Guest Editorial: Recent trends of power flow control in power system networks

Nowadays, the power system networks (PSNs) are extensively interrelated, which includes connection within utilities, which further extends to inter-utility connections and then moves to the inter-regional and finally the international connections. This needs to be done in order to reduce the electricity cost, and to improve the power supply reliability. These inter-connections empower taking benefit of the load diversity, source diversity, and price of fuel to feed electrical energy to the loads at low cost with required reliability. Much research has been executed on contemporary trends for power flow control (PFC) in between and within PSNs. This Special Issue aims to explore emerging technologies, modelling studies, and advanced design on recent technologies for power flow control in between and within PSNs. The call for the Special Issue has 10 sections, that is, test systems for analysis and simulation of PFC in PSNs, PFC in grid operation and management, HVDC systems for PFC of inter-connected power systems, FACTS devices-based PFC, optimal PFC, HVDC integration within ac grids, flexible asynchronous ac link (FASAL) system, variable frequency transformer (VFT), PFC for congestion management and in the electricity market, impacts of distributed generation, storages and new loads (e.g. electric vehicle) on transmission and distribution system PFC. In this Special Issue, the guest editors have acknowledged a total of 31 papers. Among these 31 papers, two papers have been withdrawn by the authors, four papers have been immediately rejected with referral and one paper has been immediately rejected (unsuitable for referral). The remaining 24 papers we sent for peer review. Among these 24 papers which were sent for review, 13 papers have been accepted, one paper is under major revision, two papers have been rejected (unsuitable for referral), and eight papers have been rejected with the referral. The papers rejected were not meeting the standards of the journal. Thus, the overall submissions were of good quality, which results in the success of this Special Issue. The accepted or under consideration papers are further divided into four categories, that is, power flow controlling devices, improved utilization of existing AC transmission networks, PFC in distribution networks, and PFC in microgrids. Jin et al. [1] propose a transformer type dc power flow controller (DCPFC) based on stacks composed of sub-modules. The converter can perform dc power flow control independently on point-to-point as well as multi-terminal connections, which can be applied to high-voltage or medium-voltage DC grids. Aihong et al. [2] develop the third harmonic network of the power system with a unified distributed power flow controller (UDPFC). First, the influence of the third harmonic current on the third harmonic voltage of the transformer neutral point and the output efficiency of the shunt-side single-phase converter is analyzed and then the range of the third harmonic current is determined. The results show that the proposed method for solving the third harmonic current range can ensure the safety of system operation and enhance the efficiency of UDPFC device operation. Su et al. [3] propose a TrendRank algorithm to identify critical nodes in power grids to ensure the stable operation of power systems. When higher utilization of AC networks is achieved by, for example, power flow control methods, then better vulnerability analysis of critical nodes in the grid is necessary. For this reason, the authors of this paper use data, such as the connection between each node, the power flow between each node of the grid, and the economic dispatch of the information network, to identify the key nodes of the grid very effectively. Asija et al. [4] develop a DTCR-based algorithm for sizing and optimal location of DESS minimizing multi-objective function for congestion management. The suggested algorithm is evaluated on the IEEE-30-bus system. The results show that the DE-PSO-based hybrid optimization technique works good in managing the congestion, while an individual optimization technique like PSO and DE infiltrates resources to a substantial extent to oversee the identical level of congestion. The implemented optimization technique optimally utilizes the resources and saves 27% of BESS (approximate), which can take part on the next day for congestion management. Ranjbar [5] proposes an online protective scheme for estimating critical inter-area angle (CIA) for controlling the inter-area oscillations (IAOs) based on evaluating the rate of changes of the IAOs’ rotor angles as an adaptive tripping index (ATI). For this purpose, by using wide area measuring system (WAMS) data, the synchronous generators (SGs) oscillatory signals Δδ and Δω are measured based on evaluating the signal's correlation coefficients, coherent groups, and corresponding oscillating areas are provided. The effectiveness of the proposed ATI approach is evaluated on the IEEE-39 assessment system which presents positive effects of controlling IAOs through different oscillatory patterns. Lindner et al. [6] integrate grid-scale battery energy storage systems (BESS) in a combined preventive and curative congestion management optimization. It analyses the impact of two operational strategies of the German transmission grid. Then, it outlines curative ad-hoc measures to overcome uncertainties during operational planning and real-time operation. The simulation results indicate that BESSs further increase the use of curative measures and reduce congestion management costs. This paper is managed by an independent Editor, which is outside the organizers of this Special Issue. Zhang et al. [7] propose a network partitioning and hierarchical voltage regulation method using holomorphic embedding method-based sensitivity to overcome the challenge of deterioration of voltage quality in distribution networks. This includes a hierarchical voltage regulation framework in which the upper layer minimizes network losses and voltage deviation, and the lower layer exploits the fast controllability of photovoltaic inverters and hybrid distribution transformers, to autonomously regulate the voltage of each partition. Deliri et al. [8] propose a single-source 11-level inverter which is having reduced switches, quintuple times voltage boosting, extendibility, and natural capacitors charge balancing. In order to get a bipolar voltage waveform, the inverter is utilizing two half-bridges. It can feed high, medium, or low power factor type loads. Due to the low-frequency operation, the switching losses are reduced. It utilizes lesser components to get quintuple times voltage gains with a THD of about 6.8% in output voltage and efficiency of more than 90%. Tayyab et al. [9] develop a novel 1-phase 11-level asymmetrical inverter with two dc sources, six bi-directional switches, two capacitors forming the voltage divider circuit, and one four-quadrant switch. It also utilizes a lower components count with respect to the existing topologies, and thus results in reduction in the system size and cost. The asymmetrical 11-level inverter controls the injected apparent (active and reactive) power fed to the grid. For the control of the apparent power, it uses a level-shifted PWM scheme. Here, both steady-state and dynamic results are achieved. The obtained steady-state and dynamic results show the effectiveness of the proposed inverter in distribution networks. Biricik et al. [10] propose a proportional resonant (PR)-based current control technique for grid integrated PEC inverters utilizing Lyapunov filter-based PLL. The proposed control technique results in zero steady-state error in the grid current. It also eliminates the requirement of the control loop for dc capacitor voltages regulation. The proposed technique is so effective that it provides grid current synchronization even under non-ideal grid voltage condition. Isapour et al. [11] purpose the model of a smart island containing several components, that is, smart transportation system (STS), microgrid (MG), and a smart energy hub (SEH). These components exchange energy (multi-carrier) interactively, including water, power, gas, and heat. The optimal distribution of exchange points within the system is addressed, which drastically reduces the total cost of the system. It also shows that STS is much vulnerable to uncertainties due to the irregular road traffic and the variable nature of renewable energy sources (RESs) outputs within MG. Ansari et al. [12] propose a master-slave based synch vulnerability-resistant control technique for islanded ac microgrid (MG). Here, many BSS-interfaced GSIs are used to perform as master units which form and support many RES-interfaced GFIs. The authors have used a droop control scheme as a main controller for BSS-interfaced GSIs, to absorb excess power from the grid and deliver power to the grid during shortage. The secondary controller is also used which not only provides restoration of voltage and frequency but also safeguards the GFIs synchronization failure because of the master-side communication failures and unhealthy master units. At the same time, it guarantees a stable operation of the MG, maximum utilization of DERs, and exact power-sharing. All the papers selected for this Special Issue show the current trends of power flow control (PFC) in power system networks. The major areas included are power flow controlling devices, improved utilization of existing AC transmission networks, PFC in distribution networks, and PFC in the microgrid. The power flow controlling devices include a DC power flow controller and a unified distributed power flow controller. For improved utilization of existing AC transmission networks, a dynamic thermal rating system to enhance the reliability of the power system, a trend rank algorithm to identify critical nodes and to ensure stable operation of power systems, DE-PSO and TCR-based algorithm for optimal location and sizing of DESS, online protective scheme of estimating critical inter-area angle for controlling the inter-area oscillations and grid integrated battery energy storage systems in a combined preventive and curative congestion management optimization are presented. Under power flow control in distribution networks, a network partitioning and hierarchical voltage regulation method using a holomorphic embedding method, a single-source 11-level inverter improving power quality, a novel single-phase asymmetrical 11-level inverter for controlling the apparent power and a proportional-resonant-based current control strategy for grid-connected PEC inverter with Lyapunov filter-based PLL have been included. For power flow control in the microgrid, a smart island containing several components, a master-slave organized synch vulnerability resistant control strategy for islanded AC microgrid, and the design of an Energy Management System for a microgrid with the grid system has been considered. First, we wish to express our thanks to Prof. Innocent Kamwa, Prof. Christian Rehtanz, and Prof. Federico Milano, Editors-in-Chief of IET Generation, Transmission & Distribution for accepting our Special Issue proposal and for their support throughout this venture. Also, we wish to express our gratitude to all the contributors who submitted novel ideas and scientific results in the Special Issue. We are heartily thankful to the anonymous reviewers who have devoted their valuable time from their busy schedules and suggested the comments in upgrading the quality of manuscripts and helping us in selecting good manuscripts for the Special Issue. Farhad Ilahi Bakhsh (Senior Member, IEEE) received a B.Tech degree in Electrical Engineering and a M.Tech. degree in Power Systems & Drives from Aligarh Muslim University (AMU), Aligarh, India, in 2010 and 2012, respectively. Then he pursued a Ph.D. degree from the Indian Institute of Technology Roorkee, India, in 2017. During his Ph.D. he developed a new method for grid integration for wind energy generation systems which has been recognized worldwide. He served as an Assistant Professor in the Department of Electrical & Renewable Energy Engineering, School of Engineering & Technology, Baba Ghulam Shah Badshah University, Rajouri, J & K, India. He developed an automatic solar tracking system which has been appreciated by IEEE India Council, Centre for Embedded Product Design, Centre for Electronics Design and Technology, Netaji Subhas Institute of Technology in association with IEEE Delhi Section & IEEE CAS, Bangalore Chapter. Currently, he is serving as an Assistant Professor in the Department of Electrical Engineering, National Institute of Technology Srinagar, Jammu & Kashmir, India. He is the founder and Counselor of the IEEE Student Branch, at NIT Srinagar. Recently, he won the ‘10 for 10 Typhoon HIL Award’ from Switzerland, Europe. He delivered several Keynote talks, Invited talks, and Expert Lectures at the National and International levels in conferences, workshops, STC, etc. He has more than 50 published papers in internationally reputed journals, international and nationally reputed conferences. Many times, he got the best paper awards at international conferences. Moreover, he has Indian and Australian-granted patents on his credit. He is the Associate Editor of Distributed Generation & Alternative Energy Journal; Lead Guest Editor of IET Generation, Transmission and Distribution Journal; Lead Guest Editor of IET Power Electronics Journal; Guest Editor of IET Renewable Power Generation Journal; Guest Editor of Renewable Energy Focus, Elsevier; and Guest Editor in Recent Advances in Electrical & Electronic Engineering. His research area of interest includes Performance Analysis and new applications of Variable Frequency Transformer, Application of Power Electronics and Drives in Renewable Energy Systems (Solar and Wind), Multilevel Converters, Alternate Energy Vehicles (Electric/Hybrid), and Multi-phase Drives. Sanjeevikumar Padmanaban (Member’ 12–Senior Member’15, IEEE) received a Ph.D. degree in Electrical Engineering from the University of Bologna, Bologna, Italy, in 2012. He was an Associate Professor at VIT University from 2012 to 2013. In 2013, he joined the National Institute of Technology, India, as a Faculty Member. In 2014, he was invited as a Visiting Researcher at the Department of Electrical Engineering, Qatar University, Doha, Qatar, funded by the Qatar National Research Foundation (Government of Qatar). He continued his research activities with the Dublin Institute of Technology, Dublin, Ireland, in 2014. Further, he served as an Associate Professor with the Department of Electrical and Electronics Engineering, University of Johannesburg, Johannesburg, South Africa, from 2016 to 2018. From March 2018 to February 2021, he has been an Assistant Professor at the Department of Energy Technology, Aalborg University, Esbjerg, Denmark. He continued his activities from March 2021 as an Associate Professor with the CTIF Global Capsule (CGC) Laboratory, Department of Business Development and Technology, Aarhus University, Herning, Denmark. Presently, he is a Full Professor in Electrical Power Engineering at the Department of Electrical Engineering, Information Technology, and Cybernetics, University of South-Eastern Norway, Norway. S. Padmanaban has authored over 750 scientific papers and received the Best Paper cum Most Excellence Research Paper Award from IET-SEISCON’13, IET-CEAT’16, IEEE-EECSI’19, IEEE-CENCON’19, and five best paper awards from ETAEERE’16 sponsored Lecture Notes in Electrical Engineering, Springer book. He is a Fellow of the Institution of Engineers, India, the Institution of Electronics and Telecommunication Engineers, India, and the Institution of Engineering and Technology, UK. He received a lifetime achievement award from Marquis Who's Who—USA 2017 for contributing to power electronics and renewable energy research. He is listed among the world's top two scientists (from 2019) by Stanford University USA. He is an Editor/Associate Editor/Editorial Board for refereed journals, in particular the IEEE SYSTEMS JOURNAL, IEEE Transaction on Industry Applications, IEEE ACCESS, IET Power Electronics, IET Electronics Letters, and Wiley-International Transactions on Electrical Energy Systems, Subject Editorial Board Member—Energy Sources—Energies Journal, MDPI, and the Subject Editor for the IET Renewable Power Generation, IET Generation, Transmission and Distribution, and FACETS Journal (Canada). Khadim Moin Siddiqui is currently working as an Associate Professor and Head of Department in the Department of Electrical Engineering and Department of Electrical & Electronics Engineering at Shri Ramswaroop Memorial College of Engineering and Management, Lucknow. He has received a B.Tech. degree in Electronics Engineering from Azad Institute of Engineering & Technology (AIET), Lucknow (Uttar Pradesh Technical University, Lucknow) in 2007, the M.Tech. degree in Power Electronics & Drives with Honors (Electrical Engineering) from Madan Mohan Malaviya Engineering College, Gorakhpur (Gautam Buddha Technical University, Lucknow) in 2012, and a Ph.D. degree in Electrical Engineering funded by the Technical Education Quality Improvement Program Phase-II from Institute of Engineering & Technology, Lucknow (Dr A. P. J. Abdul Kalam Technical University, Lucknow) in 2017. He has published more than 40 research papers in international journals, 15 papers presented at national as well as at international conferences and published four book chapters. He has received best research paper awards at one national and two international conferences. He has published two books in the field of Electrical Engineering & Technology. He has more than 12 years of experience. He is the editorial board member of an international journal and a reviewer of many reputed journals such as and IEEE Industry International Journal on Electrical Engineering and Global and an reviewer of IEEE International and National He is an of the IEEE Student Branch, Lucknow. He is an and organized many at national as well as international levels such as He has been an IEEE member He has delivered Expert Lectures in the field of power electronics & and in many and in the IEEE He has and part in more than 40 He has the at many international conferences. His research area of interest includes Electrical and of and power transformers, inverters and smart grid, Renewable and Energy & He has been of the March 2021 by the IEEE He is the Guest Editor of Distributed Generation & Alternative Energy Journal and IET Generation, and Distribution (Senior Member, IEEE) received the degree in Electrical Engineering from University, the degree from the University of and Technology, and the Ph.D. degree in Electrical Engineering from the in 2018. He is currently a Assistant at the Department of Electronic & Electrical Engineering Institute for Systems University of UK. He has published more than research papers at international conferences and journals and two His research include electrical and electrical systems, optimization methods, transportation and renewable energy systems. He has been the Lead of the IEEE Power and Energy in 2018. He is also an Editor of Energy System and Power Engineering journal. received the and Ph.D. in Electrical Engineering from the Department of Electrical Engineering, University of Technology, in 2012, and respectively. From to he was a Visiting Ph.D. with the Department of Energy Technology, Aalborg University, Denmark. He was a Research Fellow at Aalborg University from 2017 to In he was a Visiting Researcher with Power at University of Technology, The He is currently an Assistant Professor in electrical power at Aalborg His research include the and of power power systems, and renewable received his degree in Electrical Engineering in and his Ph.D. degree in 2012 from the University, Currently, he works as a at the Institute of Energy Systems, Energy and Energy at 2012 he has many national and international research as a His of interest are for electricity grids, curative congestion management and between and uses of was a Professor of Electrical and Engineering at the University of and Technology, from to He is currently the Energy Professor of Power Engineering and a Professor of Electrical and Engineering and Engineering with University, USA. He is also the and of the Power and Systems at He is an Professor with the School of Engineering, University of South He is the top of the College of Engineering and at University, to the Expert and was the Most Researcher of University by in and He has been in over sponsored over He has authored over refereed His are about times with an of His current research include the and of advanced for smart grid including and power system and and is a Fellow of the Institution of Engineering and Technology and the South Institute of Electrical He received the IET Generation, Transmission and Distribution Award for the best research paper published in for the paper for of a Power System with Vehicles in 2012. He in the and of many conferences, including the of the Power System in 2013, and the and of the IEEE of in He is the of the IEEE Power & Energy on Systems and the and of the IEEE on He has served as an Editor of several IEEE and

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