customers if the response is not managed. Sensitivity analysis demonstrates that both the likelihood and severity of constraint violations increases rapidly with the size of the devices used for frequency response.

Distribution systems will require new cost-effective solutions to provide network capacity and increased flexibility to accommodate Low Carbon Technologies. To address this need, we propose the Hybrid Multi-Terminal Soft Open Point (Hybrid MT-SOP) to efficiently provide distribution system interconnection capacity. Each leg of the Hybrid MT-SOP has an AC/DC converter connected in series with a bank of AC switches (Feeder Selector Switches) to allow the converter to connect to any of the feeders at a node. Asymmetric converter sizing is shown to increase feasible power transfers by up to 50% in the three-terminal case, whilst a conic mixed-integer program is formulated to optimally select the device configuration and power transfers. A case study shows the Hybrid MT-SOP increasing utilization of the converters by more than one third, with a 13% increase in system loss reduction as compared to an equally-sized MT-SOP. Preprint submitted to Electric Power Systems Research (Power Systems Computation Conference 2022)

The feasible set of real powers that can be transferred by a three-terminal Soft Open Point (SOP) can be increased by selecting non-uniform power ratings for each of the three ac/dc legs of the SOP, then connecting a multi-terminal switch (multiplexer) to the ac side of each of those converters to facilitate reconfiguration. This paper generalizes this concept, considering the real and reactive power that n multiplexed ac/dc converters can transfer at an m-feeder bus. The performance of the device is studied numerically for a number of ac/dc sizing strategies through the volume of the feasible set of power transfers (the `capability chart volume', CCV) and distribution system loss reduction benefits (as an exemplar network service). Upper bounds on device performance are defined by considering the performance of a novel, idealised SOP consisting of a continuum of infinitesimal reconfigurable converters. Results demonstrate that the CCV can be more than doubled, with 99% of the relative performance improvement of the idealised converter achieved with designs consisting of as few as four converters. SOP equipment costs reductions of 24% are reported, with it concluded that reconfigurable, judiciously sized ac/dc legs can yield flexible and lower cost SOPs than conventional, hard-wired approaches. Article accepted in IEEE Transactions on Smart Grid