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Conference paperPadoan A, Scarciotti G, Astolfi A, 2016,
A geometric characterisation of persistently exciting signals generated byautonomous systems
, 10th IFAC Symposium on Nonlinear Control Systems, Publisher: Elsevier, Pages: 826-831, ISSN: 1474-6670The persistence of excitation of signals generated by time-invariant, continuous-time,autonomous linear and nonlinear systems is studied. The notion of persistence of excitation ischaracterised as a rank condition which is reminiscent of a geometric condition used to study thecontrollability properties of a control system. The notions and tools introduced are illustratedby means of simple examples and of an application in system identification.
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Conference paperScarciotti G, Astolfi A, 2016,
Model reduction for hybrid systems with state-dependent jumps
, 10th IFAC Symposium on Nonlinear Control Systems, Publisher: Elsevier, Pages: 850-855, ISSN: 1474-6670In this paper we present a model reduction technique based on moment matchingfor a class of hybrid systems with state-dependent jumps. The problem of characterizing thesteady-state for this class of systems is studied and a result which allows to described the steadystateresponse of hybrid systems through the use of a hybrid mapping is given. Then a familyof hybrid reduced order models which achieve moment matching and are easily parameterizableis provided. The special case of periodic input signals is analyzed and conditions for applyingthe technique are given for this class. A numerical simulation illustrates the results.
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Conference paperMylvaganam T, Astolfi A, 2016,
A Nash Game Approach to Mixed H2/H∞ Control for Input-Affine Nonlinear Systems
, Nonlinear Control System Symposium (NOLCOS), Publisher: Elsevier, Pages: 1024-1029, ISSN: 1474-6670With the aim of designing controllers to simultaneously ensure robustness and optimality properties, the mixed H2/H∞ control problem is considered. A class of input-affine nonlinear systems is considered and the problem is formulated as a nonzero-sum differential game, similar to what has been done in the 1990s by Limebeer et al. for linear systems. A heuristic algorithm for obtaining solutions for the coupled algebraic Riccati equations which are characteristic of the linear quadratic problem is provided together with a systematic method for constructing approximate solutions for the general, nonlinear problem. A few numerical examples are provided.
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Conference paperXiang X, Merlin MMC, Green TC, 2016,
Cost Analysis and Comparison of HVAC, LFAC and HVDC for Offshore Wind Power Connection
, IET 12th International Conference on AC andDC Transmission, Publisher: IETLow frequency AC (LFAC) has been proposed as a means toavoid some of the large converter station costs of high voltageDC (HVDC) while delivering some of the benefits in terms ofbetter line or cable utilization and its technical feasibility hasbeen established. It is said to offer a lower costs than HVDC orconventional high voltage AC (HVAC) for a range ofintermediate distances, with HVDC becoming cheaper overlong distances. However, the basis for identifying the distancerange and extent of cost saving has not been established. Here,cost estimate methodologies are extended for LFAC. Adifficulty is the absence of commercial schemes that canprovide practical examples of costs. In this paper, costs arebroken down into constituent terms and estimates are madefrom the most similar equipment from other schemes. Thecapacity limits and power losses associated with subsea cablesare analyzed for low frequency cases. For a given powertransfer and for each distance, a choice of operating voltage,cable size and number of parallel circuits is made in order tofind the lowest route cost. This yields cost as a function ofdistance that is a non-linear and discontinuous function. Thecost curves for LFAC are compared with HVDC and HVACoptions. The results for current cost estimates show that LFAChas a range of route length over which it is the lowest costoption and but this range narrows and eventually ceases to existfor higher power transfer ratings.
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Journal articleParisini T, 2016,
Editorial
, IEEE Transactions on Control Systems Technology, Vol: 25, Pages: 1-2, ISSN: 1558-0865With this last Editorial, I’m very pleased to welcome the new Editor in Chief of the IEEE Transactions on Control Systems Technology, Prof. Andrea Serrani, effective January 1, 2017. Prof. Serrani received the Laurea (B.Eng.) degree in electrical engineering (summa cum laude) and the Ph.D. degree in artificial intelligence systems from the University of Ancona, Italy, in 1993 and 1997, respectively, and the M.S. and D.Sc. degrees in systems science and mathematics from Washinton University in St. Louis, MI, USA, in 1996 and 2000, respectively. From 1994 to 1999, he was a Fulbright Fellow at Washington University in St. Louis. Since 2002, he has been with the Department of Electrical and Computer Engineering at The Ohio State University, where he is currently a Professor and Chair of Graduate Studies. Between 2004 and 2007, he served as the technical leader for the Reusable Launch Vehicle area of the AFOSR/AFRL Collaborative Center for Control Sciences at The Ohio State University. He has held visiting positions at the Center for Research on Complex Automated Systems of the University of Bologna and at the University of Padua, Italy, and multiple summer faculty positions at the Air Force Research Laboratory, including two AF-ASEE Fellowships. Among other editorial positions, Andrea served as Associate Editor of these Transactions since 2010. Prof. Serrani has an outstanding research track record both on theory and applications. He is simply a perfect choice for this position.
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Journal articleYan S, Tan SC, Lee CK, et al., 2016,
Use of Smart Loads for Power Quality Improvement
, IEEE Journal of Emerging and Selected Topics in Power Electronics, Vol: 5, Pages: 504-512, ISSN: 2168-6777Electric spring (ES) was originally proposed as a distributed demand-side management technology for making noncritical loads adaptive to the availability of intermittent renewable power generation. The second generation of ES, fed with batteries (ES-2) and associated with a noncritical load, can form a new kind of combined smart load and distributed energy storage technology for smart grids. With its four-quadrant operation, ES-2 is able to offer ancillary grid services in addition to its major functions of voltage and frequency regulation. This paper presents the operating principles and the input current control of ES-2 for power quality improvement such as power factor correction and harmonics reduction. The operating principles and the proposed input current control have been verified with the experimental results obtained from a small-scale power grid. Another weak single-phase power system fed by intermittent wind power is set up to prove the combined operation of ES-2 for power quality improvement and ES-1 (ES with capacitor storage) for voltage stabilization. The experimental results show that ES-2 with input current control can carry out power quality improvement as its ancillary function.
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Journal articleSingh A, Pal B, 2016,
An extended linear quadratic regulator for LTI systems with exogenous inputs
, Automatica, Vol: 76, Pages: 10-16, ISSN: 0005-1098This paper proposes a cost effective control law for a linear time invariant (LTI) system having an extra set of exogenousinputs (or external disturbances) besides the traditional set of control inputs. No assumption is made with regard to a-prioriknowledge of the modeling equations for the exogenous inputs. The problem of optimal control for such a system is definedin the standard framework of linear quadratic control and an extended linear quadratic regulator (ELQR) is proposed as thesolution to the problem. The ELQR approach is demonstrated through an example and is shown to be significantly more costeffective than currently available approaches for linear quadratic control.
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Conference paperSun M, Konstantelos I, Strbac G, 2016,
Transmission network expansion planning with stochastic multivariate load and wind modeling
, PMAPS 2016, Publisher: IEEEThe increasing penetration of intermittent energy sources along with the introduction of shiftable load elements renders transmission network expansion planning (TNEP) a challenging task. In particular, the ever-expanding spectrum of possible operating points necessitates the consideration of a very large number of scenarios within a cost-benefit framework, leading to computational issues. On the other hand, failure to adequately capture the behavior of stochastic parameters can lead to inefficient expansion plans. This paper proposes a novel TNEP framework that accommodates multiple sources of operational stochasticity. Inter-spatial dependencies between loads in various locations and intermittent generation units' output are captured by using a multivariate Gaussian copula. This statistical model forms the basis of a Monte Carlo analysis framework for exploring the uncertainty state-space. Benders decomposition is applied to efficiently split the investment and operation problems. The advantages of the proposed model are demonstrated through a case study on the IEEE 118-bus system. By evaluating the confidence interval of the optimality gap, the advantages of the proposed approach over conventional techniques are clearly demonstrated.
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Conference paperVasconcelos MH, Carvalho LM, Meirinhos J, et al., 2016,
Online security assessment with load and renewable generation uncertainty: The iTesla project approach
, 2016 International Conference on Probabilistic Methods Applied to Power Systems (PMAPS), Publisher: IEEEThe secure integration of renewable generation into modern power systems requires an appropriate assessment of the security of the system in real-time. The uncertainty associated with renewable power makes it impossible to tackle this problem via a brute-force approach, i.e. it is not possible to run detailed online static or dynamic simulations for all possible security problems and realizations of load and renewable power. Intelligent approaches for online security assessment with forecast uncertainty modeling are being sought to better handle contingency events. This paper reports the platform developed within the iTesla project for online static and dynamic security assessment. This innovative and open-source computational platform is composed of several modules such as detailed static and dynamic simulation, machine learning, forecast uncertainty representation and optimization tools to not only filter contingencies but also to provide the best control actions to avoid possible unsecure situations. Based on High Performance Computing (HPC), the iTesla platform was tested in the French network for a specific security problem: overload of transmission circuits. The results obtained show that forecast uncertainty representation is of the utmost importance, since from apparently secure forecast network states, it is possible to obtain unsecure situations that need to be tackled in advance by the system operator.
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Journal articleScarciotti 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: 0885-8993Power 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.
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Journal articleRiverso S, Boem F, Ferrari-Trecate G, et al., 2016,
Plug-and-Play Fault Detection and control-reconfiguration for a class of nonlinear large-scale constrained systems
, IEEE Transactions on Automatic Control, Vol: 61, Pages: 3963-3978, ISSN: 0018-9286This paper deals with a novel Plug-and-Play (PnP) architecture for the control and monitoring of Large-Scale Systems (LSSs). The proposed approach integrates a distributed Model Predictive Control (MPC) strategy with a distributed Fault Detection (FD) architecture and methodology in a PnP framework. The basic concept is to use the FD scheme as an autonomous decision support system: once a fault is detected, the faulty subsystem can be unplugged to avoid the propagation of the fault in the interconnected LSS. Analogously, once the issue has been solved, the disconnected subsystem can be re-plugged-in. PnP design of local controllers and detectors allow these operations to be performed safely, i.e. without spoiling stability and constraint satisfaction for the whole LSS. The PnP distributed MPC is derived for a class of nonlinear LSSs and an integrated PnP distributed FD architecture is proposed. Simulation results in two paradigmatic examples show the effectiveness and the potential of the general methodology.
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Journal articleArana C, Evangelou SA, Dini D, 2016,
Series active variable geometry suspension application to comfort enhancement
, Control Engineering Practice, Vol: 59, Pages: 111-126, ISSN: 1873-6939This paper explores the potential of the Series Active Variable Geometry Suspension (SAVGS) for comfort and road holding enhancement. The SAVGS concept introduces significant nonlinearities associated with the rotation of the mechanical link that connects the chassis to the spring-damper unit. Although conventional linearization procedures implemented in multi-body software packages can deal with this configuration, they produce linear models of reduced applicability. To overcome this limitation, an alternative linearization approach based on energy conservation principles is proposed and successfully applied to one corner of the car, thus enabling the use of linear robust control techniques. An H∞ controller is synthesized for this simplified quarter-car linear model and tuned based on the singular value decomposition of the system's transfer matrix. The proposed control is thoroughly tested with one-corner and full-vehicle nonlinear multi-body models. In the SAVGS setup, the actuator appears in series with the passive spring-damper and therefore it would typically be categorized as a low bandwidth or slow active suspension. However, results presented in this paper for an SAVGS-retrofitted Grand Tourer show that this technology has the potential to also improve the high frequency suspension functions such as comfort and road holding.
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Conference paperChaffey 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: IETProtecting 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.
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Journal articleChang 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: 1751-8857The 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.
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Conference paperNduka OS, Pal BC, 2016,
Harmonic characterisation model of grid interactive photovoltaic systems
, 2016 IEEE International Conference on Power System Technology (POWERCON), Publisher: IEEEThis 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.
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Journal articleKonstantelos I, Pudjianto D, Strbac G, et al., 2016,
Integrated North Sea grids: The costs, the benefits and their distribution between countries
, Energy Policy, Vol: 101, Pages: 28-41, ISSN: 0301-4215A 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.
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Journal articleVinter 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: 0363-0129This 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.
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Journal articleForni 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: 1872-7956In 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.
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Conference paperBeddard A, Wang W, Barnes M, et 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: 1944-9925Accurate 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.
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Conference paperChakravorty D, Akhtar Z, Chaudhuri B, et al., 2016,
Comparison of Primary Frequency Control Using Two Smart Load Types
, IEEE Power and Energy Society General Meeting, Publisher: IEEE, ISSN: 1944-9933Primary 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.
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Conference paperMartınez-Sanz IM, Chaudhuri B, Junyent-Ferre A, et al., 2016,
Distributed vs. Concentrated Rapid Frequency Response Provision in Future Great Britain System
, IEEE Power and Energy Society General Meeting, Publisher: IEEE, ISSN: 1944-9933Two 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.
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Conference paperGe M, Kerrigan EC, 2016,
Short-term ocean wave forecasting using an autoregressive moving average model
, Control 2016 - 11th International Conference on Control, Publisher: IEEEIn 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.
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Conference paperBoem 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: IEEEThe 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.
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Journal articleAhmad 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: 1751-8644The 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.
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Journal articleCalvo 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: 2352-4677Thepower 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.
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Conference paperWaffenschmidt E, Hui RSY, 2016,
Virtual inertia with PV inverters using DC-link capacitors
, EPE 20161 ECCE Europe, Publisher: IEEESoon, 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.
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Conference paperJudge PD, Merlin MMC, Green TC, et 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 CurrentAchieving 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.
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Journal articleTeng 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: 2196-5625Energy 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.
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Journal articleKuenzel 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: 1558-0679This 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.
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Conference paperChaffey GP, judge PD, Green TC, 2016,
Energy Requirements for Modular Circuit Breakers in Multiterminal HVDC Networks
, HVDC 2016, International Conference on. CSEE, 2016.
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