New phase-changing soft open point and impacts on optimising unbalanced power distribution networks

Three-phase unbalanced conditions in distribution networks are conventionally caused by load imbalance, asymmetrical fault conditions of transformers and impedances of three phases. The uneven integration of single-phase distributed generation (DG) worsens the imbalance situation. These unbalanced conditions result in financial losses, inefficient utilisation of assets and security risks to the network infrastructure. In this study, a phase-changing soft open point (PC-SOP) is proposed as a new way of connecting soft open points (SOPs) to balance the power flows among three phases by controlling active power and reactive power. Then an operational strategy based on PC-SOPs is presented for three-phase four-wire unbalanced systems. By optimising the regulation of SOPs, optimal energy storage systems dispatch and DG curtailment, the proposed strategy can reduce power losses and three-phase imbalance. Second-order cone programming (SOCP) relaxation is utilised to convert the original non-convex and non-linear model into an SOCP model which can be solved efficiently by commercial solvers. Case studies are conducted on a modified IEEE 34-node three-phase four-wire system and the IEEE 123-node test feeder to verify the effectiveness, efficiency and scalability of the proposed PC-SOP concept and its operational strategy

Determination of local voltage control strategy of distributed generators in active distribution networks based on kriging metamodel

The increasing penetration of uncontrollable distributed generators (NDGs) exacerbates the risk of voltage violations in active distribution networks (ADNs). It is difficult for a centralized control strategy to meet the requirements of fast voltage and reactive power control because of the heavy computational and communication burdens. Local voltage control based on real-time measurements can respond quickly to the frequent fluctuations of distributed generators (DGs). In this paper, a local voltage control strategy of DGs with reactive power optimization based on a kriging metamodel is proposed. First, to build the metamodel for local voltage control, the steps for determining the input variables are presented in detail, and the effects of different variables on the accuracy of the metamodel are analyzed. Then, taking minimum network losses and voltage deviations as the objective function, we construct the metamodel for local voltage control based on kriging methods. Finally, operation strategies for DGs are developed by calculating the optimally weighted vector based on real-time measurements, and the operation strategies for DGs will be added into the original sample set to improve the accuracy of the metamodel. The proposed local voltage control strategy based on only the local measurements can quickly respond to the frequent DG fluctuations, reduce the communication burden for large networks and improve the adaptability of local voltage control in ADNs. Case studies under different scenarios on the IEEE 33-node system and the IEEE 123-node system are conducted to verify the effectiveness of the proposed method, and the results show that the proposed method can effectively solve the problems of voltage deviation and voltage fluctuation caused by the high penetration of DGs

Optimal operation of soft open points in active distribution networks under three-phase unbalanced conditions

The asymmetric integration of distributed generators (DGs) exacerbates the three-phase unbalanced condition in distribution systems. The serious unbalanced operation causes inefficient utilization of network assets and security risks in the system. Soft open point (SOP) is a flexible power electronic device which can achieve accurate active and reactive power flow control to balance the power flow among phases. This paper proposes an SOPs-based operation strategy for unbalanced active distribution networks. By regulating the operation of SOPs, the strategy can reduce power losses and simultaneously mitigate the three-phase unbalance of the upper-level grid. Semidefinite programming (SDP) relaxation is advocated to convert the original non-convex, nonlinear optimization model into an SDP formulation, which can be efficiently solved to meet the requirement of rapid adjustment. Case studies are conducted on the modified IEEE 33-node and IEEE 123-node distribution system to verify the effectiveness and efficiency of the proposed strategy

Operational flexibility of active distribution networks: definition, quantified calculation and application

With a high penetration of intermittent distributed generators (DGs), the uncertainties in active distribution networks (ADNs) are exacerbated and further coupled in the networks. It brings enormous challenges on system operation and puts forward a higher requirement for the operational flexibility of ADNs. However, due to the secure constraints and diverse operational requirements, the controllability of controllable resources (CRs) cannot fully facilitate the flexible operation of ADNs. Operational flexibility is seen as a link between diverse operational requirements and flexible adjustment capabilities of CRs, which also represents the ability of the network to deploy its CRs to respond to the change of operation states. Under the framework of operational flexibility, multiple types of operational optimization problems can be reinterpreted, which provides a new perspective for the operation of ADNs. In this paper, the definition and region-based mathematical formulation of operational flexibility for ADNs are proposed firstly. Then the quantified calculation method of operational flexibility is proposed to represent flexibility provision (FP) and flexibility availability (FA). The application of operational flexibility is analyzed from the perspective of diverse operation and improvement of flexibility. Finally, case studies are performed on the modified IEEE 33-node system to show the effectiveness of the proposed method

Soft Open Point in Distribution Networks

The main objective of this article is to present a comprehensive review of soft open point (SOP), an emerging power electronics technology to maximize future distribution networks’ (DNs) resiliency and flexibility as well as increase hosting capacity for distributed energy resources like photovoltaics and electric vehicles. The SOP is currently an active area of research and ongoing development of new control techniques for SOP and optimization algorithm for the optimal use of SOP in DNs produces new techniques until DN operators use it comprehensively in their systems. The motivation for this work is to present the research that has been completed for the SOP and summarize the duties of SOP in DNs according to the literature and propose advanced duties for SOP according to modern standards. Finally, future research directions are mentioned to pave the way for research in the coming years to drive the DNs towards more flexibility and ‘Robust’ from controllability, stability, and protection structure point of view.© 2020 Authors. This work is licensed under a Creative Commons Attribution 4.0 License. For more information, see https://creativecommons.org/licenses/by/4.0/fi=vertaisarvioitu|en=peerReviewed

An overview of soft open points in electricity distribution networks

Soft open points (SOPs) are power electronic devices that are usually placed at normally open points of electricity distribution networks to provide flexible power control to the networks. This paper gives a comprehensive overview of both academic research and industrial practice on SOPs in electricity distribution networks. The topologies of SOPs as multi-functional power electronic devices are identified and compared, which include back-to-back voltage source converters, multi-terminal voltage source converters, unified power flow controllers, and direct AC-to-AC modular multilevel converters. The academic research is reviewed in three aspects, i.e., benefit quantification, control, and optimal siting and sizing of SOPs. The benefit quantification indices are categorized into feeder load balancing, voltage profile improvement, power losses reduction, three-phase balancing and DG hosting capacity enhancement. The control of SOPs is summarized as a three-level control structure, where the system-level and converter-level control are further discussed. For optimal siting and sizing of SOPs, problem formulation and solution methods are analyzed. Besides the academic research, practical industrial projects of SOPs worldwide are also summarized. Finally, opportunities of research and industrial application of SOPs are discussed

A scientometric analysis of the emerging topics in general computer science

Citations have been an acceptable journal performance metric used by many indexing databases for inclusion and discontinuation of journals in their list. Therefore, editorial teams must maintain their journal performance by increasing article citations for continuous content indexing in the databases. With this aim in hand, this study intended to assist the editorial team of the Journal of Information and Communication Technology (JICT) in increasing the performance and impact of the journal. Currently, the journal has suffered from low citation count, which may jeopardise its sustainability. Past studies in library science suggested a positive correlation between keywords and citations. Therefore, keyword and topic analyses could be a solution to address the issue of journal citation. This article described a scientometric analysis of emerging topics in general computer science, the Scopus subject area for which JICT is indexed. This study extracted bibliometric data of the top 10% journals in the subject area to create a dataset of 5,546 articles. The results of the study suggested ten emerging topics in computer science that can be considered by the journal editorial team in selecting articles and a list of highly used keywords in articles published in 2019 and 2020 (as of 15 April 2020). The outcome of this study might be considered by the JICT editorial team and other journals in general computer science that suffer from a similar issue