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  • Journal article
    Scarciotti G, Astolfi A, 2016,

    Moment-based discontinuous phasor transform and its application tothe steady-state analysis of inverters and wireless power transfersystems

    , IEEE Transactions on Power Electronics, Vol: 31, Pages: 8448-8460, ISSN: 0885-8993

    Power electronic devices are inherently discontinuous systems. Square waves, produced by interconnected transistors, are commonly used to control inverters. This paper proposes a novel phasor transform, based on the theory of moments, which allows to analyze the steady-state behavior of discontinuous power electronic devices in closed-form, i.e. without approximations. In the first part of the paper it is shown that the phasors of an electric circuit are the moments on the imaginary axis of the linear system describing the circuit. Exploiting this observation, in the second part of the paper, we focus on the analysis of circuits powered by discontinuous sources. The new “discontinuous phasor transform” is defined and the v-i characteristics for inductors, capacitors and resistors are described in terms of this new phasor transform. Since the new quantities maintain their physical meaning, the instantaneous power and average power can be computed in the phasor domain. The analytic potential of the new tool is illustrated studying the steady-state response of power inverters and of wireless power transfer systems with non-ideal switches.

  • Conference paper
    Chaffey GP, Green TC, 2017,

    Low speed protection methodology for a symmetrical monopolar HVDC network

    , 13th IET International Conference on AC and DC Power Transmission 2017., Publisher: IET

    Protecting a future HVDC network from shortcircuit DC faults is presently expected to require extensive imple-mentation of fast HVDC circuit breakers, allowing for rapid faultisolation. The requirement for circuit breakers may, however, bereduced or removed depending on the protection methodology,resulting in a slower post-fault recovery. The expected faultresponse and the subsequent network recovery is dependenton the circuit breaker, network, and converter configurations.This paper examines a low speed protection methodology fora symmetrical monopolar HVDC system, a configuration whichrequires pole to pole balancing following a pole to ground fault.The fault clearance and network recovery timings are thereforeevaluated for both pole to pole and pole to ground faults onseveral case study networks.

  • Journal article
    Chang H, Moog C, Astolfi A, 2016,

    Occurrence of HIV eradication for preexposure prophylaxis treatment with a deterministic HIV model

    , IET Systems Biology, Vol: 10, Pages: 237-243, ISSN: 1751-8857

    The authors examine the human immunodeficiency virus (HIV) eradication in this study using a mathematical model and analyse the occurrence of virus eradication during the early stage of infection. To this end they use a deterministic HIV-infection model, modify it to describe the pharmacological dynamics of antiretroviral HIV drugs, and consider the clinical experimental results of preexposure prophylaxis HIV treatment. They also use numerical simulation to model the experimental scenario, thereby supporting the clinical results with a model-based explanation. The study results indicate that the protocol employed in the experiment can eradicate HIV in infected patients at the early stage of the infection.

  • Conference paper
    Nduka OS, Pal BC, 2016,

    Harmonic characterisation model of grid interactive photovoltaic systems

    , 2016 IEEE International Conference on Power System Technology (POWERCON), Publisher: IEEE

    This paper presents an alternative model of a grid interactive photovoltaic (PV) system which can be used for characterising the harmonics from a PV system when connected to a distorted and undistorted network respectively. The approach uses an orthogonal series function in modelling the different sections of a practical PV system thus yielding a complete harmonic domain model. The proposed model accurately handles the harmonic cross-coupling between the PV system and the network. Both single and three phase grid interactive single-stage transformerless PV systems are presented. Simulation results show the effectiveness of the proposed model.

  • Journal article
    Konstantelos I, Pudjianto D, Strbac G, De Decker J, Joseph P, Flament A, Kreutzkamp P, Genoese F, Rehfeldt L, Wallasch A, Gerdes G, Jafar M, Yongtao Y, Tidemand N, Jansen J, Nieuwenhout F, van der Welle A, Veum Ket al., 2016,

    Integrated North Sea grids: The costs, the benefits and their distribution between countries

    , Energy Policy, Vol: 101, Pages: 28-41, ISSN: 0301-4215

    A large number of offshore wind farms and interconnectors are expected to be constructed in the North Searegion over the coming decades, creating substantial opportunities for the deployment of integrated networksolutions. Creating interconnected offshore grids that combine cross-border links and connections of offshoreplants to shore offers multiple economic and environmental advantages for Europe's energy system. However,despite evidence that integrated solutions can be more beneficial than traditional radial connection practices, nosuch projects have been deployed yet. In this paper we quantify costs and benefits of integrated projects andinvestigate to which extent the cost-benefit sharing mechanism between participating countries can impede orencourage the development of integrated projects. Three concrete interconnection case studies in the North Seaarea are analysed in detail using a national-level power system model. Model outputs are used to compute thenet benefit of all involved stakeholders under different allocation schemes. Given the asymmetric distribution ofcosts and benefits, we recommend to consistently apply the Positive Net Benefit Differential mechanism as astarting point for negotiations on the financial closure of investments in integrated offshore infrastructure.

  • Journal article
    Vinter RB, Boccia A, Pinho M, 2016,

    Optimal Control Problems with Mixed and Pure State Constraints

    , SIAM Journal on Control and Optimization, Vol: 54, Pages: 3061-3083, ISSN: 0363-0129

    This paper provides necessary conditions of optimality for optimal control problems, in whichthe pathwise constraints comprise both ‘pure’ constraints on the state variable and also ‘mixed’constraints on control and state variables. The proofs are along the lines of earlier analysis formixed constraint problems, according to which Clarke’s theory of ‘stratified’ necessary conditions isapplied to a modified optimal control problem resulting from absorbing the mixed constraint into thedynamics; the difference here is that necessary conditions which now take account of the presenceof pure state constraints are applied to the modified problem. Necessary conditions are given for arather general formulation of the problem containing both forms of the constraints, and then theseare specialized to apply to problems having special structure. While combined pure state and mixedcontrol/state problems have been previously treated in the literature, the necessary conditions in thispaper are proved under less restrictive hypotheses and for novel formulations of the constraints.

  • Journal article
    Forni P, Angeli D, 2016,

    Input-to-state stability for cascade systems with multiple invariant sets

    , Systems and Control Letters, Vol: 98, Pages: 97-110, ISSN: 1872-7956

    In a recent paper Angeli and Efimov (2015), the notion of Input-to-State Stability (ISS) has been generalized for systems with decomposable invariant sets and evolving on Riemannian manifolds. In this work, we analyze the cascade interconnection of such ISS systems and we characterize the finest possible decomposition of its invariant set for three different scenarios: 1. the driving system exhibits multistability (convergence to fixed points only); 2. the driving system exhibits multi-almost periodicity (convergence to fixed points as well as periodic and almost-periodic orbits) and the driven system is assumed to be incremental ISS; 3. the driving system exhibits multiperiodicity (convergence to fixed points and periodic orbits) whereas the driven system is ISS in the sense of Angeli and Efimov (2015). Furthermore, we provide marginal results on the backward/forward asymptotic behavior of incremental ISS systems and on the response of a contractive system under asymptotically almost-periodic forcing. Three examples illustrate the potentiality of the proposed framework.

  • Conference paper
    Beddard A, Wang W, Barnes M, Green TC, Green PRet al., 2016,

    Impact of Parameter Uncertainty on Power Flow accuracy in multi-terminal systems

    , IEEE Power and Energy Society General Meeting 2016, Publisher: IEEE, ISSN: 1944-9925

    Accurate power flow in a MT system can be achievedwith droop controllers. However, almost all publications haveassumed that the DC voltage, DC current and DC cableresistances can be measured with 100% accuracy. In this paper, anovel power flow solver is developed which enables the user toanalyse the impact of these parameters on power flow accuracy.The developed Parameter Uncertainty Power Flow Solver (PUPFS)is shown to be able to accurately calculate the power flowerror for hundreds of parameter uncertainty scenarios in lessthan a second. The PU-PFS is employed to investigate the impactof parameter uncertainty on a potential MT system and theresults show that realistic measurement errors (0.2%) can resultin significant power flow error (>150MW). Finally, the paperassesses the key factors which influence the power flow accuracyresulting in a number of important conclusions.

  • Conference paper
    Nanchian SN, Majumdar AM, Pal BP, 2016,

    Three-phase state estimation using hybrid particle swarm optimization

    , IEEE PES General Meeting 2016, Publisher: IEEE

    This paper proposes a method for three-phase state estimation (SE) in power distribution network including onload tap changers (OLTC) for voltage control. The OLTC tap positions are essentially discrete variables from the SE point of view. Estimation of these variables in SE presents a formidable challenge. The proposed methodology combines discrete and continuous state variables (voltage magnitudes, angles, and tap positions). A hybrid particle swarm optimization (HPSO) is applied to obtain the solution. The method is tested on standard IEEE 13- and 123-bus unbalanced test system models. The proposed algorithm accurately estimates the network bus voltage magnitudes and angles, and discrete tap values. The HPSO-based tap estimation provides a more accurate estimation of losses in the network, which helps in fair allocation of cost of losses in arriving at overall cost of electricity.

  • Conference paper
    Martınez-Sanz IM, Chaudhuri B, Junyent-Ferre A, Trovato V, Strbac Get al., 2016,

    Distributed vs. Concentrated Rapid Frequency Response Provision in Future Great Britain System

    , IEEE Power and Energy Society General Meeting, Publisher: IEEE, ISSN: 1944-9933

    Two major sources of rapid frequency response(RFR) to counter the reducing system inertia problem of theGreat Britain (GB) system are “synthetic inertia” from windturbines and fast demand response (FDR). In this paper, weconsider a future low inertia scenario to show the effectivenessof RFR provision from the large offshore wind farms (OWFs)planned in the North Sea (concentrated response) against FDRfrom loads spread across the GB system (distributed response).The spatial variation in transient frequencies, which can bepronounced in the aftermath of a disturbance and is criticalfor the response activation of these actuators, is accounted. Casestudies using a reduced GB system model show the effectivenessof distributed FDR and concentrated support from OWFs inproviding RFR when disturbances occur in different areas of thesystem where different inertia levels are present.

  • Conference paper
    Chakravorty D, Akhtar Z, Chaudhuri B, Hui SYRet al., 2016,

    Comparison of Primary Frequency Control Using Two Smart Load Types

    , IEEE Power and Energy Society General Meeting, Publisher: IEEE, ISSN: 1944-9933

    Primary frequency control using smart loads withreactive only compensation (SLQ) has been shown in the past.In this paper, further improvement in frequency regulation isshown using smart loads with a back-to-back converter (SLBC)arrangement. This introduces additional flexibility and thereby,allows independent and wider control over active and reactivepower consumption of the smart load. The improvement infrequency regulation with SLBCs is compared against SLQsthrough two separate case studies on 4-generator, 2-area testsystem and also the 39-bus New-England test system. A futurescenario with reduced system inertia is considered for both casestudies. Unlike previous exercises involving smart loads, in thisstudy a detailed representation is used for both the multi-machinetransmission system and the distribution networks down to themedium voltage (MV) level where the smart loads (SLBC/SLQ)are connected. This avoids the inaccuracies associated with loadaggregation or use of system equivalents wherein the networkconstraints, spatial voltage variations etc. are not capturedproperly.

  • Conference paper
    Ge M, Kerrigan EC, 2016,

    Short-term ocean wave forecasting using an autoregressive moving average model

    , Control 2016 - 11th International Conference on Control, Publisher: IEEE

    In order to predict future observations of a noisedrivensystem, we have to find a model that exactly or atleast approximately describes the behavior of the system sothat the current system state can be recovered from pastobservations. However, sometimes it is very difficult to modela system accurately, such as real ocean waves. It is thereforeparticularly interesting to analyze ocean wave properties inthe time-domain using autoregressive moving average (ARMA)models. Two ARMA/AR based models and their equivalent statespace representations will be used for predicting future oceanwave elevations, where unknown parameters will be determinedusing linear least squares and auto-covariance least squaresalgorithms. Compared to existing wave prediction methods, inthis paper (i) an ARMA model is used to enhance the predictionperformance, (ii) noise covariances in the ARMA/AR model arecomputed rather than guessed and (iii) we show that, in practice,low pass filtering of historical wave data does not improve theforecasting results.

  • Conference paper
    Boem F, Sabattini L, Secchi C, 2016,

    Decentralized fault diagnosis for heterogeneous multi-agent systems

    , SysTol’16: 3rd International Conference on Control and Fault-Tolerant Systems, Publisher: IEEE

    The paper proposes a decentralized method forfault detection and isolation in heterogeneous multi-agentssystems. The agents are partitioned into independent nodes,providing the control inputs and monitoring the system, anddependent nodes, controlled by local interaction laws and sub-ject to faults. The approach uses a decentralized state estimationalgorithm allowing the independent nodes to estimate both thestate of the dependent nodes and the control input componentscomputed by the other independent nodes, in a completelydecentralized way, without requiring communication amongthe independent nodes. Suitable detection and isolation resid-uals and thresholds are derived. Detectability and isolabilitysufficient conditions are provided. Simulation results show theeffectiveness of the proposed approach.

  • Journal article
    Ahmad MI, Benner P, Jaimoukha I, 2016,

    Krylov subspace methods for model reduction of quadratic-bilinear systems

    , IET Control Theory and Applications, Vol: 10, Pages: 2010-2018, ISSN: 1751-8644

    The authors propose a two sided moment matching method for model reduction of quadratic-bilinear descriptor systems. The goal is to approximate some of the generalised transfer functions that appear in the input–output representation of the non-linear system. Existing techniques achieve this by utilising moment matching for the first two generalised transfer functions. In this study, they derive an equivalent representation that simplifies the structure of the generalised transfer functions. This allows them to extend the idea of two sided moment matching to higher subsystems which was difficult in the previous approaches. Numerical results are given for some benchmark examples of quadratic-bilinear systems.

  • Journal article
    Calvo JL, Tindemans SH, Strbac G, 2016,

    Incorporating failures of System Protection Schemes into power system operation

    , Sustainable Energy, Grids and Networks, Vol: 8, Pages: 98-110, ISSN: 2352-4677

    Thepower transfer capability of existing transmission networkscan be enhanced through the use of automated system protection schemes (SPS), which rapidly respond to disturbances on the networkto keep the system’s variables within operational bounds. However, reliance on such schemes may expose the network to large impacts –including blackouts –if the SPS does not respond as designed, so the deployment of SPS should balancerisks and benefits.This paper formulates a risk-based cost-benefit framework that allows the operator to strike an optimal balance between constraint costs and risks of demand curtailment due to malfunctioning SPS. It is applied to a simple 4-bus power system inspired by the GB network, for which an exact optimisation problem can be formulated.A component-based dependability model is developed for the SPS to determine its failure modes and associated probabilities. The resulting cost-minimisation problem is solved for a range of operating conditions and SPSreliability levels. The results consistently show cost savings from the use of an SPS, even ifit is highly unreliable, when a hedging strategy may be used. The optimal solution is highly sensitive to the problem parameters, but it is demonstratedthat optimal operational strategies are associated with particular SPS outcomes.This finding may be used as empirical guidance to develop operational strategies for complex networks with unreliable SPS.

  • Conference paper
    Waffenschmidt E, Hui RSY, 2016,

    Virtual inertia with PV inverters using DC-link capacitors

    , EPE 20161 ECCE Europe, Publisher: IEEE

    Soon, virtual inertia for grid control must be covered by photovoltaic inverters. It is suggested to use DC link capacitors for this task. This requires 5 W, 50 J and a capacitor size of about 200 cm 3 per installed kW, corresponding to the size of single phase DC link capacitors. It is shown that the additional power ripple (and thus current ripple) is in the order of 0.1% and the voltage ripple of the intermediate voltage will typically remain between +/-3.6%. The related control can be easily extended by adding a voltage signal to the control voltage, which is proportional to the frequency deviation. Then, the existing controller inherently sets the required additional power fluctuation required for the virtual inertia function.

  • Conference paper
    Judge PD, Merlin MMC, Green TC, Trainer DR, Vershinin Ket al., 2016,

    The augmented trapezoidal alternate arm converter: a power-group augmented DC fault tolerant voltage source converter

    , 2nd International Conference on High Voltage Direct Current

    Achieving DC fault tolerance in modularmultilevel converters requires the use of a significantnumber sub-modules which are capable of generatinga negative voltage. This results in an increase in thenumber of IGBT devices in the current path, resultingin an increase in conduction losses within the converter.This paper introduces a thyristor augmented multilevelstructure called a Power-Group, offering both negativevoltage capability as well as a low conduction loss state,which can be used to construct high efficiency DC faulttolerant converters. When combined with the AlternateArm Converter topology the power-group concept hasbeen found to result in a converter topology that exhibitsvery low power-losses, high quality AC and DC currentwaveforms, while also achieving DC fault tolerance.

  • Journal article
    Teng F, Strbac G, 2016,

    Business cases for energy storage with multiple service provision

    , Journal of Modern Power Systems and Clean Energy, Vol: 4, Pages: 615-625, ISSN: 2196-5625

    Energy storage (ES) has been considered as the key source of flexibility to support the integration of renewable energy. Previous studies have demonstrated the substantial system cost savings by the deployment of ES, including both investment and operation of generation, transmission and distribution infrastructure. However, this societal benefit may not be realized if industry actors do not have a viable business case to appropriately capture these multiple value streams. In this context, this paper investigates the value that ES may deliver to its owner over two specific business cases in a 2030 UK system. Firstly, the application of large-scale ES in the wholesale market is analysed. It is demonstrated that the optimal allocation of ES to provide multiple services is the key element for ES to become competitive in the electricity market. In the second business case, this paper analyses the value of kilowatt-scale ES combined with roof photovoltaic (PV) system in the household and community level. The study shows that multiple service provision of ES through advanced pricing schemes, for example time-of-use (ToU) tariff and dynamic distribution use of system (DUoS), lead to higher value and the coordination in the community level could further justify the application of domestic ES.

  • Journal article
    Kuenzel STK, Assis TML, Pal BC, 2016,

    Impact of Multi-Terminal HVDC Grids onEnhancing Dynamic Power Transfer Capability

    , IEEE Transactions on Power Systems, Vol: 32, Pages: 2652-2662, ISSN: 1558-0679

    This paper proposes the exploitation of MultiTerminalHVDC grids to improve transfer capability in powersystems. Multi-Terminal HVDC systems based on voltagesource converters (VSC-MTDC) have been recognized as apromising alternative for the wind power integration. Under lowwind scenarios, these grids originally dedicated for wind powertransmission can be exploited as an additional interarea transmissionpath, providing extra dynamic security. The paper focuseson small-signal stability assessment, especially in poordamped oscillations associated with interarea modes. Simulationsperformed through a generic computational frameworkhave shown that the high level of flexibility and controllabilityprovided by voltage source converters can considerably improvethe transfer capacity, while preserving adequate dynamic performance.

  • Journal article
    Ge M, Kerrigan EC,

    Noise Covariance Identification for Nonlinear Systems using Expectation Maximization and Moving Horizon Estimation

    , Automatica, ISSN: 0005-1098

    In order to estimate states from a noise-driven state space system, the state estimator requires a priori knowledge of bothprocess and output noise covariances. Unfortunately, noise statistics are usually unknown and have to be determined fromoutput measurements. Current expectation maximization (EM) based algorithms for estimating noise covariances for nonlinearsystems assume the number of additive process and output noise signals are the same as the number of states and outputs,respectively. However, in some applications, the number of additive process noises could be less than the number of states. Inthis paper, a more general nonlinear system is considered by allowing the number of process and output noises to be smaller orequal to the number of states and outputs, respectively. In order to estimate noise covariances, a semi-definite programmingsolver is applied, since an analytical solution is no longer easy to obtain. The expectation step in current EM algorithms relyon state estimates from the extended Kalman filter (EKF) or smoother. However, the instability and divergence problems ofthe EKF could cause the EM algorithm to converge to a local optimum that is far away from true values. We use movinghorizon estimation instead of the EKF/smoother so that the accuracy of the covariance estimation in nonlinear systems canbe significantly improved.

  • Conference paper
    Chiaravalloti F, D'Alfonso L, D'Aquila G, Fedele G, Parisini T, Pin Get al., 2016,

    Finite-time parameters estimation of the Chua system

    , 2nd International Conference on Numerical Computations - Theory and Algorithms (NUMTA), Publisher: American Institute of Physics Publising LLC, ISSN: 1551-7616

    In this work, the unknown set of parameters of the Chua system is recovered under the hypothesys that the voltages of the capacitors are available. To this end, focusing on the differential equations, the Volterra kernel-based approach is used to perform an estimation without the uncertainty of the unmeasurable derivatives and the unknown initial conditions.

  • Conference paper
    Chaffey GP, judge PD, Green TC, 2016,

    Energy Requirements for Modular Circuit Breakers in Multiterminal HVDC Networks

    , HVDC 2016, International Conference on. CSEE, 2016.
  • Journal article
    Lee KW, Moase W, Ooi A, Manzie C, Kerrigan ECet al., 2016,

    Optimization Framework for Codesign of Controlled Aerodynamic Systems

    , AIAA Journal, Vol: 54, Pages: 3149-3159, ISSN: 1533-385X

    Optimization studies of dynamic systems using high-fidelity numerical models necessitate a tradeoff between fidelity and the total computational time required during design. A gradient-based optimization framework is proposed for the aerodynamic shape and controller design of aerodynamic systems using computationally intensive high-fidelity models. Subject to some general properties, the framework offers flexibility in the types of simulation models used and provides guarantees regarding closeness to an optimal design. A nested optimization loop that allows for the partitioning of controller and plant architecture is implemented. The proposed framework exploits time-scale properties of the dynamic system model, closeness properties of partially converged iterative solutions of computational fluid dynamics models, and the continuous adjoint method. It is shown that combining these methods can improve the total computational time relative to finite differencing. An example of optimizing the aerodynamic body and control gains of a tail-fin controlled supersonic missile is presented.

  • Journal article
    Sun M, Konstantelos I, Strbac G, 2016,

    C-Vine copula mixture model for clustering of residential electrical load pattern data

    , IEEE Transactions on Power Systems, Vol: 32, Pages: 2382-2393, ISSN: 0885-8950

    The ongoing deployment of residential smart meters in numerous jurisdictions has led to an influx of electricity consumption data. This information presents a valuable opportunity to suppliers for better understanding their customer base and designing more effective tariff structures. In the past, various clustering methods have been proposed for meaningful customer partitioning. This paper presents a novel finite mixture modeling framework based on C-vine copulas (CVMM) for carrying out consumer categorization. The superiority of the proposed framework lies in the great flexibility of pair copulas towards identifying multi-dimensional dependency structures present in load profiling data. CVMM is compared to other classical methods by using real demand measurements recorded across 2,613 households in a London smart-metering trial. The superior performance of the proposed approach is demonstrated by analyzing four validity indicators. In addition, a decision tree classification module for partitioning new consumers is developed and the improved predictive performance of CVMM compared to existing methods is highlighted. Further case studies are carried out based on different loading conditions and different sets of large numbers of households to demonstrate the advantages and to test the scalability of the proposed method.

  • Journal article
    Pipelzadeh Y, Ray Chaudhuri N, Chaudhuri B, Green TCet al., 2016,

    Coordinated control of offshore wind farm and onshore HVDC converter for effective power oscillation damping

    , IEEE Transactions on Power Systems, Vol: 32, Pages: 1860-1872, ISSN: 1558-0679

    Damping contribution from wind farms (WFs) islikely to become a mandatory requirement as part of the gridcodes. For remote offshore WFs, connected through a voltagesource converter (VSC)-based direct current (DC) link, the mostconvenient option for the onshore transmission system operator(TSO) is to modulate the reactive power at the onshore VSCwithin their own jurisdiction. In this paper, we show thatsupplementary control through the onshore VSC alone, althoughattractive for TSOs, could result in unacceptable voltage variationsin the onshore power grid. On the other hand, modulation ofactive power output of the wind turbine generators (WTG) aloneturns out to be inadequate due to the limited overload capabilityof the WTGs and the on- and offshore VSCs. Coordinated controlover both onshore VSC and aggregated WF output overcomes theabove limitations and is shown to be effective for power oscillationdamping. A homotopy approach is used to design the coordinatedcontroller, which can be implemented locally (at offshore WF andonshore converter site) using a decentralized architecture. Casestudies on two test systems show that the proposed controlleryields similar system dynamic response as supplementary controlthrough the WF alone.

  • Journal article
    Ge M, Kerrigan EC, 2016,

    Noise Covariance Identification for Time-varying and Nonlinear Systems

    , International Journal of Control, Vol: 90, Pages: 1903-1915, ISSN: 1366-5820

    Kalman-based state estimators assume a priori knowledge of the covariance matrices of the process and observation noise. However, in most practical situations, noise statistics and initial conditions are often unknown and need to be estimated from measurement data. This paper presents an auto-covariance least-squares-based algorithm for noise and initial state error covariance estimation of large-scale linear time-varying (LTV) and nonlinear systems. Compared to existing auto-covariance least-squares based-algorithms, our method does not involve any approximations for LTV systems, has fewer parameters to determine and is more memory/computationally efficient for large-scale systems. For nonlinear systems, our algorithm uses full information estimation/moving horizon estimation instead of the extended Kalman filter, so that the stability and accuracy of noise covariance estimation for nonlinear systems can be guaranteed or improved, respectively.

  • Journal article
    Liang L, Hou Y, Hill D, Hui SYRet al., 2016,

    Enhancing resilience of microgrids with electric springs

    , IEEE Transactions on Smart Grid, ISSN: 1949-3053

    Extreme natural events have caused severe power system blackouts in recent years. It is important for power systems to survive after such events and recover the power supply, especially for critical loads (CLs), as soon as possible. In this paper, a control strategy is proposed for electric springs (ESs) to enhance resilience of microgrids with fluctuating renewable resources. First, the feasible operating region of the ES and the power-voltage curve of the bus connected with the ES are derived analytically. Second, according to the derived feasible operating region, a novel control strategy of ES is proposed to regulate the frequency and voltage of microgrids with and without a communication system. The voltages on CLs are considered as a critical constraint for enhancing resilience during extreme natural events. Finally, the method to enhance resilience of microgrids with ES under both the frequency support mode and the voltage support mode are studied. Case studies demonstrate that ESs can enhance the resilience of microgrids with the proposed strategy with and without a communication system after extreme natural events.

  • Journal article
    Konstantelos I, Jamgotchian G, Tindemans S, Duchesne P, Cole S, Merckx C, Strbac G, Panciatici Pet al., 2016,

    Implementation of a massively parallel dynamic security assessment platform for large-scale grids

    , IEEE Transactions on Smart Grid, Vol: 8, Pages: 1417-1426, ISSN: 1949-3061

    This paper presents a computational platform for dynamic security assessment (DSA) of large electricity grids, developed as part of the iTesla project. It leverages High Performance Computing (HPC) to analyze large power systems, with many scenarios and possible contingencies, thus paving the way for pan-European operational stability analysis. The results of the DSA are summarized by decision trees of 11 stability indicators. The platform’s workflow and parallel implementation architecture is described in detail, including the way commercial tools are integrated into a plug-in architecture. A case study of the French grid is presented, with over 8000 scenarios and 1980 contingencies. Performance data of the case study (using 10,000 parallel cores) is analyzed, including task timings and data flows. Finally, the generated decision trees are compared with test data to quantify the functional performance of the DSA platform.

  • Journal article
    Battistelli C, Agalgoankar YP, Pal BC, 2016,

    Probabilistic dispatch of remote hybrid microgrids including battery storage and load management

    , IEEE Transactions on Smart Grid, Vol: 8, Pages: 1305-1317, ISSN: 1949-3061

    This work presents a probabilistic economic dispatch tool for en-ergy management (EM) studies in the context of remote hybrid AC/DC microgrids (MGs). An EM approach is proposed to en-sure a reliable power supply at the minimum cost of the hybrid MG operation. A comprehensive operational framework is pre-sented, which considers topological features of the hybrid MG and the interlinking converter between AC and DC subsections. Approach and models are tested using several operating scenari-os referred to a test hybrid MG system. In the analyses, the opportunity of integrating battery energy storage and energy demand management in the EM scheme is investigated. The results of the analyses demonstrate the effectiveness and practicality of the optimization tool in different operation contexts.

  • Journal article
    Yan S, Lee CK, Yang TB, Mok KT, Tan SC, Chaudhuri B, Ron Hui SYet al., 2016,

    Extending the Operating Range of Electric Spring using Back-To-Back Converters: Hardware Implementation and Control

    , IEEE Transactions on Power Electronics, Vol: 32, Pages: 5171-5179, ISSN: 0885-8993

    This paper presents the first hardware implementation and control of an electric spring based on a back-to-back converter configuration. Because of its ability to provide both active and reactive power compensation, this back-to-back electric spring (ES-B2B) can substantially extend the operating range of the original version of the electric spring (ES-1) and provide enhanced voltage support and suppression functions. The hardware system and control of the ES-B2B have been successfully developed and tested. The experimental results have confirmed the effectiveness of the ES-B2B in supporting and suppressing the mains voltage. Particularly, the voltage suppression ability of the ES-B2B is superior over that of ES-1. The use of ES-B2B in a simulation study of a weak power grid has also been conducted. The ES-B2B has been found to be highly effective in mitigating voltage fluctuation caused by intermittent renewable power generation.

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