bluuebunny/crossref_metadata_2025_split huggingface dataset:
Influence of phase‐locked loop aggregation on the dynamic aggregation of wind farm strings with heterogeneous parameters
Authors: Taul Mads Graungaard , Wang Xiongfei , Davari Pooya , Blaabjerg Frede 
Published: February 2021

AbstractOffshore wind farms are cornerstone solutions for enabling large‐scale integration of renewable energy. Due to the large number of wind turbines in a wind farm, each with their individual complex control structure, a detailed time‐domain model for analysis of wind farms is impractical from a computational burden perspective. Accordingly, aggregated models have been presented to reduce the computation time. Despite the high activity in aggregated modelling of wind farms, dynamic aggregation considering heterogeneous converter controllers and filter parameters, including different phase‐locked loop (PLL) parameters have not been discussed previously. To remedy this issue, this study proposes an aggregated structure‐preserving model of a wind farm string where all converters have heterogeneous parameters. The proposed model is verified by simulations against a detailed numerical model of the wind farm string, showing its accuracy in preserving the wind farm string dynamics under a severe grid fault with different short‐circuit ratios and PLL parameters. Through a comparison of four different PLL aggregation methods under the considered case studies, it is found that the PLL aggregation has a negligible influence on the aggregated response and, hence, the particular aggregation method employed is not of great importance.
Coordinated design of delay‐dependent wide‐area damping controllers considering multiple time delays
Authors: Yao Wei , Yan Cai , Liu Xinmiao , Zhang Chuan‐Ke , Jiang Lin , Wen Jinyu 
Published: February 2021

AbstractThis paper investigates coordinated design of multiple wide‐area damping controllers (WADCs) for damping multiple inter‐area oscillations considering communication delays in multiple control loop. Two approaches have been investigated: the sequential approach which uses the stability criteria for single delay and design the WADC independently, and the coordinated approach which employs a less conservative and fast Lyapunov stability criterion for linear system with multiple delays to calculate delay margins simultaneously and coordinately design the multiple WADCs. The sequential approach cannot reveal the interaction among several WADCs loops with multiple delays and may lead to inaccurate delay margins, while the coordinated approach takes into account interactions of delays between different WADC control loops and can result in accurate delay stable region and relationship between delay margins and the WADC gains. Gains of WADCs are determined based on a trade‐off between damping performance and delay margin. Case studies are based on the modified IEEE 10‐machine 39‐bus power system equipped with two FACTS devices and two WADCs. The feasibility and effectiveness of the proposed approach is verified by simulation studies.
Evaluation of data‐driven performance measures for comparing and ranking traffic bottlenecks
Authors: Hale David , Chrysikopoulos Georgios , Kondyli Alexandra , Ghiasi Amir 
Published: February 2021

AbstractTraffic analysis procedures are becoming more robust over time. However, there is still significant room for improvement both in practitioners’ adoption of robust methods and in robustness of the methods themselves. One example of oversimplified practice involves peak hour or 30th highest hour analysis, which fails to capture the impacts of varying demands and operating conditions. To address this limitation, detailed reliability modelling procedures were developed for the Highway Capacity Manual (HCM), but these procedures bring challenging input data and calibration requirements. A new generation of data‐driven tools is capable of real‐time congestion identification, but their performance measures are only beginning to improve and evolve. Finally, comparing and ranking congested locations (i.e. bottlenecks) on the basis of experience and judgment lacks credibility unless backed by quantitative results. This study discusses the development of new and innovative performance measures for congestion measurement. A case study of ranking eight real‐world bottlenecks based on the proposed measures and existing HCM measures produced new insights that could improve both approaches. Ideally, these new insights and methods would be accepted by agencies and/or commercial products for a new level of robustness in congestion measurement.
One‐step hydrothermal synthesis of double core‐shell oxygen‐incorporated molybdenum disulfide and its tribological properties
Authors: Chen Ying , Li Yuan , Liang Yuning , Chen Xuesong , Cui Jinjin 
Published: February 2021

AbstractUsing a simple one‐step hydrothermal method, benzyl triethylammonium chloride was used to assist the synthesis of double core‐shell oxygen‐incorporated molybdenum disulfide (DB‐O‐MoS2), and its friction and wear properties were measured on the MRS‐10A four‐ball testing machine. They were characterised by X‐ray diffraction, scanning electron microscope, transmission electron microscope, thermogravimetry, Brunner−Emmet−Teller and Fourier transform infrared spectroscope. Friction and wear properties of DB‐O‐MoS2 were measured at different concentrations. The results showed that the tribological properties of SN 5W‐40 base oil have been improved by adding the DB‐O‐MoS2 as lubricant additives. The possibility of DB‐O‐MoS2 mechanisms by which the nanolubricants improved the tribological properties were put forward. Therefore, research on DB‐O‐MoS2 is beneficial to the development of new engine lubricant additives.
Comment on ‘ElGamal cryptosystem‐based secure authentication system for cloud‐based IoT applications’
Authors: Irshad Azeem , Chaudhry Shehzad Ashraf 
Published: February 2021

AbstractThis comment is presented to identify the drawbacks in a recently demonstrated scheme by Maitra et al., SAS‐Cloud: doi:10.1049/iet-net.2019.0004, which adopted an ElGamal cryptosystem‐based technique for biometric authentication in cloud‐based IoT applications. In this protocol, the authors claim that their scheme provides mutual authentication. However, it is demonstrated in this article that the protocol merely supports unilateral authentication, which may result in clogging attack on the server's end. This is because the latter is unable to verify the authentication request in absolute terms, which might lead to resource clogging as well as denial of service attack affecting its Quality of Service (QoS).
The eddy current loss segmentation model of permanent magnet for temperature analysis in high‐speed permanent magnet motor
Authors: Zhang Meiwei , Luo Shifan , Liu Xiaoke , Li Weili 
Published: February 2021

AbstractThe rotor eddy current loss of high‐speed permanent magnet motor has an important influence on the temperature distribution of permanent magnet. In traditional method, the unbalanced distribution of eddy current in permanent magnet is ignored, and the eddy current loss is applied to the calculation of temperature field in the form of average heat density, which makes a certain error in the calculation of the temperature field in permanent magnet motors. This study proposes the 50 kW and 30,000 rpm high‐speed permanent magnet prototype and an eddy current loss segmentation model of permanent magnet. The unbalanced distribution of eddy current in permanent magnet is considered in this model, and the permanent magnet is divided into different regions. According to the eddy current loss segmentation model, the eddy current losses in different regions are obtained, then the heat density in different regions of permanent magnet is applied to the calculation of temperature field in the motor. The application of the proposed model is simple and convenient, and makes temperature simulation results closer to the actual situation. At the same time, in order to verify the accuracy of the model, the temperature calculation results using the proposed model are compared with the traditional method, and both the results are verified by relevant experiments.
Improved dynamic voltage restorer with reduced capacity of power inverter and energy storage for voltage sag mitigation
Authors: Guo Qi , Tu Chunming , Jiang Fei , Zhu Rongwu , Xiao Fan , Chen Cheng 
Published: February 2021

AbstractAs one of the most representative series active compensators, dynamic voltage restorer (DVR) can solve voltage‐related power quality uses effectively. The in‐phase voltage control and energy‐optimised control are the two typical control strategies of DVR. However, the in‐phase voltage control results in a large amount of active power exchange between the main grid and the dc link of DVR, and hence high capacity of storage system is needed in the dc link while the energy‐optimised strategy requires high injected voltage, resulting in oversizing of the DVR inverter. Thus, in order to avoid the aforementioned drawbacks, this study proposes a modified DVR, which connects an external capacitor in series with the LC filter (LCC) of DVR (LCC‐DVR). Based on the operational principles of the LCC‐DVR, an updated procedure of reference voltage is proposed to avoid overmodulation of DVR caused by load variations, ensuring the continuous operation capability of the LCC‐DVR. The overall control scheme of the LCC‐DVR and the comparative analysis among the proposed strategy and traditional strategies are also presented. The effectiveness of the proposed topology and method is clearly validated by the simulation and experimental results.
Seamless control for single‐phase high gain quasi‐switched impedance source multilevel inverter for distributed generation application
Authors: Thummalagunta Ajaykumar , Patne Nita R. , N Kodandaram 
Published: February 2021

AbstractThe single‐stage buck‐boost multilevel inverters are getting more attention even in low‐voltage and low power distributed generation applications due to high reliability with shoot‐through invulnerability. But the inherent boosting ability of most of the inventions is constrained by the device stresses and deprived performance at a low modulation index. In this study, a new hybrid quasi‐switched boost circuit is integrated with a reduced switch single‐phase multilevel inverter to accomplish a high gain single‐stage conversion at low device stress and high modulation index. It can be extended to a multi‐cell configuration for further enhancement of gain. Also, a control scheme is presented to achieve enhanced performance during standalone and grid‐connected modes. This scheme assists the need of providing reliable electrical supply to the critical local loads along with serving power to the main grid. It also provides islanding with a seamless transition for the period of grid failure. The proposed inverter's features, robustness, and flexibility of the control under both input voltage and output power disturbances make it more suitable for residential rooftop PV generation. A 500 W laboratory prototype is built for experimental verification. Both simulation and experimental studies validate the proposed theory.
Solar‐powered switched reluctance motor‐driven water pumping system with battery support
Authors: Mishra Anjanee Kumar , Singh Bhim 
Published: February 2021

AbstractThis work deals with the development of an efficient and reliable solar photovoltaic‐fed water pump with a battery energy storage (BES). This system ensures a continuous and rated supply of water in all working conditions. A new control logic for BES is developed, which significantly improves the overall response of the system. The support of the battery as a backup source is obtained through a bidirectional DC‐DC converter. Both the charging/discharging control and maximum power tracking of the solar panel are achieved through this bidirectional converter, whereas the voltage asymmetry compensation across split capacitors at DC link and motor drive controls are supervised by switched reluctance motor converter. The performance of the present scheme is examined through both simulated and experimental responses and is found adequate under all operational scenarios.
Optimal day‐ahead scheduling for active distribution network based on improved information gap decision theory
Authors: Ge Xiaolin , Zhu Xiaohe , Ju Xing , Fu Yang , Lo Kwok Lun , Mi Yang 
Published: February 2021

AbstractIn this study, information gap decision theory (IGDT) is reformed to formulate the uncertain parameters of wind power, photovoltaic and load. Traditional IGDT presumes that positive and negative deviations of uncertain parameters of the predicted value are equal, and it would result in imprecise assessment of fluctuated intervals. This study proposes an improved IGDT to overcome the inaccuracy of traditional IGDT by considering unsymmetrical fluctuation levels of uncertainties. For the operation and control of active distribution network, the non‐linear power flow constraints are included and linearised with a novel method based on circumscribed polyhedron approximation, which guarantees the accuracy of the solution results and takes less computing time. Additionally, from the mathematical point of view, the model established in this study is a multilevel optimisation problem, and linear Karush–Kuhn–Tucker conditions are formulated to transform the multilevel optimisation problem into a single‐level optimisation problem. Finally, the economic viability and model applicability are verified through the modified IEEE 33‐node distribution system.
Numerical investigation of inter‐blade cavitation vortex for a Francis turbine at part load conditions
Authors: Sun Longgang , Guo Pengcheng , Luo Xingqi 
Published: February 2021

AbstractInter‐blade cavitation vortex at part load has raised significant concerns about operation stability for Francis turbines due to tremendous development and integration of renewable energy resources into power grid. The principal objective of this study is to investigate the flow characteristics of inter‐blade cavitation vortex and its influence on pressure fluctuations for a low‐head Francis model turbine. Unsteady numerical simulations are carried out using shear stress transport turbulence model and Zwart cavitation model. Numerical results yield to a good validation with the experimental data. The findings show that inter‐blade cavitation vortices highlighted by cavitation structure and vortex structure are extremely different at the points adjacent to the incipient line of inter‐blade cavitation vortex. The location of inter‐blade cavitation vortex development in the runner is more sensitive to rotating speed than that to guide vane opening. The formation mechanism of inter‐blade cavitation vortex is attributed to flow separation in the vicinity of the runner hub. Pressure fluctuations induced by inter‐blade cavitation vortex are directly associated with the evolution of vapour volume in the runner and feature wide‐band and low‐frequency characteristic, and the fluctuations on the suction side of the runner blade are significantly magnified because of the presence of inter‐blade cavitation vortex.
An efficient and accurate Mixed‐integer linear programming model for long‐term operations of large‐scale hydropower systems
Authors: Zhao Zhipeng , Cheng ChunTian , Yan Lingzhi 
Published: February 2021

AbstractMixed‐integer linear programming is widely used in hydropower reservoirs operation optimisation because of its modelling flexibility, solution stability, and global search capability. A major obstacle to applying mixed‐integer linear programming to hydropower reservoirs operation optimisation, especially for long‐term operations of large‐scale hydropower systems, is the non‐linear phenomenon while converting water energy into electricity, which is normally expressed as a non‐linear bivariate function, that is, hydropower production function. To cross this technological barrier, a novel linearisation method for hydropower production function is proposed. The method uses rectangular meshing techniques to approximate hydropower production function. Then Special Ordered Sets of type 2 (SOS2)constraints are adopted for sub‐rectangle selection, which are formulated based on the binary branching schemes generated by binary reflected grey code. The proposed method can linearise the hydropower production function with only logarithmic‐sized binary variables of the traditional methods and maintain high accuracy. The method is then applied to optimising the operation of the Lancang River Basin hydropower system, which has 13 head‐dependent reservoirs with a deterministic model and a two‐stage stochastic model. The results show that the authors' method significantly outperforms conventional linearisation methods and can obtain accurate solutions within an acceptable time for deterministic and stochastic large‐scale hydropower reservoirs operation optimisation problems.
An enhanced MPPT algorithm based on adaptive extremum‐seeking control applied to photovoltaic systems operating under partial shading
Authors: Silveira Rafaela Dizaró , das Neves Gabriel Pereira , da Silva Sérgio Augusto Oliveira , Angélico Bruno Augusto 
Published: February 2021

AbstractThis study presents an improved extremum‐seeking control (ESC) method, intended to optimise the maximum power point tracking (MPPT) in a photovoltaic (PV) generation system. More specifically, to overcome the problem associated with partial shading in PV systems that leads to multiple operating points, an adaptive loop based on the measured PV array power is added to the conventional ESC. This procedure creates a variable amplitude of the perturbation signal and is able to accurately reach and track the global maximum power point (GMPP). The perturbation signal amplitude changes only when a predetermined power variation value is exceeded. As a result, this MPPT algorithm provides an efficient extraction of solar energy, avoids large oscillations in output response, and ensures the proper operation and performance of the system. The ESC theory is described in detail and the feasibility and effectiveness of the proposed approach are proved through simulation and experimental results. Furthermore, comparative tests show the proposed method's performance improvement, compared to the conventional ESC, evaluated in terms of convergence time, power oscillation in steady state, and accuracy to track the GMPP.
Logarithmic droop‐based decentralized control of parallel converters for accurate current sharing in islanded DC microgrid applications
Authors: P. Monica , M. Kowsalya , Guerrero Josep M. 
Published: February 2021

AbstractRemarkable progress in distributed power generation invigorated research into DC microgrids using a controllable DC–DC converter contingent to the functionalities therein. The study explores the circulating current issue in a parallel‐connected DC–DC converter and its associated current‐sharing capability. Despite, the conventional droop being a promising solution with less control complexity, the current sharing is achieved at an expense of voltage drop. The prime objective of this research work is to design a control strategy that guarantees a minimized circulating current with proper current sharing for a parallel‐operated DC–DC converter. This paper puts forth a dual reference‐based control to alleviate the droop and load effects of the system. The primary reference is generated by considering the effect of a marginal change in the input power of the converters. The virtual resistance‐based droop technique utilizes the prime reference for secondary droop reference generation. A current sharing algorithm is designed to assimilate adaptability to the scheme running under a variable line and load parameters. The comprehensive approach to the proposed control strategy has the advantages of improved current sharing and voltage regulation. A parallel DC–DC converter with the proposed control mechanism was investigated using MATLAB/Simulink and validated experimentally.
Preliminary analysis of long‐term storage requirement in enabling high renewable energy penetration: A case of East Asia
Authors: Du Ershun , Jiang Haiyang , Xiao Jinyu , Hou Jinming , Zhang Ning , Kang Chongqing 
Published: February 2021

AbstractIntegrating a high penetration of renewable energy for developing sustainable and low‐carbon electric energy system is becoming a common trend around the world. Many studies have evaluated the energy storage requirement for accommodating variable renewable energy (VRE). However, in the situation of high renewable penetration, there will be a huge potential requirement of long‐term energy storage for addressing the seasonal energy imbalance between VRE and load demand. Thus, a key element of evaluating the storage demand in enabling high VRE penetration is identifying the timescales of storage needed and the economic combination of long‐term and short‐term energy storages. This is neglected in existing researches. In this study, we quantitatively analyse the role of long‐term seasonal storage in enabling high VRE penetration. A generation expansion planning model is formulated to optimise the least‐cost generation portfolio with a renewable penetration target. Based on the proposed model, an empirical analysis for East Asia in 2050 is performed. The results indicate that (1) long‐term storage contributes to addressing the long‐term energy imbalance issue, (2) the optimal duration time of long‐term storage is around 720 h (a month), and (3) the long‐term storage becomes economical when the renewable penetration is above 70% (54.2% VRE penetration).
A new method for current–voltage curve prediction in photovoltaic modules
Authors: Peña Rafael , Diez‐Pascual Ana M. , Díaz Pilar García , Davoise Lara Velasco 
Published: February 2021

AbstractIn this work, a new method for obtaining the current–voltage curve for crystalline silicon and thin‐film flat panels is presented. It is based on the single‐diode model, with a variable shunt resistance and series resistance. New expressions for the shunt resistance and open circuit voltage as a function of the temperature and irradiance are deduced. Besides, a procedure to translate the series resistance to arbitrary conditions is proposed. The diode ideality factor and shunt resistance are obtained by optimization. The rest of the parameters that appear in the current–voltage curve are obtained from the module measurements by means of theoretical expressions. The procedure for obtaining the current–voltage curve under arbitrary operating conditions is also described. The results obtained with the developed model are compared with experimental measurements in cadmium telluride and amorphous silicon modules, and with results published in the literature for other technologies. The model faithfully reproduces the experimental values. For all the modules, the root mean square error for the maximum power is lower than 2% (below 1.5% in most cases). These errors are lower than those reported in the literature for other models. In particular, the results are significantly more exact in the case of thin‐film modules.
Control and optimisation of networked microgrids: A review
Authors: Islam Mojaharul , Yang Fuwen , Amin Mohammad 
Published: February 2021

AbstractMicrogrids (MGs) have become an integral part of smart grid initiatives for future power system networks. Networked microgrids consist of several neighbouring microgrids connected in a low/medium distribution network. The primary objective of a network is to share surplus/shortage power with neighbouring microgrids to achieve mutual cost‐effective operation, utilising green energy from renewable energy resources in the network and increasing the reliability of customer service. This article classifies networked microgrids on the basis of network formation and provides an overview of recent research on control of networked microgrids. In addition, a state‐of‐the‐art review of optimisation methods is provided to solve the energy optimisation problem in networked microgrids. Furthermore, the advantages and challenges of the networked operation of microgrids are presented as for possible research directions in the future.