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  • Journal article
    Zhong W, Hui SYR, 2015,

    Auxiliary Circuits for Power Flow Control in Multifrequency Wireless Power Transfer Systems With Multiple Receivers

    , IEEE TRANSACTIONS ON POWER ELECTRONICS, Vol: 30, Pages: 5902-5910, ISSN: 0885-8993
  • Journal article
    Ng WM, Hui SYR, 2015,

    Ultralow-Loss Passive T5 Fluorescent Lamp Ballasts for Subzero Temperature Operation

    , IEEE TRANSACTIONS ON POWER ELECTRONICS, Vol: 30, Pages: 5792-5799, ISSN: 0885-8993
  • Conference paper
    Scarciotti G, 2015,

    Model reduction of power systems with preservation of slow and poorly damped modes

    , IEEE PES General Meeting 2015, Publisher: IEEE, Pages: 1-5, ISSN: 1944-9925

    In this paper a recently proposed variation of the Krylov subspace method for model reduction is applied to power systems. The technique allows to easily enforce constraints on the reduced order model. Herein this is used to preserve the slow and poorly damped modes of the systems in the reduced order model. We analyze the role that these modes have in obtaining a good approximation and we show that the order of the reduced model can be decreased if the 'right' modes are preserved. We validate the theory on the 68-Bus, 16-Machine, 5-Area benchmark system (NETS-NYPS).
  • Journal article
    Newbery D, Strbac G, 2015,

    What is needed for battery electric vehicles to become socially cost competitive?

    , Economics of Transportation, Vol: 5, Pages: 1-11, ISSN: 2212-0122

    Battery electric vehicles (BEVs) could be key to decarbonizing transport, but are heavily subsidized. Most assessments of BEVs use highly taxed road fuel prices and ignore efficient pricing of electricity. We use efficient prices for transport fuels and electricity, to judge what battery costs would make BEVs cost competitive. High mileage, low discount rates and high oil prices could make BEVs cost competitive by 2020, and by 2030 fuel costs are comparable over a wider range. Its contribution lies in careful derivation of efficient fuel and electricity prices and the concept of a target battery cost.
  • Journal article
    Scarciotti G, Astolfi A, 2015,

    Model reduction by matching the steady-state response of explicit signal generators

    , IEEE Transactions on Automatic Control, Vol: 99, ISSN: 1558-2523
  • Conference paper
    Calvo JL, Tindemans S, Strbac G, 2015,

    Managing Risks from Reverse Flows under Distribution Network Outage Scenarios

    , IET International Conference on Resilience of Transmission and Distribution Networks (RTDN 2015), Publisher: IET

    Distribution networks have been traditionally conceived fortransporting electricity downstream into low voltage demandnodes. However, the connection of significant amounts ofdistributed generation may reverse this condition, resulting indistribution nodes exporting power to other parts of thenetwork. The current planning standard of the UK distributionnetworks (Engineering recommendation P2/6) requires makingavailable sufficient capacity and redundancy for downstreamflows under peak demand levels. However, it does notexplicitly consider the implications of DG-mediated flowreversals that may cause flow constraints under circuit outageconditions. Relying on a Monte Carlo approach to sample windand demand with adjustable correlations, this paper providesinsights into the risks associated with an increase of variabledistributed generation to the point where reverse flows mayexceed the connection capacity under circuit outage conditions.Remote tripping schemes that disconnect distributedgenerators upon occurrence of a fault are explored to mitigateoutage related costs. The latter strategy carries benefits but alsonovel risks in the form of a reliance on real-timecommunication and control, which may malfunction. It isshown that even unreliable corrective actions conveysignificant benefits to system reliability.
  • Conference paper
    Djapic P, Tindemans S, Strbac G, 2015,

    Comparison of Approaches for Quantifying Demand Side Response Capacity Credit for the Use in Distribution Network Planning

    , IET International Conference on Resilience of Transmission and Distribution Networks (RTDN 2015), Publisher: IET

    The present UK distribution network planning standard,Engineering Recommendation P.2/6 (P2/6), defines theacceptable durations of supply outages following first andsecond circuit outage conditions as function of group demand.In addition, P2/6 specifies a capacity value for distributedgeneration (DG) to be used in future circuit capacity planning.The approach does not consider other elements of thedistribution network. This paper analyses the reliabilityperformance of distribution system when DSR is used todefer network upgrades driven by load growth. The analysisuses actual DSR performance data from trials that wereexecuted as part of the Low Carbon London project. The DSRcontribution to security of supply is assessed using aprobabilistic risk modelling framework to further inform anumber of topics (i) reliability contribution of DSRtechnologies in a network context, (ii) strengths andweaknesses of P2/6 in estimating contribution to security ofsupply, (iii) benefits of contractual redundancy, (iv) impact ofDSR coincidence in delivery (common mode failures) oncontribution to security, and (v) impact of DSR scale andmagnitude on contribution to security of supply.
  • Journal article
    Colet-Subirachs A, Gomis-Bellmunt O, Clos-Costa D, Martin-Segura G, Junyent-Ferre A, Villafafila-Robles R, Ferrer-Marti Let al., 2010,

    Electromechanical Modelling and Control of a Micro-Wind Generation System for Isolated Low Power DC Micro Grids

    , EPE JOURNAL, Vol: 20, Pages: 42-48, ISSN: 0939-8368
  • Journal article
    Li S, Qi W, Tan SC, Hui SYRet al., 2015,

    Integration of an Active Filter and a Single-Phase AC/DC Converter with Reduced Capacitance Requirement and Component Count

    , IEEE Transactions on Power Electronics, Vol: 31, Pages: 4121-4137, ISSN: 0885-8993

    Existing methods of incorporating an active filter into an AC/DC converter for eliminating electrolytic capacitors usually require extra power switches. This inevitably leads to an increased system cost and degraded energy efficiency. In this paper, a concept of active-filter integration for single-phase AC/DC converters is reported. The resultant converters can provide simultaneous functions of power factor correction, DC voltage regulation, and active power decoupling for mitigating the low-frequency DC voltage ripple, without an electrolytic capacitor and extra power switch. To complement the operation, two closed-loop voltage-ripple-based reference generation methods are developed for controlling the energy storage components to achieve active power decoupling. Both simulation and experiment have confirmed the eligibility of the proposed concept and control methods in a 210-W rectification system comprising an H-bridge converter with a half-bridge active filter. Interestingly, the end converters (Type I and Type II) can be readily available using a conventional H-bridge converter with minor hardware modification. A stable DC output with merely 1.1% ripple is realized with two 50-μF film capacitors. For the same ripple performance, a 900-μF capacitor is required in conventional converters without an active filter. Moreover, it is found out that the active-filter integration concept might even improve the efficiency performance of the end converters as compared with the original AC/DC converter without integration.
  • Journal article
    Padoan A, Astolfi A, 2015,

    A Note on Delay Coordinates for Locally Observable Analytic Systems

    , IEEE Transactions on Automatic Control, Vol: 61, Pages: 1409-1412, ISSN: 1558-2523

    In this short note, the problem of locally reconstructing the state of a nonlinear system is studied. To avoid computational difficulties arising in the numerical differentiation of the output, the so-called delay coordinates are considered. The assumptions of analyticity and (local) observability of the system are shown to imply that a family of mappings, induced by the delay coordinates and parameterized by a time delay parameter, gives a local diffeomorphism for generic values of such delay parameter on a certain set. A worked-out example illustrates the result.
  • Conference paper
    Das HB, Evangelou SA, Dhinagar SJ, 2015,

    An objective analysis of drivability for two wheeler powertrain with control oriented dynamic model

    , Pages: 292-299, ISSN: 1474-6670

    The objective of this work is to estimate drivability characteristics parameters of two wheeler powertrain with control oriented powertrain model. The evaluation is essential for defining drivability characteristics for a future electric variable transmission (EVT) powertrain. The mathematical model for the complete powertrain is developed using suitable modeling approaches for the different sub-modules of the complete system. The Spark Ignition (SI) engine model used for this work is developed from mean value model approach and experimentally validated with test data from TVS Motor Company, India. The model is integrated with two types of transmission models, Continuous Variable Transmission (CVT) and Manual Transmission (MT). It simulates dynamic power-flow from the engine to wheel for analyzing longitudinal drivability of the vehicle for both powertrain configurations. It is proposed that the drivability can be measured with certain parameters which show good correlation with subjective assessments for vehicle launch as well as tip in condition. The objective assessment of both types of powertrains is performed using the above mentioned powertrain models. The results of the simulation for drivability tests are discussed in this paper.
  • Journal article
    Nunna K, Sassano M, Astolfi A, 2015,

    Constructive interconnection and damping assignment for port-controlled Hamiltonian systems

    , IEEE Transactions on Automatic Control, Vol: 60, Pages: 2350-2361, ISSN: 0018-9286

    The Interconnection and Damping Assignment Passivity-Based Control (IDA-PBC) problem for port-controlled Hamiltonian systems is revisited. We propose a methodology that exploits the novel notion of algebraic solution of the so-called matching equation. This notion is instrumental for the construction of an energy function, defined on an extended state-space, which does not rely upon the solution of any partial differential equation. This yields, differently from the classical solution, a dynamic state feedback that stabilizes a desired equilibrium point. In addition, conditions that allow to preserve the port-controlled Hamiltonian structure in the extended closed-loop system are provided. The theory is validated on two physical systems: the magnetic levitated ball and a third order food-chain system. A dynamic control law is constructed for both these systems by assigning a damping factor that cannot be assigned by the classical IDA-PBC.
  • Journal article
    Prieto-Araujo E, Junyent-Ferre A, Lavernia-Ferrer D, Gomis-Bellmunt Oet al., 2015,

    Decentralized Control of a Nine-Phase Permanent Magnet Generator for Offshore Wind Turbines

    , IEEE Transactions on Energy Conversion, Vol: 30, Pages: 1103-1112, ISSN: 0885-8969

    This paper presents a decentralized current controlapproach for a nine-phase wind turbine generator. This type ofgenerator has three different three-phase stators sharing the samemachine yoke and connected to the grid by means of three differentvoltage source back-to-back power converters. Due to themachine configuration, magnetic couplings are present betweenthe three stators, complicating the design and implementation ofthe machine current controllers. Rather than a centralized controlapproach, this paper proposes a methodology to design a decentralizedmachine control to regulate the active and reactive powerflowing through each stator independently. A complete dynamicanalysis is performed in order to design the controller to reducethe coupling effects within the machine, while ensuring a properdynamic performance. The control strategy is validated throughsimulation and experimental results.
  • Journal article
    Tindemans SH, Trovato V, Strbac G, 2015,

    Decentralized control of thermostatic loads for flexible demand response

    , IEEE Transactions on Control Systems Technology, Vol: 23, Pages: 1685-1700, ISSN: 1063-6536

    Thermostatically controlled loads (TCLs), such as refrigerators, air-conditioners and space heaters, offer significant potential for short-term modulation of their aggregate power consumption. This ability can be used in principle to provide frequency response services, but controlling a multitude of devices to provide a measured collective response has proven to be challenging. Many controller implementations struggle to manage simultaneously the short-term response and the long-term payback, whereas others rely on a real-time command-and-control infrastructure to resolve this issue. In this paper, we propose a novel approach to the control of TCLs that allows for accurate modulation of the aggregate power consumption of a large collection of appliances through stochastic control. By construction, the control scheme is well suited for decentralized implementation, and allows each appliance to enforce strict temperature limits. We also present a particular implementation that results in analytically tractable solutions both for the global response and for the device-level control actions. Computer simulations demonstrate the ability of the controller to modulate the power consumption of a population of heterogeneous appliances according to a reference power profile. Finally, envelope constraints are established for the collective demand response flexibility of a heterogeneous set of TCLs.
  • Journal article
    Yang Y, Mok K-T, Tan S-C, Hui SYRet al., 2015,

    Nonlinear Dynamic Power Tracking of Low-Power Wind Energy Conversion System

    , IEEE TRANSACTIONS ON POWER ELECTRONICS, Vol: 30, Pages: 5223-5236, ISSN: 0885-8993
  • Journal article
    Teng F, Aunedi M, Pudjianto D, Strbac Get al., 2015,

    Benefits of demand-side response in providing frequency response service in the future GB power system

    , Frontiers in Energy Research, Vol: 3, ISSN: 2296-598X

    The demand for ancillary service is expected to increase significantly in the future Great Britain (GB) electricity system due to high penetration of wind. In particular, the need for frequency response, required to deal with sudden frequency drops following a loss of generator, will increase because of the limited inertia capability of wind plants. This paper quantifies the requirements for primary frequency response and analyses the benefits of frequency response provision from demand-side response (DSR). The results show dramatic changes in frequency response requirements driven by high penetration of wind. Case studies carried out by using an advanced stochastic generation scheduling model suggest that the provision of frequency response from DSR could greatly reduce the system operation cost, wind curtailment, and carbon emissions in the future GB system characterized by high penetration of wind. Furthermore, the results demonstrate that the benefit of DSR shows significant diurnal and seasonal variation, whereas an even more rapid (instant) delivery of frequency response from DSR could provide significant additional value. Our studies also indicate that the competing technologies to DSR, namely battery storage, and more flexible generation could potentially reduce its value by up to 35%, still leaving significant room to deploy DSR as frequency response provider.
  • Report
    Canizares C, Fernandes T, Geraldi Jr E, Gerin-Lajoie L, Gibbard M, Hiskens I, Kersulis J, Kuiava R, Lima L, Marco FD, Martins N, Pal BC, Piardi A, Ramos R, Santos JD, Silva D, Singh AK, Tamimi B, Vowels Det al., 2015,

    Benchmark Systems for Small-Signal Stability Analysis and Control

    , Publisher: IEEE Power and Energy Society

    This report documents the work of the IEEE PES Task Force (TF) on Benchmark Systems for Stability Controls. The following sections present the objectives of the TF, the guidelines used to select the benchmarks, a brief description of each benchmark system so the reader can select the most suitable system for the intended application, the input data and results for each benchmark system, and a set of conclusions.Detailed descriptions of each system are also presented in the Appendices to this report and in the website created by this Task Force to share the data and simulation results related to the benchmark systems.
  • Journal article
    Singh AK, Pal BC, 2015,

    Decentralized Control of Oscillatory Dynamics in Power Systems using an Extended LQR

    , IEEE Transactions on Power Systems, Vol: 31, Pages: 1715-1728, ISSN: 1558-0679

    This paper proposes a decentralized algorithm for real-time control of oscillatory dynamics in power systems. The algorithm integrates dynamic state estimation (DSE) with an extended linear quadratic regulator (ELQR) for optimal control. The control for one generation unit only requires measurements and parameters for that unit, and hence the control at a unit remains completely independent of other units. The control gains are updated in real-time, therefore the control scheme remains valid for any operating condition. The applicability of the proposed algorithm has been demonstrated on a representative power system model.
  • Journal article
    de Souza JCS, Lessa Assis TM, Pal BC, 2015,

    Data compression in smart distribution systems via singular value decomposition

    , IEEE Transactions on Smart Grid, Vol: 8, Pages: 275-284, ISSN: 1949-3061

    Electrical distribution systems have been experiencingmany changes in recent times. Advances in metering systeminfrastructure and the deployment of a large number of smartmeters in the grid will produce a big volume of data thatwill be required for many different applications. Despite thesignificant investments taking place in the communications infrastructure,this remains a bottleneck for the implementation ofsome applications. This paper presents a methodology for lossydata compression in smart distribution systems using the singularvalue decomposition technique. The proposed method is capableof significantly reducing the volume of data to be transmittedthrough the communications network and accurately reconstructingthe original data. These features are illustrated by resultsfrom tests carried out using real data collected from meteringdevices at many different substations.
  • Journal article
    Zhang X, Green TC, 2015,

    The modular multilevel converter for high step-up ratio DC-DC conversion

    , IEEE Transactions on Industrial Electronics, Vol: 62, Pages: 4925-4936, ISSN: 0278-0046

    High step-up ratio dc-dc converters with megawatt ratings are of interest in wind turbine interfaces and high-voltage direct-current systems. This paper presents a modular multilevel dc-dc converter based on the standard boost converter topology but with the normal single switches replaced by a number of capacitor-clamped submodules. The converter is operated in resonant mode with resonance between submodule capacitors and the arm inductor. A phase-shifted switching arrangement is applied such that there is a constant number, i.e., N, of submodules supporting the high voltage at a time. In this operation mode, the step-up ratio is dependent on the number of submodules and the inductor charging ratio. The converter exhibits scalability without using a transformer and is capable of bidirectional power flow. An application example of a wind turbine interface with a 10 : 1 conversion ratio is demonstrated in simulation. The experimental verification of the concept using a lab-scale prototype is provided.
  • Journal article
    Li S, Zhu G-R, Tan S-C, Hui SYRet al., 2015,

    Direct AC/DC Rectifier With Mitigated Low-Frequency Ripple Through Inductor-Current Waveform Control

    , IEEE TRANSACTIONS ON POWER ELECTRONICS, Vol: 30, Pages: 4336-4348, ISSN: 0885-8993
  • Conference paper
    Judge PD, Chaffey G, Clemow P, Merlin MMC, Green TCet al., 2015,

    Hardware testing of the alternate arm converter operating in its extended overlap mode

    , International High Voltage Direct Current 2015 Conference (HVDC2015)
  • Conference paper
    Jiang J, Astolfi A, 2015,

    Shared-control for the kinematic model of a rear-wheel drive car

    , American Control Conference, Publisher: IEEE, Pages: 1155-1160, ISSN: 0743-1619

    This paper presents a shared-control algorithm for the kinematic model of a rear-wheel drive car, for which the set of feasible Cartesian positions is defined by a group of linear inequalities. The shared-control scheme is based on a hysteresis switch and its properties are established by a Lyapunov-like analysis. Simple numerical examples demonstrate the effectiveness of the shared-control law.
  • Journal article
    Scarciotti G, Astolfi A, 2015,

    Model reduction of neutral linear and nonlinear time-invariant time-delay systems with discrete and distributed delays

    , IEEE Transactions on Automatic Control, Vol: 99, ISSN: 1558-2523

    The problem of model reduction by moment matching for linear and nonlinear differential time-delay systems is studied. The class of models considered includes neutral differential time-delay systems with discrete-delays and distributeddelays. The description of moment is revisited by means of a Sylvester-like equation for linear time-delay systems and by means of the center manifold theory for nonlinear time-delay systems. In addition the moments at infinity are characterized for both linear and nonlinear time-delay systems. Parameterized families of models achieving moment matching are given. The parameters can be exploited to derive delay-free reduced order models or time-delay reduced order models with additional properties, e.g. interpolation at an arbitrary large number of points. Finally, the problem of obtaining a reduced order model of an unstable system is discussed and solved.
  • Journal article
    Aldhaher S, yates D, Mitcheson P, 2015,

    Modelling and Analysis of Class EF and Class E/F Inverters with series-tuned resonant networks

    , IEEE Transactions on Power Electronics, Vol: 31, Pages: 3415-3430, ISSN: 0885-8993

    Class EF and Class E/F inverters are hybrid inverters that combine the improved switch voltage and current waveforms of Class F and Class F-1 inverters with the efficient switching of Class E inverters. As a result, their efficiency, output power and power output capability can be higher in some cases than the Class E inverter. Little is known about these inverters and no attempt has been made to provide an in depth analysis on their performance. The design equations that have been previously derived are limited and are only applicable under certain assumptions. This paper is the first to provide a comprehensive set of analytical analysis of Class EF and Class E/F inverters. The Class EF2 inverter is then studied in further detail and three special operation cases are defined that allow it to either operate at maximum power-output capability, maximum switching frequency or maximum output power. Final design equations are provided to allow for rapid design and development. Experimental results are provided to confirm the accuracy of the performed analysis based on a 23W Class EF2 inverter at 6.78MHz and 8.60MHz switching frequencies. The results also show that the Class EF2 inverter achieved an efficiency of 91% compared to a 88% efficiency when operated as a Class E inverter.
  • Conference paper
    Tindemans SH, Strbac G, 2015,

    Visualising risk in generating capacity adequacy studies using clustering and prototypes

    , IEEE Power and Energy Society General Meeting, 2015, Publisher: IEEE

    Generating capacity adequacy studies play a significantrole in long term capacity planning. Risks of capacitydeficits are usually reported in the form of one or more averagequantities, which cannot fully convey the nature of the risksbeing faced. Chronological Monte Carlo simulations may be usedto construct comprehensive multi-dimensional risk profiles, butsuch profiles tend to be difficult to interpret. This paper proposesthe use of a clustering method to partition the risk profile intoclusters of similar outcomes with associated probabilities. Theresults are presented in accessible tabular form, and prototypicalscenarios can be analysed in detail to provide further insight.
  • Conference paper
    Mylvaganam T, Astolfi A, 2015,

    Control of Microgrids Using a Differential Game Theoretic Framework

    , Conference on Decision and Control
  • Journal article
    Palladino M, Vinter RB, 2015,

    Regularity of the Hamiltonian Along Optimal Trajectories

    , SIAM Journal on Control and Optimization, Vol: 53, Pages: 1892-1919, ISSN: 1095-7138

    This paper concerns state constrained optimal control problems, in which the dynamic constraint takes the form of a differential inclusion. If the differential inclusion does not depend on time, then the Hamiltonian, evaluated along the optimal state trajectory and the co-state trajectory, is independent of time. If the differential inclusion is Lipschitz continuous, then the Hamiltonian, evaluated along the optimal state trajectory and the co-state trajectory, is Lipschitz continuous. These two well-known results are examples of the following principle: the Hamiltonian, evaluated along the optimal state trajectory and the co-state trajectory, inherits the regularity properties of the differential inclusion, regarding its time dependence. We show that this principle also applies to another kind of regularity: if the differential inclusion has bounded variation w.r.t. time, then the Hamiltonian, evaluated along the optimal state trajectory and the co-state trajectory, has bounded variation. Two applications of these newly found properties are demonstrated. One is to derive improved conditions which guarantee the nondegeneracy of necessary conditions of optimality in the form of a Hamiltonian inclusion. The other application is to derive new conditions under which minimizers in the calculus of variations have bounded slope. The analysis is based on a recently proposed, local concept of differential inclusions that have bounded variation w.r.t. the time variable, in which conditions are imposed on the multifunction involved, only in a neighborhood of a given state trajectory.
  • Conference paper
    Boem F, Xu Y, Fischione C, Parisini Tet al., 2015,

    A distributed pareto-optimal dynamic estimation method

    , 2015 European Control Conference (ECC 2015), Publisher: IEEE, Pages: 3673-3680

    In this paper, a novel distributed model-based prediction method is proposed using sensor networks. Each sensor communicates with the neighboring nodes for state estimation based on a consensus protocol without centralized coordination. The proposed distributed estimator consists of a consensus-filtering scheme, which uses a weighted combination of sensors information, and a model-based predictor. Both the consensus-filtering weights and the model-based prediction parameter for all the state components are jointly optimized to minimize the variance and bias of the prediction error in a Pareto framework. It is assumed that the weights of the consensus-filtering phase are unequal for the different state components, unlike consensus-based approaches from literature. The state, the measurements, and the noise components are assumed to be individually correlated, but no probability distribution knowledge is assumed for the noise variables. The optimal weights are derived and it is established that the consensus-filtering weights and the model-based prediction parameters cannot be designed separately in an optimal way. The asymptotic convergence of the mean of the prediction error is demonstrated. Simulation results show the performance of the proposed method, obtaining better results than distributed Kalman filtering.
  • Conference paper
    Giannelos S, Konstantelos I, Strbac G, 2015,

    Option value of Soft Open Points in distribution networks

    , IEEE Powertech, Publisher: IEEE

    We propose a novel stochastic planning model thatconsiders investment in conventional assets as well as in SoftOpen Points, as a means of treating voltage and thermalconstraints caused by the increased penetration of renewabledistributed generation (DG) sources. Soft Open Points areshown to hold significant option value under uncertainty;however, their multiple value streams remain undetected undertraditional deterministic planning approaches, potentiallyundervaluing this technology and leading to a higher risk ofstranded assets.

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