bluuebunny/crossref_metadata_2025 huggingface dataset:
Linear dynamic parameter‐varying sliding manifold for air–fuel ratio control in lean‐burn engines
Authors: Tafreshi Reza , Ebrahimi Behrouz , Mohammadpour Javad , Franchek Matthew A. , Grigoriadis Karolos , Masudi Houshang
Published: August 2013

Precise control of air–fuel ratio (AFR) is one of the most challenging tasks in lean‐burn spark ignition engines control. The main problem arises because of the large time‐varying delay in the engine operating envelope. In this study, a new sliding mode‐based synthesis method is presented to control AFR in order to improve fuel economy and decrease the tailpipe emissions. The time‐varying delay dynamics is first estimated by Padé approximation, which transfers the system into a system with parameter‐varying non‐minimum phase dynamics. Non‐minimum phase characteristics restrict the application of conventional sliding mode control approach because of the unstable internal dynamics. The system dynamics is then rendered into the normal form to investigate the system unstable internal dynamics. A systematic approach is proposed to design a linear dynamic parameter‐varying sliding manifold (LDPVSM) in order to stabilise the unstable internal dynamics according to the desired output tracking error dynamics. Additionally, the proposed LDPVSM provides the system with robustness against unmatched perturbation. The method that can be easily implemented in practical settings exhibits the desired dynamics independent of the matched and unmatched disturbances. The results of applying the proposed method to experimental data demonstrate the closed‐loop system stability and a superior performance against time‐varying delay, canister purge disturbances and measurement noise.
Data‐driven subspace‐based adaptive fault detection for solar power generation systems
Authors: Chen Jianmin , Yang Fuwen
Published: August 2013

Data‐driven fault detection has emerged as one of the most prevalent topics in the fault diagnosis. In this study, a novel data‐driven subspace‐based fault‐detection scheme is proposed to handle the problem of fault detection with system uncertainties in solar power generation systems. A data‐driven subspace‐based predictor is developed by using the input–output measurements. The residual signal is generated from the predictive error of the predictor and a fault‐detection filter that is designed to diminish the influence of system uncertainties. An adaptive algorithm is developed for updating the fault‐detection filter. Faults can be detected by comparing the evaluated residual signal with a threshold. The reliability of the designed fault‐detection scheme is verified in three cases in a solar power generation system.
Design of quantised dynamic output feedback for decentralised ℋ∞ control systems
Authors: Zhai Guisheng , Chen Ning , Gui Weihua
Published: August 2013

The design of quantised dynamic output feedback for decentralised ℋ∞ control systems is considered with multi‐input and multi‐output. It is assumed that a decentralised dynamic output feedback has been designed for a decentralised continuous‐time LTI system, so that the closed‐loop system is stable and a desired ℋ∞ disturbance attenuation level is achieved, and that each channel's measurement outputs are quantised before they are passed to the local controller. We propose a local‐output‐dependent strategy for updating the quantisers’ parameters, so that the overall closed‐loop system is asymptotically stable and achieves the same ℋ∞ disturbance attenuation level. Both the pre‐designed controllers and the quantisers’ parameters are constructed in a decentralised manner, depending on local measurement outputs.
Neural networks impedance control of robots interacting with environments
Authors: Li Yanan , Ge Shuzhi Sam , Zhang Qun , Lee Tong Heng
Published: August 2013

In this study, neural networks (NN) impedance control is proposed for robot–environment interaction. Iterative learning control is developed to make the robot dynamics follow a given target impedance model. To cope with the problem of unknown robot dynamics, NN are employed such that neither the robot structure nor the physical parameters are required for the control design. The stability and performance of the resulted closed‐loop system are discussed through rigorous analysis and extensive remarks. The validity and feasibility of the proposed method are verified through simulation studies.
Distributed formation control of mobile autonomous agents using relative position measurements
Authors: He Fenghua , Wang Ye , Yao Yu , Wang Long , Chen Weishan
Published: August 2013

In this study, we consider an acyclic rigid formation with a group of mobile autonomous agents moving in a two‐dimensional space. The formation is generated via a Henneberg sequence construction in which there is one global leader that does not follow any other agents, one first‐follower that only follows the global leader, and each of other agents has two leaders, which is added by a vertex addition or an edge splitting operation. The entire formation moves with the leadership of the global leader. Every follower agent tries to maintain distances towards its leaders. Under the constraint of the acceleration for the global leader, the distributed formation control laws are proposed for the followers that only use the locally relative distance measurement. The control law of the first‐follower is proposed, which needs to know the velocity of the global leader and the relative distance between the global leader and itself. The global asymptotic stability of the expected formation is proved via a Lyapunov‐based technique for the considered multi‐agent system. Moreover, the stable rigidity problem of a formation is investigated for the proposed distributed relative position‐only formation control law. Necessary and sufficient conditions are provided that must be satisfied by the architecture of the underlying graph. Simulation results illustrate the effectiveness of the proposed formation control approach.
Finite‐time tracking for double‐integrator multi‐agent systems with bounded control input
Authors: Lu Xiaoqing , Chen Shihua , Lü Jinhu
Published: August 2013

This study investigates the finite‐time tracking for double‐integrator multi‐agent systems with bounded control input under the conditions of fixed and switching jointly reachable digraphes. In detail, two continuous distributed tracking protocols are designed to track the virtual leader in finite time with the same velocity and converging position. In particular, one introduces a special continuous distributed tracking protocol with bounded control input to track the virtual leader in finite time and reduce the chatter together. An example is also given to validate the proposed approaches.
Control for a class of non‐linear singularly perturbed systems subject to actuator saturation
Authors: Zhou Linna , Yang Chunyu , Zhang Weidong
Published: August 2013

This study considers the control problem for a class of non‐linear singularly perturbed systems (SPSs) subject to actuator saturation. A sufficient condition for the existence of state‐feedback controllers to achieve a prescribed stability bound is proposed and the corresponding basin of attraction is estimated. Then a convex optimisation problem is formulated, by which an optimal controller can be obtained to achieve a prescribed stability bound and simultaneously maximise the estimate of the basin of attraction of the SPSs for any allowable singular perturbation parameter. Furthermore, a stability condition is established, which improves the existing stability bound analysis methods for a class of non‐linear SPSs. Finally, examples are given to show the advantages and effectiveness of the obtained results.
Observability analysis and observer design for finite automata via matrix approach
Authors: Xiangru Xu , Yiguang Hong
Published: August 2013

This study investigates the observability problem and the observer design of partially observed finite automata via a matrix approach. Using semi‐tensor product of matrices, finite automata are modelled in the form of discrete‐time bilinear systems. Matrix‐form necessary and sufficient conditions for both the initial and current state observability, either with or without input information, are first proposed. Based on that, a constructive method for the observer design is provided.
Fault‐tolerant control of strict‐feedback non‐linear time‐delay systems with prescribed performance
Authors: Yoo Sung Jin
Published: August 2013

An approximation‐based adaptive fault‐tolerant (AFT) control problem is investigated for strict‐feedback non‐linear systems with unknown time‐delayed non‐linear faults. The error surfaces restricted by prescribed performance bounds are employed to guarantee the transient performance at the moment when faults with unknown occurrence time and magnitude occur. Based on the surfaces, we design a memoryless AFT control system where the function approximation technique using neural networks is applied to adaptively approximate unknown non‐linear effects and changes in model dynamics because of the time‐delayed faults. It is shown from Lyapunov stability theorem that the tracking error of the proposed control system is preserved within the prescribed performance bound and converges to an adjustable neighbourhood of the origin regardless of unknown time‐delayed non‐linear faults.
Vehicle platoon and obstacle avoidance: a reactive agent approach
Authors: Dafflon Baudouin , Gechter Franck , Gruer Pablo , Koukam Abderrafiaa
Published: August 2013

Reactive multi‐agent systems are increasingly applied to problem solving, modelling and simulation. Among the benefits of this approach, there is the capability to solve complex problems, whereas maintaining functional and conceptual simplicity of involved entities. Many examples have shown that approaches based on multi‐agent systems are effective in solving complex problems such as life simulation and multi‐robot cooperation for instance. Side‐by‐side vehicle platoon systems, which are studied in this article, can be adopted as a representative example of this class of applications. Based on preceding works, this study presents a local platoon control approach with obstacle avoidance. The proposed vehicle decision‐making process is considered as a multi‐agent system, the agents of which make collectively the best decision considering the perceived constraints and the preceding vehicle position and speed.
Statistical traffic state analysis in large‐scale transportation networks using locality‐preserving non‐negative matrix factorisation
Authors: Han Yufei , Moutarde Fabien
Published: August 2013

Statistical traffic data analysis is a hot topic in traffic management and control. In this field, current research progresses focus on analysing traffic flows of individual links or local regions in a transportation network. Less attention are paid to the global view of traffic states over the entire network, which is important for modelling large‐scale traffic scenes. Our aim is precisely to propose a new methodology for extracting spatiotemporal traffic patterns, ultimately for modelling large‐scale traffic dynamics, and long‐term traffic forecasting. The authors attack this issue by utilising locality‐preserving non‐negative matrix factorisation (LPNMF) to derive low‐dimensional representation of network‐level traffic states. Clustering is performed on the compact LPNMF projections to unveil typical spatial patterns and temporal dynamics of network‐level traffic states. The authors have tested the proposed method on simulated traffic data generated for a large‐scale road network, and reported experimental results validate the ability of our approach for extracting meaningful large‐scale space‐time traffic patterns. Furthermore, the derived clustering results provide an intuitive understanding of spatial‐temporal characteristics of traffic flows in the large‐scale network and a basis for potential long‐term forecasting.
Applications of real‐time speed control in rail‐bound public transportation systems
Authors: Albrecht Thomas , Binder Anne , Gassel Christian
Published: August 2013

This study gives an overview on applications of speed optimisation as one control measure for intelligent traffic management in rail‐bound public transportation systems. The concept of operational target points and target windows is introduced. Speed and dwell time control are used to reach these targets, thereby improve throughput through system‐related bottlenecks and reduce energy consumption. Different rail‐bound transportation systems are compared and requirements for the application of speed control are derived. Case studies for three different rail‐bound passenger transportation systems are presented that demonstrate the potential effects of these control methods on energy consumption and timetable deviation. These control strategies can be implemented using driver advisory systems (DAS) or fully automatic train operation (ATO).
Real‐time estimation of travel speed using urban traffic information system and filtering algorithm
Authors: Ahn Gye‐Hyeong , Ki Yong‐Kul , Kim Eun‐Jeong
Published: August 2013

Travel speed is an important parameter for measuring road traffic. urban traffic information system (UTIS) was developed as a mobile detector for measuring link travel speeds in South Korea. However, UTIS incur errors, such as those caused by irregular vehicle trajectories and communication delays. This study describes an algorithm developed for estimating reliable and accurate average roadway link travel speeds using UTIS data. The algorithm estimates link travel times using a robust data‐filtering procedure to identify valid observations within a sampling interval using a varying data validity window. The size of the data validity window varies as a function of the standard deviation of observations in previous intervals. A field test showed that the variance of the percent errors of link travel times was reduced when measured using the new model. Therefore it can be concluded that the proposed model significantly improves travel speed measuring accuracy.
Anticipatory traveller information system for freeway‐arterial networks
Authors: Xu Tiandong , Hao Yuan , Peng Zhongren , Sun Lijun
Published: August 2013

Anticipatory traveller information system based on variable message sign (VMS) aims to relieve recurrent and non‐recurrent congestion by using predicted traffic conditions to design control strategies consistent with drivers’ route choice behaviour to guide drivers through the freeway‐arterial networks and improve system performance. To provide anticipatory traveller information consistent with drivers’ en‐route diversion behaviour and controller's objectives effectively, this study examines (i) automated calibration of the parameters of a time‐variant drivers’ en‐route diversion model using aggregate‐level data, and (ii) an active route guidance scheme, which projects the network states into the near future and determines spatiotemporal coordinated anticipatory traveller information. The proposed system is tested on real world networks. The implementation results demonstrate that the anticipatory traveller information provided by the proposed model is more consistent, and therefore easier to be accepted by drivers. The findings also reveal that the coordinated VMS‐based anticipatory traveller information effectively provides guidance to drivers because it accounts for the spatial and temporal changes in traffic conditions, and encourages better use of roadway capacity, thereby resulting in better system performance over the same period of operations.
Reported use of speed control systems: cruise control and speed limiter
Authors: Pereira Marta , Bruyas Marie‐Pierre , Kaufmann Clemens , Britschgi Virpi , Gil José Luis Diez , Zaoral Aleš
Published: August 2013

This study presents results from focus group sessions conducted in six countries, namely, Austria, Czech Republic, Finland, France, Portugal and Spain. The work was conducted within the framework of the European project INTERACTION, and the main aim was to collect the opinions of drivers that had cruise control and speed limiter systems available for more than 1 year. A constant comparison analysis was performed and content categories compared among the sessions. This technique allowed assessing whether themes that emerged from one group also emerged in another. Results provide insights into the motives underlying system use and their effects on driving behaviour. A higher percentage of drivers reported using cruise control more frequently than speed limiter. Moreover, drivers having both systems used cruise control significantly more than speed limiter. Statements of ‘dislike’ were documented for speed limiter in several group sessions. Although drivers had the systems available for more than 1 year, lack of knowledge regarding specific system functioning was apparent. Reports of trial‐and‐error learning in real driving conditions, experience of critical situations and performance of secondary tasks with both systems active are discussed in this study.
Simple method for camera calibration of roundabout traffic scenes using a single circle
Authors: Dinh Hai , Tang Hua
Published: August 2013

In this study, the authors present a simple method to estimate intrinsic and extrinsic parameters of the camera for roundabout traffic scenes. Unlike many previous works on camera calibration for roadway scenes by using parallel lines, the proposed work addresses camera calibration for roundabout scenes by using a circle. The proposed method can estimate focal length, pan angle, tilt angle and camera height by matching the ellipse equation extracted from an image with the perspective‐transformed equation of the corresponding real‐world circle. This method requires only one image for camera calibration. The method is validated with real‐world roundabout traffic scenes and the calibration results are reasonably accurate compared with ground truth measurements.
Design, implementation and optimisation of an energy harvesting system for vehicular ad hoc networks’ road side units
Authors: Ibrahim Qutaiba
Published: August 2013

Vehicular ad hoc network (VANET) research has spanned a wide variety of topics in recent years. This study deals with a subject rarely discussed in the literatures, the design procedure of a road side unit (RSU) armed with solar energy‐harvesting circuit and its power management module. Embedded UBICOM IP2022 platform was adopted to implement the intended RSU. A complete design steps of the electronic circuit were described and the necessary values of the system component, that is, solar cell panels, battery cells and the DC‐DC converter was tuned to suite the design goals. In order to decrease the power consumption of the suggested RSU and to extend the lifetime of the batteries, a power management module based on an artificial neural network and green scheduler was suggested. This scheduler is located in the control centre and composed of three algorithms in order of execution: the prediction, ON/OFF and evaluation algorithms. The adoption of the green scheduler reduces the power consumption of the nodes, which extends the battery life and decreases the number of the required battery cells.
Machine‐learning methodology for energy efficient routing
Authors: Masikos Michail , Demestichas Konstantinos , Adamopoulou Evgenia , Theologou Michael
Published: August 2013

Eco‐driving assistance systems encourage economical driving behaviour and support the driver in optimising his/her driving style to achieve fuel economy and consequently, emission reductions. Energy efficiency is also one of the most pertinent issues related to the autonomy of fully electric vehicles. This study introduces a novel methodology for energy efficient routing, based on the realisation of dependable energy consumption predictions for the various road segments constituting an actual or potential vehicle route, performed mainly by means of machine‐learning functionality. This proposed innovative methodology, the functional architecture implementing it, as well as demonstrative experimental results are presented in this study.
Localisation of multiple faults in motorcycles based on the wavelet packet analysis of the produced sounds
Authors: Anami Basavaraj S. , Pagi Veerappa B.
Published: August 2013

Service station experts examine the sound patterns of the motorcycles to diagnose the faults. Automatic fault diagnosis is a challenging task and more so is recognition of multiple faults. This study presents a methodology for localisation of multiple faults in motorcycles. The sound signatures of multiple faults are constructed by fusing the individual signatures of faults from engine and exhaust subsystems. Energy distributions in the approximation coefficients of wavelet packets are used as features. Among the classifiers used, artificial neural network is found suitable for detecting the presence of multiple faults. The recognition accuracy is over 78% when trained with individual fault signatures and over 88% when trained with combined fault signatures.
Missing traffic data: comparison of imputation methods
Authors: Li Yuebiao , Li Zhiheng , Li Li
Published: August 2013

Many traffic management and control applications require highly complete and accurate data of traffic flow. However, because of various reasons such as sensor failure or transmission error, it is common that some traffic flow data are lost. As a result, various methods were proposed by using a wide spectrum of techniques to estimate missing traffic data in the last two decades. Generally, these missing data imputation methods can be categorised into three kinds: prediction methods, interpolation methods and statistical learning methods. To assess their performance, these methods are compared from different aspects in this paper, including reconstruction errors, statistical behaviours and running speeds. Results show that statistical learning methods are more effective than the other two kinds of imputation methods when data of a single detector is utilised. Among various methods, the probabilistic principal component analysis (PPCA) yields best performance in all aspects. Numerical tests demonstrate that PPCA can be used to impute data online before making further analysis (e.g. make traffic prediction) and is robust to weather changes.
Energy storage systems impact on the short‐term frequency stability of distributed autonomous microgrids, an analysis using aggregate models
Authors: Serban Ioan , Teodorescu Remus , Marinescu Corneliu
Published: August 2013

This study analyses the integration impact of battery energy storage systems (BESSs) on the short‐term frequency control in autonomous microgrids (MGs). Short‐term frequency stability relates with the primary or speed control level, as defined in the regulations of the classical grids. The focus is on autonomous MGs that dynamically behave similarly to the classical power systems. This is the systems case with classical distributed generators (DGs), but which can also contain renewable energy sources (RESs) in a certain penetration level. During MG islanded operation, the local generators take over most of the frequency control process, by means of their automatic generation control, which include inertia response and primary control. However, RES‐based DGs are rarely able to provide grid frequency support, as they lack controllability and usually the power conversion chain does not have the possibility of storing and releasing energy when required by the system. Therefore the need of boosting the MG power reserves by adding energy storage systems is often a requirement. The study highlights the improvement in the MG short‐term frequency stability brought by an original BESS control structure enhanced with both inertial response and an adaptive droop characteristic during battery state‐of‐charge limitations. The conducted analysis is accomplished by adopting aggregated models for the involved control mechanisms. The developed model is analysed in frequency domain, whereas an experimental test bench including a real‐time digital simulator with BESS controller in a hardware‐in‐the‐loop structure is used for assessing the system performances.
Power oscillation damping capabilities of wind power plant with full converter wind turbines considering its distributed and modular characteristics
Authors: Knüppel Thyge , Nielsen Jørgen N. , Jensen Kim H. , Dixon Andrew , Østergaard Jacob
Published: August 2013

Wind power plants (WPP) are for power system stability studies often represented with aggregated models where several wind turbines (WT) are aggregated into a single up‐scaled model. The advantage is a reduction in the model complexity and the computational time, and for a number of study types the accuracy of the results has been found acceptable. A large WPP is, however, both modular and distributed over a large geographical area, and feasibility of aggregating the WTs, thus, have to be reassessed when new applications are introduced for WPPs. Here, the power oscillation damping capabilities are investigated for a WPP, which includes the full layout of the collector grid and where the WTs are represented individually. With this approach, the influence of the WT control in terms of impact on oscillatory modes is assessed for the WTs individually. The initial results encourage that park level control is possible. Time domain simulations support that each WT contribute to a common WPP response. Park level active and reactive power‐based power oscillation damping controllers (POD) are designed and the positive damping contribution is demonstrated. Keeping the POD designs unchanged, the impact of WPP aggregation is investigated and it is shown that the level of WPP aggregation only has limited impact on the resulting modal damping. The study is based on a non‐linear, dynamic model of the 3.6 MW Siemens Wind Power WT.
Rigorous model for evaluating wind power capacity credit
Authors: Zhang Ning , Kang Chongqing , Kirschen Daniel S. , Xia Qing
Published: August 2013

How much capacity credit should be given to wind power in generation system adequacy analysis is a question of great interest around the world. Both a theoretical analysis and an accurate evaluation on the wind power capacity credit are essential for understanding its contribution to power system reliability. Current evaluation techniques usually rely on numerical calculation procedures that do not provide an analytical analysis, or are based on assumptions that are valid only for small wind penetration. This study presents a rigorous model based on the definition of the reliability function. The derivation of the model is presented and a fast and accurate method for calculating the capacity credit is developed based on this model. The proposed method does not require strong hypotheses and is thus widely applicable, especially when current evaluation techniques might cause large errors, for example, when the wind power penetration is large and the wind power and load profile are not statistically independent. The model is used to explain how the statistical characteristics of the load and wind power affect the capacity credit, from both a statistical and chronological perspective. Numerical tests demonstrate the correctness of the proposed model and its potential applicability under different circumstances.
Analysis, design and testing of a novel direct‐drive wave energy converter system
Authors: Crozier Richard , Bailey Helen , Mueller Markus , Spooner Edward , McKeever Paul
Published: August 2013

A coupled electromechanical and hydrodynamic time‐domain simulation of a direct‐drive generator connected to a heaving buoy for wave energy conversion is presented. The system is based on a novel direct‐drive power take‐off unit referred to as snapper. The simulation is based primarily in MATLAB using its built‐in ordinary differential equation solvers. These solvers act on the data derived from electromagnetic finite element analysis and from the WAMIT wave interaction simulation software. Test results of a generator prototype for comparison with the electromechanical simulation are presented. Results from wave tank tests of a full system incorporating the power take‐off are also provided for comparison with the hydrodynamic model.
Wind energy conversion into electricity by means of the rectifier with near sinusoidal input current‐1 converter
Authors: Alexa Dimitrie , Pletea Irinel Valentin , Sirbu Adriana , Lazar Alexandru
Published: August 2013

The study presents a wind generator system based on a new converter configuration with a rectifier with near sinusoidal input currents (RNSICs‐1 converter with DC capacitors connected in parallel with diodes). A detailed analysis of the system for different values of the load current is presented and the advantages of the solution are emphasised. The new converter configuration is characterised by smaller power losses, reduced electromagnetic interference (EMI) problems, low harmonic input currents, high reliability, as well as reduced costs. This original configuration could also be used for small hydro interconnection with squirrel cage induction generator (SCIG) and partial variable‐speed wind turbine (typically 60–100% synchronous speed).
Assessing the economic benefit of a bidding decision support tool for wind power producers
Authors: Moreno Maria Ángeles , Usaola Julio , Bueno Miriam
Published: August 2013

This document describes the assessment of a decision support tool for wind power producers in real wind farms. This tool allows them to update their positions taken in daily markets into subsequent adjustment markets. The tool intends to maximise the revenues of wind power producers that participate in electricity markets through an optimisation procedure, making use of the possibilities of non‐continuous adjustment markets and the probabilistic tools developed in the EU project ANEMOS.plus. Results are presented for nine Spanish wind farms and they are compared with those obtained with a standard strategy of market participation for wind power producers. For the examined cases, the revenues were overall increased in a 1.3% by using the decision support tool. This could encourage even more the participation of wind energy in electricity markets. The overall energy imbalance also increases, showing a potential risk for the whole system if all wind power producers would use such a tool.
Intelligent controlled three‐phase squirrel‐cage induction generator system using wavelet fuzzy neural network for wind power
Authors: Lin Faa‐Jeng , Tan Kuang‐Hsiung , Fang Dun‐Yi , Lee Yih‐Der
Published: August 2013

An intelligent controlled three‐phase squirrel‐cage induction generator (SCIG) system for grid‐connected wind power application using wavelet fuzzy neural network (WFNN) is proposed in this study. First, the indirect field‐oriented mechanism is implemented for the control of the SCIG system. Then, an AC/DC power converter and a DC/AC power inverter are developed to convert the electric power generated by a three‐phase SCIG from variable‐voltage and variable‐frequency to constant‐voltage and constant‐frequency. Moreover, the intelligent WFNN controller is proposed for both the AC/DC power converter and DC/AC power inverter to improve the transient and steady‐state responses of the SCIG system at different operating conditions. Three online trained WFNNs using backpropagation learning algorithm are implemented as the tracking controllers for the DC‐link voltage of the AC/DC power converter and the active power and reactive power outputs of the DC/AC power inverter. Furthermore, the network structure and the online learning algorithm of the WFNN are introduced in detail. Finally, some experimental results are provided to demonstrate the effectiveness of the proposed SCIG system for wind power.
Breaking wave loads on monopiles for offshore wind turbines and estimation of extreme overturning moment
Authors: Stansby Peter K. , Devaney Louise C. , Stallard Tim J.
Published: August 2013

Measurements of breaking wave forces on vertical circular columns have been re‐analysed, where substantial magnification over forces because of non‐breaking non‐linear waves may occur, by a factor of up to 2.8. The analysis shows that this factor increases as the depth parameter kd decreases, being close to unity for kd > 1.5 (k is the wave number and d is depth). Non‐breaking wave forces are predicted reasonably by non‐linear stream function wave theory using Morison's equation with empirical drag and inertia coefficients. A study was then made of the magnitude of wave overturning moment in relation to hub moment due to wind on standard 2 and 5 MW turbines with a 6 m diameter column. This showed that the wave moment in extreme conditions is greater than wind ‘hub’ moment for depths greater than about 7 and 13 m for the 2 and 5 MW turbines, respectively. Monopiles are normally used in depths below about 30 m and extreme moments due to waves occur when waves are depth‐limited and defined by the Miche criterion, well below the limiting value of kd for the onset of depth‐induced breaking. The maximum moment for these depths is expected to be predicted reasonably.
Performance analysis and testing of a 250 kW medium‐speed brushless doubly‐fed induction generator
Authors: Abdi Ehsan , McMahon Richard , Malliband Paul , Shao Shiyi , Mathekga Mmamolatelo Ezekiel , Tavner Peter , Abdi Salman , Oraee Ashknaz , Long Teng , Tatlow Mark
Published: August 2013

This study presents the performance analysis and testing of a 250 kW medium‐speed brushless doubly‐fed induction generator (DFIG), and its associated power electronics and control systems. The experimental tests confirm the design, and show the system's steady‐state and dynamic performance and grid low‐voltage ride‐through capability. The medium‐speed brushless DFIG in combination with a simplified two‐stage gearbox promises a low‐cost low‐maintenance and reliable drivetrain for wind turbine applications.
Impact of wind power plant reactive current injection during asymmetrical grid faults
Authors: Göksu Ömer , Teodorescu Remus , Bak Claus Leth , Iov Florin , Carne Kjær Philip
Published: August 2013

As more renewable energy sources, especially more wind turbines (WTs) are installed in the power system; grid codes for wind power integration are being generated to sustain stable power system operation with non‐synchronous generation. Common to most of the grid codes, wind power plants (WPPs) are requested to stay connected and inject positive‐sequence reactive current in order to boost positive‐sequence grid voltage during short‐circuit grid faults, irrespective of the fault type; symmetrical or asymmetrical. However, as shown in this study, when WPPs inject pure positive‐sequence reactive current in case of asymmetrical faults, as a conventional method (CM) in accordance with the grid code requirement, positive‐sequence grid voltage is boosted, but also higher negative sequence voltage in the grid and higher overvoltages at the non‐faulty phases occur. In this study, an alternative injection method, where WTs are injecting both positive and negative sequence currents during asymmetrical faults, providing improved grid support, is given and compared with the CM. In addition, effect of coupling between positive, negative and zero sequences when WPPs are injecting currents during asymmetrical faults, is investigated, which was not considered in the wind power impact studies before.
Design and implementation of a droop control in d–q frame for islanded microgrids
Authors: Planas Estefanía , Gil‐de‐Muro Asier , Andreu Jon , Kortabarria Iñigo , de Alegría Iñigo Martínez
Published: August 2013

The droop control method is usually selected when several distributed generators (DGs) are connected in parallel forming an islanded microgrid. This is because of the advantages it offers such as flexibility, absence of critical communications etc. Besides, several studies add a fictitious impedance to improve the performance of the original droop method. However, only a few studies deal with the design of this fictitious impedance, which is necessary to ensure an improvement in the dynamics and stability of the microgrid. In addition, these studies do not consider load variations for the design of the fictitious impedance, which is a habitual event in these systems. On the other hand, some studies propose a restoration control to bring the frequency and voltage amplitude of the microgrid to their nominal values. However, these do not deal with the design of the dynamics of this control to maintain a good transient and to ensure the stable performance of the microgrid. This study proposes the design of a fictitious impedance that ensures the stable operation of an experimental microgrid without power oscillations during load jumps and throughout its entire load range. This study also proposes a new restoration control that allows to take into account the possible inertias, delays etc. of the DGs and reduces the bandwidth of the required communications. Moreover, the proposed restoration control is properly designed to guarantee a good transient and the satisfactory performance of the microgrid. Experimental results confirm the validity of the proposed controls.
Design and implementation of a new portable thermoelectric generator for low geothermal temperatures
Authors: Ahiska Rasit , Mamur Hayati
Published: August 2013

In this study, the design and implementation of a new portable thermoelectric generator of 100 W for low geothermal temperatures has been carried out. For this system, a new SCADA‐based testing and measuring system equipped with special software has been developed and employed for the first time. Thus, effects of the hot–cold water flow rates, the temperature differences between the surfaces and the load resistance affecting output power and efficiency of the thermoelectric generator have been investigated by a single testing and measuring system device. In the established SCADA‐based testing and measuring system, the hot–cold water flows passed throughout the surfaces of the thermoelectric generator were increased by up to 3.7 and 12.8 l/min, respectively. Then, the temperature difference between the surfaces of the thermoelectric generator was measured as 67°C. When the load resistance of the thermoelectric generator was about 15 Ω, the maximum power of the thermoelectric generator was obtained as 41.6 W and the conversion efficiency was calculated as 3.9%. Also, the SCADA‐based testing and measuring system will open up a new stage in examination of various thermoelectric generators.
Wind farm optimal connection to transmission systems considering network reinforcement using cost‐reliability analysis
Authors: Taherkhani Morteza , Hosseini Seyed Hamid
Published: August 2013

In this study, a novel network reinforcement model incorporating optimal wind farms (WFs) integration to power systems is proposed. Based on the reinforcement model, new transmission lines are added to the network for eliminating the transmission network congestion. In addition, a methodology for determining the WFs optimal capacities, the economical WF lines transfer rates and the appropriate reinforcement plan, whereas maximising the total benefit using cost‐reliability analysis is presented. In this way, the objective of the proposed optimisation problem has been divided into a master problem and two subproblems. Benders decomposition is employed to connect the master and subproblems of the model. In order to assess the validity of the proposed method, it is applied to the IEEE 24‐bus test system under three different scenarios.
Analysis and simulation of an Adefovir anti‐hepatitis B virus infection therapy immune model with alanine aminotransferase
Authors: Su Yongmei , Zhao Lei , Min Lequan
Published: August 2013

Hepatitis B virus (HBV) infection models and anti‐HBV infection therapy models have been set up to understand and explain clinical phenomena. Many of these models have been proposed based on Zeuzem et al. and Nowak et al.'s basic virus infection model (BVIM). Some references have pointed out that the basic infection reproductive number of the BVIM is biologically questionable and gave the modified models with standard mass action incidences. This study describes one anti‐HBV therapy immune model with alanine aminotransferase (ALT) based on standard mass action incidences. There are two basic infection reproductive numbers R0 and R1 in the model. It is proved that if R0 < 1 and R1 < 1, the disease free equilibrium is locally and globally asymptotically stable, respectively. For the endemic equilibrium, simulation shows that if R1 > 1, it may be also globally asymptotically stable. Simulations based on clinical data of HBV DNA and ALT can explain some clinical phenomena. Simulations of the correlation between liver cells, HBV DNA, cytotoxic T lymphocytes and ALT are also given.
Development and validation of a simulator for wireless data acquisition in gas turbine engine testing
Authors: Dai Xuewu , Mitchell John E. , Yang Yang , Glover Ian , Sasloglou Konstantinos , Atkinson Robert , Panella Isabella , Strong John , Schiffers Werner , Dutta Partha
Published: August 2013

Owing to its cable‐free deployment, wireless sensor networks (WSNs) have drawn great attention as a new technique for industrial data acquisition. However, the harsh environment of the gas turbine engine provides a number of challenges to deployment of wireless sensors. A definitive study of the impact of harsh environments on WSNs is currently lacking, which represents an obstacle to WSN's deployment in safety‐critical industrial instrumentation and automation. In this study, the authors report the test results of applying WSNs to data acquisition in gas turbine engine testing and the development of a realistic software simulator with the purpose of de‐risking the wireless data transmission technology in a project called WIDAGATE (wireless data acquisition in gas turbine engine testing). This study provides an overview of the simulation platform developed and investigates how small‐scale tests of a WSN deployed on a real engine were used to validate and improve the simulator platform. This work proposes realistic modelling of the physical layer (radio channel) when subject to interference in harsh industry environment during aero‐engine testing. Based on the validated, realistic physical layer model, different medium access control protocols are simulated to demonstrate how this improved simulator can be used to select an appropriate protocol.
Generic correlation model for wireless sensor network applications
Authors: Shakya Rajeev K. , Singh Yatindra N. , Verma Nishchal K.
Published: August 2013

In wireless sensor networks (WSNs) having a high density of sensor nodes, transmitted measurements are spatially correlated, often redundantly whenever an event of interest is detected. In this work, the authors propose a correlation model to enable energy‐efficient methodologies that exploit the spatial correlation at the network and medium access control (MAC) layers. At the network layer, the authors first demonstrate how, through proper tuning of both the sensing range and correlation threshold, WSNs can be partitioned into disjoint correlated clusters without degrading the information reliability, thus enabling significant energy saving. On the other hand, as another contribution, the authors investigate the impacts of correlation between nodes on achieved distortion in the event estimation at the sink. The interactions among various parameters such as distortion constraints, spatial node density, node selection, sensing range and their impacts on the reconstruction performance are quantitatively studied. The authors demonstrate that the same level of distortion constraint can be achieved by selecting fewer nodes. The nodes can be still fewer if they are less spatially correlated. However, the MAC protocols which show distributive effect of this selection needs more study.
Wireless walker dynamometer design and static calibration based on ant colony system
Authors: Xu Rui , Ming Dong , Qiu Shuang , Wang Xin , Qi Hongzhi , Zhang Lixin , Wan Baikun
Published: August 2013

Walker is a widely used mobility aid to improve users’ stability and ambulatory ability. Its dynamometer instrumentation is necessary for quantitative study of basic biomechanics and functional requirements for effective use. How to extract the kinetic demands exactly and without any disturbance to normal gait remains a bottleneck for walker dynamometer design. Based on the force measurement of handle reaction vectors (HRVs) applied to the walker, this study developed a novel strain gauge‐based wireless walker dynamometer system integrated with a static calibration algorithm based on ant colony system (ACS). Compared with the traditional measurement of HRV, the proposed method enhances security and flexibility of walker use by using one wireless data transmission system connecting 12 strain‐gauge bridges mounted on the walker frame with the computer. To improve high‐dimensional calibration performance, an ACS algorithm was employed to optimise the sensitivity weight matrix during calibration. To evaluate force measurement reliability, system performance with ACS algorithm was testified and its mean non‐linearity, mean crosstalk and maximal force measurement accuracy error were found to be 6.88, 6.10 and 7.46%, respectively, which were much better than those of traditional linear calibration methods. This implemented walker dynamometer system may prove to be a reliable tool for measurement of hand loads and description of kinetic analysis of basic walker‐assisted gait.
Intra‐cluster key sharing in hierarchical sensor networks
Authors: Ya‐nan Liu , Jian Wang , He Du , Li‐jun Sha
Published: August 2013

In hierarchical sensor networks, key sharing at the intra‐cluster tier (i.e. how to establish pairwise keys between a sensor and its cluster head) is more challenging than that at inter‐cluster tier. Despite some key management protocols have been proposed, there still lacks both secure and efficient one. In this study, the authors proposed an intra‐cluster key sharing to overcome the security problems nowadays. The analysis proved that this proposed scheme has the following advantages by comparing with other schemes: (i) it is more efficient in saving the storage overheads and communication overheads; (ii) it improves the resilience against node capture attacks during and after initialisation; and (iii) it guarantees 100% connectivity at intra‐cluster communication tier.
Cooperative diversity routing and transmission for wireless sensor networks
Authors: Gharavi Hamid , Hu Bin
Published: August 2013

In this study, the authors present a novel design framework aimed at developing ‘cooperative diversity’ in 802.11‐based wireless sensor networks. The proposed scheme is a combination of a time‐reversed space‐time block code scheme at the physical layer and a cooperative routing protocol at the network layer. The core feature of this architecture is that the multiple routes are capable of assisting the transmission of each other, hence the reliability of ‘all’ the wireless links are enhanced simultaneously by cooperative diversity. This will involve the design of physical layer transmission schemes, medium access protocols and routing strategies. For the latter in particular, the authors present a cooperative routing protocol that is capable of exploiting full transmit diversity in wireless sensor networks. The authors restrict ourselves by imposing as few modifications to existing schemes as possible, so that integration to the existing infrastructure will be straightforward. Comprehensive simulations have been carried out to demonstrate the end‐to‐end performance of the proposed scheme. It is shown that a substantial gain can be achieved by cooperative diversity using a virtual multiple input multiple output system architecture.