Benefit analysis of using soft DC links in medium voltage distribution networks

Soft DC Links are power electronic converters enabling the control of power flow between distribution feeders or networks. This thesis considers the use of Soft DC Links in Medium Voltage (MV) distribution networks to improve network operation while facilitating the integration of distributed generators (DGs). Soft DC Links include Soft Open Points (SOPs) and Medium Voltage Direct Current (MVDC) links. An SOP can be installed to replace mechanical switchgear in a network, providing controllable active power exchange between connected feeders, as well as reactive power compensation at each interface terminal. The deployment of an MVDC link enables power and voltage controls over a wider area, and facilitates the effective use of available capacity between adjacent networks. The benefits of using SOP and MVDC link in MV distribution networks were investigated. A multi-objective optimisation framework was proposed to quantify the operational benefits of a distribution network with an SOP. An optimisation method integrating both global and local search techniques was developed to determine the set-points of an SOP. It was found that an SOP can improve network operation along multiple criteria and facilitate the integration capacity of DGs. A Grid Transformer-based control method of an MVDC link was proposed, which requires only measurements at the grid transformers to determine the operation of an MVDC link. Control strategies considering different objectives were developed. The proposed control method is used in the ANGLE-DC project, which aims to trial the first MVDC link in Europe by converting an existing AC circuit to DC operation. It was found that an MVDC link can significantly increase the network hosting capacity for DG connections while reducing network losses compared to an AC line. An impact quantification of Soft DC Links was carried out on statistically-similar distribution networks, which refer to a set of networks with similar but different topological and electrical properties. A model was developed to determine the optimal allocation of Soft DC Links. It was found that a Soft DC Link can reduce the network annual cost under a wide range of DG penetration conditions. The statistical analysis provides distribution network planners with more robust decisions on the implementation of Soft DC Links

Impacts of a medium voltage direct current link on the performance of electrical distribution networks

With an increasing number of distributed generators (DGs) integrated into distribution networks, operational problems such as excessive power losses, voltage violations and thermal overloads have occurred. Medium Voltage Direct Current (MVDC) technology represents a candidate solution to address these problems as well as to unlock the capacity of existing electrical network assets. In this paper, the capability of using an MVDC link to improve the performance of a distribution network, i.e. reducing power losses and increasing the hosting capacity for DG connections was investigated. A grid transformer (GT)-based control method was developed, in which the real-time data of the active power flow at GTs was used to specify the set-points of an MVDC link. The control strategies considered multiple objectives, i.e. power loss reduction, feeder load balancing, voltage profile improvement, and trade-off options among them. The response curves of these control strategies were developed through offline studies, where a multi-objective Particle Swarm Optimization (MOPSO) method was used. Case studies on a real distribution network were conducted to analyze the impacts of the MVDC link. The performances of the network were evaluated and compared between the proposed control strategies, using real demand and generation profiles. Results revealed that, for an MV distribution network, it might be beneficial to switch between different control strategies with the variations in demand and generation conditions. Results also showed that, regardless of the control strategy used, the MVDC link can significantly increase the network hosting capacity (up to 15%) for DGs, and reduce about 50% of power losses compared to a conventional alternative current (AC) line for the test network

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

Power quality and electromagnetic compatibility: special report, session 2

The scope of Session 2 (S2) has been defined as follows by the Session Advisory Group and the Technical Committee: Power Quality (PQ), with the more general concept of electromagnetic compatibility (EMC) and with some related safety problems in electricity distribution systems. Special focus is put on voltage continuity (supply reliability, problem of outages) and voltage quality (voltage level, flicker, unbalance, harmonics). This session will also look at electromagnetic compatibility (mains frequency to 150 kHz), electromagnetic interferences and electric and magnetic fields issues. Also addressed in this session are electrical safety and immunity concerns (lightning issues, step, touch and transferred voltages). The aim of this special report is to present a synthesis of the present concerns in PQ&EMC, based on all selected papers of session 2 and related papers from other sessions, (152 papers in total). The report is divided in the following 4 blocks: Block 1: Electric and Magnetic Fields, EMC, Earthing systems Block 2: Harmonics Block 3: Voltage Variation Block 4: Power Quality Monitoring Two Round Tables will be organised: - Power quality and EMC in the Future Grid (CIGRE/CIRED WG C4.24, RT 13) - Reliability Benchmarking - why we should do it? What should be done in future? (RT 15

Port choice by intra-regional container service operators : an application of decision-making techniques to liner services between Malaysian and other Asian ports

Intra-regional container service operators are challenged to design regular and reliable liner services connecting regional ports at the lowest cost and shortest transit time while considering customer demand. This paper focuses on the selection of ports of call in regular intra-regional container services, an under-researched part of the container shipping market. A combination of decision-making techniques (i.e. Analytical Hierarchy Process, fuzzy link-based and Evidential Reasoning) are presented to assist intra-regional container service operators in selecting ports of call. The proposed methodology is empirically applied to container services between Malaysian and other nearby Asian ports. While Port Klang is the main gateway to Malaysia, the results show that other Malaysian ports should play a more prominent role in accommodating intra-Asian container services. This research can assist maritime stakeholders in evaluating intra-regional port-to-port liner service configurations. Furthermore, the novel mix of decision-making techniques complements and enriches existing academic literature on port choice and liner service configuration

Integration of Large PV Power Plants and Batteries in the Electric Power System

The declining cost of renewables, the need for cleaner sources of energy, and environmental protection policies have led to the growing penetration of inverter-based resources such as solar photovoltaics (PV), wind, and battery energy storage systems (BESS) into the electric power system. The intermittent nature of these resources poses multiple challenges to the power grid and substantial changes in the conventional generation and electrical power delivery practices will be required to accommodate the large penetration of these renewable power plants. The impact of large solar PV penetration on both generation and transmission systems, and the use of BESS to mitigate some of the challenges due to solar PV penetration has been studied in this dissertation. One of the major challenges in evaluating the impact of inverter-based resources (IBR) such as solar PV systems is developing an equivalent model adequate to represent its operation. This work proposes a detailed solar PV model suitable for analyzing the configurations, design, and operation of multi-MW grid connected PV systems. This model which takes into account the contributions of the power electronics control and operation was used to evaluate the impact of transient changes in solar PV power on an example transmission system. The benefits of a battery system configuration connected to the grid through an independent inverter were analyzed and its operation during transient conditions was also evaluated. After developing a detailed solar PV and BESS modules for analyzing the effect of IBR on transmission systems, an innovative approach for evaluating the impact of solar PV plants on both generation and transmission system based on a practical minute-to-minute economic dispatch model was proposed. The study demonstrates that large solar PV penetration may lead to both over- and under-generation violations, and substantial changes to conventional generation dispatch and unit commitment will be required to accommodate the growing renewable solar PV penetration. The terminal voltage of a battery pack varies based on multiple parameters and cannot be modeled as a constant voltage source for a detailed analysis BESS operation. A novel approach for estimating the equivalent circuit parameters for utility-scale BESS using equipment typically available at the installation site was proposed in this dissertation. This approach can be employed by utilities for monitoring energy storage system operation, ensure safety and avoid lithium-ion battery thermal runaway . The new methods developed, configurations and modules proposed in this dissertation may be directly applicable or extended to a wide range of utility practices for evaluating the impact of renewable resources and estimating the maximum solar PV capacity a service area can accommodate without significant upgrades to existing infrastructures

Optimal operation of soft open points in medium voltage electrical distribution networks with distributed generation

A soft open point (SOP) is a power electronic device, usually using back-to-back voltage source converters (VSCs), installed at a previously normally open point of a distribution network. Due to its flexible and accurate control of power flows, an SOP is versatile, and increasingly being considered to mitigate voltage and thermal constraints in medium voltage (MV) networks with high penetrations of distributed generation (DG). A Jacobian matrix - based sensitivity method was used to define the operating region of an SOP when the grids/feeders at the two terminals of the SOP have various load and generation conditions, and the SOP operating region was visualized in a graphical manner. The exact operating set-points were determined by adopting a non-linear optimization considering separately different objectives. The methodology was demonstrated on an 11 kV network, considering three optimization objectives with different DG penetrations and different network observabilities. Results showed that the use of an SOP significantly increases the network’s DG hosting capacity. The objective for voltage profile improvement increased the headroom of the voltage limits by the largest margin, at the expense of increased energy losses. In contrast the objectives to achieve line utilization balancing and energy loss minimization showed the most improvement in circuit utilization and in limiting energy losses. The work helps electricity network operators to visualize an SOP’s operation status, and provides high level decision support, e.g. selecting control schemes and restraining SOP operational boundaries