bluuebunny/crossref_metadata_2025 huggingface dataset:
N-terminal-mediated oligomerization of DnaA drives the occupancy-dependent rejuvenation of the protein on the membrane
Authors: Aranovich Alexander , Braier-Marcovitz Shani , Ansbacher Esti , Granek Rony , Parola Abraham H. , Fishov Itzhak
Published: August 2015

DnaA, the initiator of chromosome replication in most known eubacteria species, is activated once per cell division cycle. Its overall activity cycle is driven by ATP hydrolysis and ADP–ATP exchange. The latter can be promoted by binding to specific sequences on the chromosome and/or to acidic phospholipids in the membrane. We have previously shown that the transition into an active form (rejuvenation) is strongly co-operative with respect to DnaA membrane occupancy. Only at low membrane occupancy is DnaA reactivation efficiently catalysed by the acidic phospholipids. The present study was aimed at unravelling the molecular mechanism underlying the occupancy-dependent DnaA rejuvenation. We found that truncation of the DnaA N-terminal completely abolishes the co-operative transformation between the high and low occupancy states (I and II respectively) without affecting the membrane binding. The environmentally sensitive fluorophore specifically attached to the N-terminal cysteines of DnaA reported on occupancy-correlated changes in its vicinity. Cross-linking of DnaA with a short homobifunctional reagent revealed that state II of the protein on the membrane corresponds to a distinct oligomeric form of DnaA. The kinetic transition of DnaA on the membrane surface is described in the present study by a generalized 2D condensation phase transition model, confirming the existence of two states of DnaA on the membrane and pointing to the possibility that membrane protein density serves as an on-off switch in vivo. We conclude that the DnaA conformation attained at low surface density drives its N-terminal-mediated oligomerization, which is presumably a pre-requisite for facilitated nt exchange.
Editor's Perspective: Research Article Versus Research Note
Authors: Wilkinson Krista
Published: August 2015

Purpose

In this article, the Editor of the
American Journal of Speech-Language Pathology
reflects on the distinction between two article types—the Research Article and the Research Note—and the important contributions that each article type makes.
Analysis of maximum traffic intensity under pre‐set quality of service requirements in low earth orbit mobile satellite system for fix channel reservation with queueing handover scheme
Authors: Liao Mingxia , Liu Yuan'an , Hu Hefei , Yuan Dongming
Published: August 2015

Maximum traffic intensity supported by a low earth orbit mobile satellite system (LEO‐MSS) is important in practical application for providing satisfactory service. Applying fix channel reservation with first in first out queueing handover scheme into LEO‐MSS, a novel analytical approach is proposed for determining the maximum traffic intensity under pre‐set quality of service (QoS) constraints on new call blocking probability and handover failure probability. The relationship between QoS constraints and maximum traffic intensity is established. The expression of maximum traffic intensity is then deduced. The optimal number of reserved channels is obtained. By comparing the results between the proposed approach and existing method, the correctness of the proposed approach is verified. The proposed approach greatly reduces the calculation complexity. Lastly, the accuracy of the analysis has been verified by computer simulations.
Heterogeneous state estimation in dynamic networked systems
Authors: Sijs Joris , van den Bosch Paul
Published: August 2015

Distributed state estimation refers to a method for computing a local estimate of the global state in each node of a networked systems. Typically, current methods take a homogenous approach, where the same estimator is performed in each node for approximating a centralised estimation result. Yet, many practical examples indicate that the capabilities of a networked systems rise when its nodes do not only have similarities, but, to some extent, differ from each other. Inspired by this idea, this study extends current studies on homogeneous estimation and turns it into a heterogeneous solution for distributed state estimation focusing on three contributions. Firstly, the estimation problem in networked systems is reformulated so that a particular interdependency of the estimation results between any two nodes is pursued rather than aiming for similar estimation results across all nodes. Secondly, a node setup is adopted suiting heterogeneous estimation on system level, yet, still allows for nodes to employ solutions based on existing (homogenous) distributed estimators. Thirdly, the pursued interdependency of local estimation results is proven for the adopted setup, along with practical conditions that will guarantee stable estimation results in each node locally. Extended designs of this heterogeneous estimator are studied for observing the spread of a chemical compound (linear) and for detecting shockwaves on a highway (non‐linear).
Refined Jensen‐based inequality approach to stability analysis of time‐delay systems
Authors: Van Hien Le , Trinh Hieu
Published: August 2015

In this study, the authors derive some new refined Jensen‐based inequalities, which encompass both the Jensen inequality and its most recent improvement based on the Wirtinger integral inequality. The potential capability of this approach is demonstrated through applications to stability analysis of time‐delay systems. More precisely, by using the newly derived inequalities, they establish new stability criteria for two classes of time‐delay systems, namely discrete and distributed constant delays systems and interval time‐varying delay systems. The resulting stability conditions are derived in terms of linear matrix inequalities, which can be efficiently solved by various convex optimisation algorithms. Numerical examples are given to show the effectiveness and least conservativeness of the results obtained in this study.
Functional observer for switched discrete‐time singular systems with time delays and unknown inputs
Authors: Lin Jinxing , Shi Yang , Gao Zhifeng , Ding Jie
Published: August 2015

This study considers the functional observers design for a class of discrete‐time switched singular systems simultaneously subject to state delays, unknown inputs (UIs) and arbitrary switching sequences. The singular matrix E is assumed to be switching‐mode‐dependent, and the UIs are present in both the state and the measurement channels. A mode‐dependent, delay‐type observer is first constructed, then, based on the unknown input decoupling and the switched Lyapunov theory, a method is proposed to design such observer which ensures both: the total elimination of the UIs and exponential estimate of the given function of the state vector. The conditions for the existence of the proposed observer are given through algebraic matrix inequalities, and exponential stability of the observation error dynamics is derived by using a properly constructed decay‐rate‐dependent switched Lyapunov function and the linear matrix inequality technique. Finally, an illustrative example is given to show the effectiveness of the obtained results.
Cooperative output regulation for a class of non‐linear multi‐agent systems
Authors: Zhenxing Li , Haibo Ji , Jie Sheng
Published: August 2015

In this study, the authors consider the consensus output regulation problem for a class of non‐linear multi‐agent systems with subsystems have the same relative degree. The multi‐agent system is heterogeneous that means subsystems may have different dynamics. The author's goal is to design a dynamic controller such that the outputs of subsystems follow a desired trajectory which is the output of exosystem. A recursive procedure and internal model are employed to achieve this goal.
Adaptive position feedback consensus of networked robotic manipulators with uncertain parameters and communication delays
Authors: Wang Lijiao , Meng Bin
Published: August 2015

In this study, the authors address the leaderless consensus problem of multiple robotic manipulators with communication delays. Taking dynamic uncertainties of the robotic agents into consideration, they perform the distributed adaptive position feedback control scheme design for strongly connected information topology, where the communication is subject to constant and bounded time delays. The novel distributed sliding observer is first proposed such that the joint velocities can be estimated online. Then, the distributed adaptive controller with dynamic parameter updating is constructed based on the observed information. The convergence of consensus errors is proved with Lyapunov stability analysis tool. Finally, simulations are performed on networked robotic manipulators to validate the effectiveness of the theoretical approach.
Event‐triggered consensus of Markovian jumping multi‐agent systems via stochastic sampling
Authors: Hu Aihua , Cao Jinde , Hu Manfeng , Guo Liuxiao
Published: August 2015

This study investigates the issue of mean square consensus for multiple agents connected by a directed network. The graph of the network is supposed to have a spanning tree and each agent is taken as a Markovian jumping system. By utilising the event‐triggered strategy, some sufficient conditions for consensus are presented whether the transition rates for the Markov chain being completely known or not. Furthermore, the event‐triggered function designed in this study is dependent on the stochastic sampled‐data from neighbouring agents. Theoretical results are provided according to the graph theory, Lyapunov functional and linear matrix inequality approach. Finally, a numerical example is given to demonstrate the effectiveness of the theoretical analysis.
Adaptive neuro‐fuzzy sliding mode control guidance law with impact angle constraint
Authors: Li Qingchun , Zhang Wensheng , Han Gang , Yang Yehui
Published: August 2015

This study presents a guidance law to intercept non‐manoeuvring targets at a desired impact angle. The desired impact angle, defined in terms of a desired line‐of‐sight angle, is achieved by selecting the missile's lateral acceleration to enforce the sliding mode on a sliding surface. Then, the authors use the Lyapunov stability theory to prove the stability of the proposed non‐linear sliding surface. Furthermore, they introduce the adaptive neuro‐fuzzy inference system (ANFIS) to adaptively update the additional control command and reduce the high‐frequency chattering of sliding mode control (SMC). The proposed guidance law, denoted ANFSMC guidance law with impact angle constraint, combines the SMC methodology with ANFIS to enhance the robustness and reduce the chattering of the system. The effectiveness of the ANFSMC guidance law is also verified by the numerical simulations.
Optimal control for rail vehicle pantograph systems with actuator delays
Authors: Lin Yu‐Chen , Shieh Niahn‐Chung , Liu Van‐Tsai
Published: August 2015

This study exploits an optimal control approach for solving the general robust control problem of active pantograph suspension systems with actuator delays and time‐varying contact force such that both the stabilisation and optimal performance are achieved. On the basis of Bellman's optimality principle and Razumikhin theorem, the general robust control design problem can be equivalently transformed into an optimal control problem with the amount of matched uncertainties involved in the performance index. A stability criterion has been developed under which the time varying stiffness of contact force and time‐delayed actuation force can not only achieve stability, but also acquire the guaranteed level of performance for regulation. A suitable linear state feedback control law is characterised via Lyapunov stability theory to ensure quadratic stability and performance robustness of the closed‐loop systems. The effectiveness of the proposed design is demonstrated through simulation studies.
Stochastic finite‐time consensualisation for Markov jump networks with disturbance
Authors: Luan Xiaoli , Min Yang , Ding Zhengtao , Liu Fei
Published: August 2015

This study is devoted to the finite‐time consensus control for directed networks with stochastic Markov jump topologies and external disturbances. The purpose of the study is to design a control protocol to ensure that the disagreement dynamics of interconnected networks stay in a given bound over a finite‐time interval rather than asymptotically converge to zero in infinite settling time. Through utilisation of certain features of Laplacian matrix in real Jordan form, sufficient conditions for the existence of finite‐time consensus protocol is derived by allowing Lyapunov function to increase in a fixed‐time interval. Finite‐time convergence result for stochastic consensus problem is validated via a simulation study.
Event‐triggered feedback for power allocation in wireless networks
Authors: Campos‐Delgado Daniel Ulises , Rojas Alejandro J. , Luna‐Rivera Jose Martin , Gutiérrez Carlos A.
Published: August 2015

Transmission power control constitutes a core feature required to achieve a desired quality of service in wireless networks. A practical implementation calls on the intuition of using limited resources, only when are strictly required. Thus, the appeal of an event‐triggered scheme arises naturally over more traditional, but less efficient, periodic time‐triggered control solutions. Motivated by these ideas, the authors present here a power allocation strategy based on an event‐triggered transmission (ETT) to reduce the feedback signalling in the network. The power allocation under ETT is based on a nominal control that guarantees internal stability and performance. Hence, if the feedback signalling does not change significantly from the previous sample, no feedback transmission is assigned to reduce bandwidth usage. Two schemes are employed to define the ETT while preserving closed‐loop stability: a piecewise quadratic Lyapunov argument and a perturbed linear system approach. These two approaches establish a trade‐off between complexity and conservativeness. The power allocation under ETT was thoroughly evaluated under two nominal control schemes to establish a relation between performance and feedback reduction.
Observer‐based adaptive consensus tracking for linear multi‐agent systems with input saturation
Authors: Chu Hongjun , Yuan Jingqi , Zhang Weidong
Published: August 2015

This study considers the observer‐based consensus tracking problem of linear multi‐agent systems with input saturation. Existing observer‐based consensus protocols are designed based on an undirected graph, and need global information, such as the network size or eigenvalue information of the Laplacian matrix. In this study, based on only the agent dynamics and the relative outputs of neighbouring agents, an adaptive consensus protocol is proposed by assigning a time‐varying coupling weight to each node, and this protocol is independent of any global information and hence is fully distributed. Under the assumptions that each agent is asymptotically null controllable with bounded controls and detectable, and the topological graph has a directed spanning tree with the leader as the root node, semi‐global observer‐based consensus tracking of multi‐agent systems can be reached despite actuator saturation occurring. The results are applied to consensus tracking control of two‐mass‐spring systems, which are well‐known models for vibration in many mechanical systems.
Frequency selective learning model reference adaptive control
Authors: Höcht Leonhard , Maity Arnab , Holzapfel Florian
Published: August 2015

This study proposes a new frequency selective learning adaptive control approach for model reference adaptive control systems to improve their adaptation performance without depending on high learning rates. It is developed by inspiration from the philosophies of the Q ‐modification and concurrent learning approaches and retains the key advantages of both. The philosophy of this proposed approach is that the known part of the plant dynamics passes through multiple filters. By constraint of the governing dynamic equations, this result equals an expression containing the unknown parameters in a filtered version, which is used for augmentation of the update law. The use of multiple filters aims at increasing the rank of the update law based on online instantaneous information and for a sufficient number of filters at different bandwidths, exponential stability can be achieved in the presence of the structured matched uncertainty. Moreover, it can cope with a sudden change of the system configuration. As a result, it leads to an efficient adaptive control approach. Furthermore, a challenging roll control problem of an aircraft demonstrates the usefulness of this proposed approach.
Wide‐area power system stabiliser based on model‐free adaptive control
Authors: Lu Chao , Zhao Yi , Men Kun , Tu Liang , Han Yingduo
Published: August 2015

The interconnection of regional power grids has resulted in inter‐area low‐frequency oscillation, which has become a serious problem that threatens the security of power systems. Wide‐area power system stabiliser (WAPSS) is an effective device to damp this oscillation. Given that the interconnected multi‐machine power system is a strongly non‐linear and complex system with time‐varying structure and operating conditions, satisfactory control performance of WAPSS is difficult to obtain by using conventional model‐based control methods. In this study, a data‐driven control method called model‐free adaptive control (MFAC) is introduced to WAPSS design. The MFAC algorithm is improved to meet the wide‐area damping control requirements in consideration of system disturbances. The stability of the closed‐loop system with the improved MFAC‐WAPSS is also analysed, and the parameter settings of the improved MFAC algorithm are provided in detail. The improved MFAC‐WAPSS can adjust its parameters adaptively only based on the input and output data and avoid the complex system modelling process. The proposed adaptive WAPSS is evaluated on a simplified New England power system. Simulation results show the effectiveness of this new technique.
Neural‐network‐based adaptive leader‐following consensus control for second‐order non‐linear multi‐agent systems
Authors: Wen Guo‐Xing , Chen C.L. Philip , Liu Yan‐Jun , Liu Zhi
Published: August 2015

In this study, a novel adaptive neural network (NN)‐based leader‐following consensus approach is proposed for a class of non‐linear second‐order multi‐agent systems. For the existing NN consensus approaches, to obtain the desired approximation accuracy, the NN‐based adaptive consensus algorithms require the number of NN nodes to must be large enough, and thus the online computation burden often are very heavy. However, the proposed adaptive consensus scheme can greatly reduce the online computation burden, because the adaptive adjusting parameters are designed in scalar form, which is the norm of the estimation of the optimal NN weight matrix. According to Lyapunov stability theory, the proposed approach can guarantee the leader‐following consensus behaviour of non‐linear second‐order multi‐agent systems to be obtained. Finally, a numerical simulation and a multi‐manipulator simulation are carried out to further demonstrate the effectiveness of the proposed consensus approach.
Further results on stability and stabilisation of switched positive systems
Authors: Zhang Junfeng , Huang Jun , Zhao Xudong
Published: August 2015

This study is concerned with stability and stabilisation of switched positive systems in both continuous‐ and discrete‐time contexts. Several criteria of Metzler/Hurwitz and non‐negative/Schur matrices are presented. By using these criteria and dual system theory, a sufficient condition for stability of switched positive systems is established. On the basis of the sufficient condition, a new controller design is proposed for switched positive systems. It is shown that the proposed design reduces the conservatism of the existing approaches in the literature where the controller gain matrices always have the property of being rank one. The results are also extended to discrete‐time systems. Finally, two illustrative examples verify the validity of the theoretical findings.
Stability analysis for neutral stochastic linear system
Authors: Li Boren , Liu Xueliang
Published: August 2015

This study is a further note on stability analysis for uncertain linear neutral stochastic system. Firstly, the stability of linear neutral stochastic system with mix delays is studied. By employing a new Lyapunov–Krasovskii functional and novel method to estimate the integral terms, the less conservative stability criteria are obtained. Compared with previous results, the novel method can sufficiently utilise more negative items information. Then, in virtue of the Schur complement and linear matrix inequality technique, the robust stability of the uncertain neutral stochastic system is derived, which have less conservatism. Finally, two numerical examples show that the authors’ results are effective and less conservative than other reports in the previous literature.
Multi‐input and multi‐output proportional‐integral‐derivative controller design via linear quadratic regulator‐linear matrix inequality approach
Authors: Pradhan Jatin K. , Ghosh Arun
Published: August 2015

This study considers the problem of designing a multi‐input and multi‐output (MIMO) proportional‐integral‐derivative (PID) controller via direct optimal or suboptimal linear quadratic regulator (LQR) approach. To design the controller, first the MIMO PID design problem is transformed into a state feedback control and then the gains of the state feedback controller are chosen through an optimal or suboptimal LQR design. Given a minimal state space representation (A, B, C) of the plant, a necessary and sufficient condition (based on matrices A, C) for which the optimal problem (i.e. PID design via optimal LQR) is solvable is obtained. When this optimal problem is not solvable, a suboptimal solution (i.e. PID design via suboptimal LQR), if exists, is obtained by converting the problem into trace minimisation one, which is solved using linear matrix inequality‐based method. Suitable examples are considered to illustrate the approaches.
Backstepping dynamic surface control for a class of non‐linear systems with time‐varying output constraints
Authors: Qiu Yanan , Liang Xiaogeng , Dai Zhiyong , Cao Jianxiong , Chen YangQuan
Published: August 2015

The barrier Lyapunov function (BLF) and its variants such as the asymmetric barrier Lyapunov function (ABLF) combined with backstepping technique have recently been employed to handle constraints for a class of non‐linear systems. However, the repeated differentiation in backstepping will result in the requirement of high‐order differentiability and the complexity of controllers in the multiple‐state high‐order systems. This study introduces dynamic surface control (DSC) to deal with these problems. The authors propose a backstepping DSC scheme based on the ABLF to address time‐varying output constraints for a class of non‐linear systems. The proposed control scheme can avoid the proliferation and singularity of repeated differentiation. As a consequence, it can relax the requirements of high‐order differentiability for stabilising functions and high power of output tracking error transformation involved in ABLF synthesis. The new controller can be proved to guarantee that all the closed‐loop signals remain bounded, and to ensure output constraints never violated. Comparison studies with previous work validate that DSC incorporated with ABLF can achieve favourable performance bounded within constraints, and it can also ensure fast and stable tracking convergence in the presence of disturbance. Experimental results illustrate the effectiveness of the presented method.
Identification and control for Hammerstein systems with hysteresis non‐linearity
Authors: Gao Xuehui , Ren Xuemei , Zhu Changsheng , Zhang Chengyuan
Published: August 2015

Identification and composite control of Hammerstein system with unknown order linear dynamics and a static hysteresis non‐linearity modelled by Preisach operator is investigated. The order of linear dynamics is firstly determined by Hankel matrix approach and then a blind identification is implemented to identify the linear dynamics based on the over‐sampling output measurements only. Then a novel deterministic approach is proposed to identify the Preisach model for hysteresis non‐linearity, which is devoted to identify a triangle matrix. This novel approach needs less dimensions to obtain Preisach density function than other existing methods. Finally, a composite control consisting of discrete inverse model‐based controller (DIMBC) and discrete adaptive sliding mode controller (DASMC) is developed to achieve tracking control. The composite control can reduce the reaching time of DASMC and improve the robustness of DIMBC. Experiments based on a turntable servo system demonstrate the effectiveness of the proposed identification and control methods.
Optimal quantisation for random parameter estimation
Authors: Wu Hao
Published: August 2015

In this study, the optimal quantiser design for random parameter estimation is investigated. The objective is to find a quantiser to minimise the variance of the estimation error by the minimum mean‐square estimation. The main results are presented for the cases of high and low resolutions, respectively. For high resolution, multi‐dimensional quantisation is considered and a quantitative relationship between the quantisation density and the probability density function is presented. For low‐resolution case, an indirect method is developed for one‐dimensional optimal quantisation by exploiting the results of high resolution case. The measurement space is first evenly divided into a number of small intervals, then the quantisation is approximately represented by the grouping of the small intervals. At last, a dynamic programming‐based method is presented for the optimal grouping.
Absolute stability analysis of non‐linear active disturbance rejection control for single‐input–single‐output systems via the circle criterion method
Authors: Li Jie , Xia Yuanqing , Qi Xiaohui , Gao Zhiqiang , Chang Kai , Pu Fan
Published: August 2015

This study focuses on the stability analysis of non‐linear active disturbance rejection control (ADRC) for single‐input–single‐output systems. Firstly, a non‐linear ADRC system for a linear plant is transformed into a Lurie system. Secondly, two extended circle criteria are obtained, and two numerical examples are presented to illustrate the absolute stability analysis, including both stable and unstable linear plants. Thirdly, local asymptotic stability of a non‐linear ADRC system for a non‐linear plant is also performed through linearisation by Taylor expansion. Finally, a comparison with the existed processing methods is further made, including the describing function method and time domain stability analysis method. It can be concluded that the circle criterion method is more convenient and practical for its frequency domain and graphical interpretation. The circle criterion method can also be extended to the stability analysis of a control system which applies linear ADRC to a plant with one non‐linear term.
Earth fault location based on evaluation of voltage sag at secondary side of medium voltage/low voltage transformers
Authors: Topolanek David , Lehtonen Matti , Adzman Mohd Rafi , Toman Petr
Published: August 2015

The main reasons for installation of power quality meters in distribution transformer substations are power quality monitoring and global evolution of electrical network towards the ‘smart grid’. In case that all measurements from the meters are properly synchronised and centralised, new possibilities of control or evaluation of the network are enabled. This contribution proposes the possibility for an earth fault localisation with the aid of synchronised data recorded on the low‐voltage side of the medium voltage/low voltage transformers in compensated neutral distribution networks which are equipped with auxiliary resistor for short‐time increasing of the active part of the fault current. The described method uses voltage sags evoked by connecting of the auxiliary resistor for locating the faulty section. The proposed method is tested with the help of numerical model which presents a part of the distribution network.
Application of Bayesian networks in composite power system reliability assessment and reliability‐based analysis
Authors: Eliassi Mojtaba , Khoshkholgh Dashtaki Ali , Seifi Hossein , Haghifam Mahmoud‐Reza , Singh Chanan
Published: August 2015

Bayesian network (BN) is a strong framework for handling probabilistic events which have received limited attention in power system reliability assessment. By applying BN for bulk power system reliability assessment, additional capabilities are provided at modelling and analysis levels in comparison with conventional methods. This study proposes a methodology to apply BNs to composite power system (CPS) reliability modelling, reliability assessment and reliability‐based analyses. A minimal cutset (MC)‐based method is proposed to extract the BN structure. Moreover, BN parameters are defined based on logical relationships between components, MCs and system failure. In addition, some issues of BN application to large systems are investigated. A variety of reliability‐based analyses, useful in different power system studies are introduced and discussed in details which are provided by applying BNs to CPS reliability. The computational efficiency of the presented method is demonstrated by comparing it with state enumeration and Monte Carlo simulation methods. The proposed methodology is implemented on Roy Billinton Test System to extract its BN model based on which analysis issues are considered. Finally, the proposed methodology is applied to the simple, but representative, system the IEEE‐reliability test system to show its feasibility in larger systems.
Transition from alternating current to direct current low voltage distribution networks
Authors: Antoniou Dimitris , Tzimas Antonios , Rowland Simon M.
Published: August 2015

Maximising the capacity of the existing alternating current (AC) distribution network infrastructure by conversion to direct current (DC) may hold significant advantages. In particular it may provide a greater flow of electrical energy within urban areas, allowing a lower investment cost for adoption of electrical vehicles and domestic heating. Integration with Smart Grid applications will require maintained levels of reliability, and improved efficiency and flexibility. The transition of the cable infrastructure from the legacy low voltage AC system to low voltage DC is considered in this study. In particular this study investigates the limitations of DC supplied through the existing distribution network without major re‐construction, and proposes optimal configurations that could be adopted in a smart‐DC distribution network. The implications for power flow in the network are considered with regards to existing cable limitations. It is concluded that a better understanding of cable and joint reliability is required before such changes are made to existing LV networks.
Computation of transient voltage and current profiles along illuminated multiconductor lines by means of the numerical Laplace transform
Authors: Nuricumbo‐Guillén Rodrigo , Gómez Pablo , Espino‐Cortés Fermín Pascual
Published: August 2015

In this study, a transmission line model described in the q–s domain (spatial frequency–temporal frequency) is applied to obtain transient voltage and current profiles along field‐excited multiconductor lines (also known as illuminated lines). The incident field excitation is incorporated into the model by means of Taylor's formulation, in which such field is included by means of series voltage and shunt current sources distributed along the line. For the case of lines excited by an indirect lightning stroke, the corresponding field is computed according to the formulae proposed by Master and Uman. The inverse numerical Laplace transform is applied successively (twice) to obtain the results in the z–t domain, corresponding to the voltage and current profiles along the illuminated line. An initial validation of the model consists of two examples, in which simple analytical expressions are introduced for the voltage and current sources (separately) along the line in order to provide comparisons with alternative transients programme/electromagnetic transients programme. Then, three test cases corresponding to lightning strokes at different locations near the line are considered. Power system computer‐aided design/electromagnetic transient design and control is used in this section for validation purposes.
Improved fault location algorithm for multi‐location faults, transforming faults and shunt faults in thyristor controlled series capacitor compensated transmission line
Authors: Swetapadma Aleena , Yadav Anamika
Published: August 2015

Fault location estimation in series compensated transmission lines is quite difficult because a non‐linear current dependent circuit appears between the substation and fault point. In particular, the faults which occur at different locations at the same time in different phases known as multi‐location faults has not been addressed by researchers. Other types of fault that may occur in transmission lines are transforming faults where one type of fault transforms to another type fault after some time. In this study, a fault location estimation scheme using artificial neural network (ANN) is presented for multi‐location faults, transforming faults as well as for commonly occurring shunt faults in thyristor controlled series capacitor (TCSC) compensated transmission line. DB‐4 wavelet is used for pre‐processing of the three‐phase current and voltage signals. The shunt capacitance of the line is considered based on distributed parameter line model. Feasibility of the ANN‐based fault location algorithm is tested under a wide variation of parameters, such as fault type, location, fault resistance and fault inception angle. Fault location errors are within 0.001–1% range.
Simple method of fast discharge of capacitor banks using delta connected transformers: modelling and experimental testing
Authors: Fracalossi Daniel Anthony , Haque Md Enamul , Davies Mark
Published: August 2015

The discharge of capacitor banks at substations is necessary before their connection to the grid can occur. This study investigates the use of delta‐connected transformers for capacitor discharge. The energy from the capacitor banks is discharged by driving the transformers into saturation after disconnection from the grid. To investigate this, simulations were conducted in PSCAD to identify the relationship between the size of the transformer, the size of discharge resistor and the time taken for the capacitor bank to discharge. To confirm the accuracy of the PSCAD simulations, a scaled physical model was constructed in the laboratory and discharge results were recorded. A PSCAD simulation of the scaled model was also created to directly compare the accuracy of PSCAD. It was found that PSCAD produced accurate representations of the laboratory model, resulting in a greater confidence in the full‐scale results.
Multi‐objective planning tool for the installation of renewable energy resources
Authors: Bouhouras Aggelos S. , Sgouras Kallisthenis I. , Labridis Dimitris P.
Published: August 2015

This study examines how environmental and socioeconomic criteria affect renewable energy resources (RES) distribution strategic plans regarding national energy policies. Four criteria are introduced with respective coefficients properly formulated to quantify their capacity. Moreover, these coefficients are properly normalised to combine the effect of each criterion under a uniform formulation. The base case scenario in this work considers an initially available capacity of RESs to be equally distributed among the candidate regions. Six scenarios about different prioritisation are examined. The results prove that different prioritisation criteria yield significant variations regarding the assigned regional RES capacity. The proposed algorithm defines optimisation only by terms of predefined prioritisation criteria; each solution could be considered optimal given that the respective installation strategic plan is subject to specific weighted criteria. The advantages of the proposed algorithm rely on its simplicity and expandability, since both coefficients formulation and resizing procedure are easily performed, as well as additional criteria could be easily incorporated in the resizing procedure. Thus, this algorithm could be considered as a multi‐objective planning tool regarding long‐term strategic plans for nationwide RES distribution.
Robust stabilisation of power systems with random abrupt changes
Authors: Soliman Hisham , Shafiq Muhammad
Published: August 2015

This study considers the stabilisation of power systems subject to random jumps. Transient, permanent faults of power lines, and the consequent switching of the associated circuit breakers are represented as a discrete‐time Markov chain. The controller is designed for Markov jump linear systems based on transition probabilities obtained from statistical data of the faults. The linear matrix inequalities framework is used as a tool for designing the proposed controller. The controller provides desired performance swiftness via regional pole placement with the constraint of system load variations and random variations in the topology. The effectiveness of the power system stabiliser is studied on a single‐machine infinite‐bus and multi‐machine systems.
Analysis of power transfer limit considering thermal balance of overhead conductor
Authors: Dong Xiaoming , Kang Chongqing , Sun Hua , Zhang Ning
Published: August 2015

Series resistances of overhead transmission lines (OTLs) are largely dependent on the corresponding conductor temperature. The electric current heats the conductor, and the environmental conditions affect the thermal exchange. Therefore, multiple factors related to the thermal balance codetermine the conductor temperature and resistance. However, the traditional power flow analysis neglects the thermal balance effects by treating those related factors as invariables, which may introduce some errors because of the change of the factors. Therefore, in this study, new power flow formulations, which allow for the relationship between the transmission power flow and the thermal balance, are derived. This study demonstrates the errors by applying the new formulations to calculate the power transfer limit (PTL). Moreover, the PTL of the OTL is defined either by encountering the thermal rating (TR) or the steady‐state stability limit. A case study based on an equivalent 2‐bus test system was used to illustrate the efficacy of the thermal balance that affects the PTLs of both types. In this analysis, this study also reveals the relationship between the TR and steady‐state stability limit with various physical and environmental conditions.
Reactive power planning under high penetration of wind energy using Benders decomposition
Authors: Fang Xin , Li Fangxing , Wei Yanli , Azim Riyasat , Xu Yan
Published: August 2015

This study addresses the optimal allocation of reactive power volt‐ampere reactive (VAR) sources under the paradigm of high penetration of wind energy. Reactive power planning (RPP) in this particular condition involves a high level of uncertainty because of wind power characteristic. To properly model wind generation uncertainty, a multi‐scenario framework optimal power flow that considers the voltage stability constraint under the worst wind scenario and transmission N − 1 contingency is developed. The objective of RPP in this study is to minimise the total cost including the VAR investment cost and the expected generation cost. Therefore RPP under this condition is modelled as a two‐stage stochastic programming problem to optimise the VAR location and size in one stage, then to minimise the fuel cost in the other stage, and eventually, to find the global optimal RPP results iteratively. Benders decomposition is used to solve this model with an upper level problem (master problem) for VAR allocation optimisation and a lower problem (sub‐problem) for generation cost minimisation. Impact of the potential reactive power support from doubly‐fed induction generator (DFIG) is also analysed. Case studies on the IEEE 14‐bus and 118‐bus systems are provided to verify the proposed method.
Sparse S‐transform for location of faults on transmission lines operating with unified power flow controller
Authors: Tripathy Loknath , Samantaray Subhransu Ranjan , Dash Pradipta Kishore
Published: August 2015

This study presents a new fault location algorithm for a transmission line operating with a unified power flow controller (UPFC). The proposed algorithm is based on a new matrix version of the conventional S‐transform called sparse S‐transform (SST), using selected frequency components to increase the speed of the computation significantly. A variety of faults are initiated before and after the location of UPFC on the transmission line using MATLAB/SIMULINK platform. Further, the impedance trajectories and fault location are estimated using SST with significant accuracies. The computational speed of the SST is almost 30 times faster than the conventional discrete S‐transform which makes it a suitable candidate for real‐time application in digital relaying.
Induced voltages on overhead transmission lines because of nearby included lightning channel
Authors: Abouzeid Said I. , Shabib Gaber , Mohamed Adel Zein El Dein
Published: August 2015

The power system networks can be adversely affected by indirect coupling with the cloud‐to‐ground lightning return stroke. In most computations of lightning‐induced voltages on overhead transmission lines, the overhead transmission lines are considered as straight lines and the return stroke channel is assumed to be a straight and a vertical channel. However, in reality, the line is not straight and is not parallel to the ground level because of the sag produced by its weight. In addition, the lightning channel is most often inclined. This study studies the effect of conductors’ sag as well as the inclination angle of the lightning channel on the lightning‐induced voltage on the three‐phase power lines because of inclined lightning channel. This study has been evolved, formulated and applied on Egyptian 500 kV three‐phase transmission line. Moreover, the effect of the ground conductivity on induced overvoltages in case of sagged transmission lines is considered. It can be observed that, taking into account the effects of the ground conductivity, the presence of the ground wire and the sag of the transmission lines reduce the values of the calculated induced voltages.
Probabilistic evaluation for static voltage stability for unbalanced three‐phase distribution system
Authors: Ran Xiaohong , Miao Shihong
Published: August 2015

To investigate the impact of the randomness of renewable energy generation on distributed network, the authors propose a non‐linear three‐phase maximum loadability model. Considering uncertainty such as wind power generation and load forecasting deviation, a probabilistic evaluation of static voltage stability for distributed network is presented based on cumulants method. Correlations between adjacent wind farms are also considered. Maximal load increment models of three‐phase balanced/unbalanced power system are solved by improved self‐adaptive particle swarm optimisation algorithm. Two approximation expansions named Cornish–Fisher expansion and Gram–Charlier expansion are employed to obtain probability distribution of random variables. Relation of probabilistic performances including means and variances between balanced system and unbalanced system could be obtained. 25‐bus/33‐bus unbalanced system and 33‐bus balanced system are studied as examples to validate effectiveness of their proposed method, and results based on cumulants method are compared with Monte Carlo simulations.
Market‐based mechanism for multi‐area power exchange management in a multiple electricity market
Authors: Karimi Ali , Seifi Hossein , Sheikh‐El‐Eslami Mohammad Kazem
Published: August 2015

The cross‐border trading in an interconnected multi‐area power system (MAPS) has significantly increased in recent years. In this situation, the coordination of electricity markets in MAPS is very imperative. In this study, in the presence of multiple markets in an MAPS structure, it is assumed that there is a single market in each area, and the participation of external players in each market is possible. A market‐based mechanism for power exchange management is designed by a proposed central coordinator entity. In this mechanism, two main roles are considered for the coordinator, namely, the determination of the external network equivalents for each area, and the management of power exchange in an iterative decision‐making process to maintain system security. The designed mechanism uses the proposed power exchange management factors matrix. Then, a market process is run for the management of external player's exchanges. The numerical results for a small‐scale (15‐bus) test system as well as the IEEE RTS‐96 system are presented to demonstrate the effectiveness of the proposed mechanism.
Design of a novel intelligent damping controller for unified power flow controller in power system connected offshore power applications
Authors: Lin Whei‐Min , Lu Kai‐Hung , Ou Ting‐Chia
Published: August 2015

This study proposes a unified power flow controller‐based oscillation damping controller for use with a permanent magnet synchronous generator‐based offshore power farm. A novel intelligent damping controller (NIDC) was used to increase the stability of power control and improves the performance, where the proposed NIDC consists of the adaptive critic network, the functional link‐based Elman neural network (FLENN), the genetic ant colony optimisation algorithm (GACO) and proportional–integral‐derivative (PID) linear damping controller. The PID damping controller analyses complex eigenvalues based on the theory of modern control. The node connecting weights of the FLENN and critic network are trained online. A GACO approach is developed to adjust the learning rates and thus improve the learning ability. The proposed NIDC can achieve better damping characteristics, and the internal power fluctuations can also be effectively alleviated.
Hybrid islanding detection method based on decision tree and positive feedback for distributed generations
Authors: Zhou Bin , Cao Chi , Li Canbing , Cao Yijia , Chen Chen , Li Yong , Zeng Long
Published: August 2015

Islanding detection plays an important role in operation and control of distributed generations (DGs). In this study, a novel hybrid method is proposed, which combines decision tree (DT) with voltage and frequency positive feedbacks for islanding detection in DGs. In the proposed method, the feature indices of prescribed events are captured and recorded in a target location to train a DT classifier, and the classifier can then be used for categorising islanding mode or grid‐connected mode. The voltage and frequency positive feedback schemes are employed to regulate the DG power outputs based on voltage and frequency deviation between DG outputs and rated values. Furthermore, the disturbances are introduced to change the feature indices significantly when DG is switched to islanding mode, which can increase the sensitivities of feature indices and improve detection accuracy. The proposed hybrid method has been fully evaluated and tested on a representative DG system with two DGs. Simulation studies demonstrate that the proposed method can detect the islanding more accurately in situations where the power is balanced between DG output and load consumption, and can also improve detection accuracy in situations where DG system operates in minimum or maximum loading states.