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  • CONFERENCE PAPER
    Carmichael R, Schofield J, Bilton M, Ozaki R, Strbac Get al.,

    Dynamic pricing of electricity for wind-following?: Understanding demand-response and consumer engagement on the UK’s first trial of a dynamic time-of-use tariff for residential electricity

    , BEHAVE 2014 Conference
  • CONFERENCE PAPER
    Kuenzel S, Kunjumuhammed LP, Pal BC, Erlich Iet al.,

    Wind Power Plants Inertial Response Capability Considering Wake Effect

    , 11th International Workshop on Large-Scale Integration of Wind Power into Power Systems as well as on Transmission Networks for Offshore Wind Power Plants, Lisbon
  • JOURNAL ARTICLE
    Vinter RB, Bettiol P,

    Trajectories satisfying a state constraint: improved estimates and new non-degeneracy conditions

    , IEEE Transactions on Automatic Control, Vol: 56, Pages: 1090-1096

    For a state-constrained control system described by a differential inclusion and a single functional inequality state constraint, it is known that, under an `inward pointing condition', the $W^{1,1}$ distance of an arbitrary state trajectory to the set of state trajectories, which have the same left endpoint and which satisfy the state constraint, is linearly related to the state constraint violation. In this paper we show that, in situations where the state-constrained control system is described instead by a controlled differential equation, this estimate can be improved by replacing the $W^{1,1}$ distance on state trajectories by the Ekeland metric of the distance of the control functions. A counter-example reveals that a refinement of this nature is not in general valid for state constrained differential inclusions. Finally we show how the refined estimates may be used to establish new conditions for non-degeneracy of the state constrained Maximum Principle, in circumstances when the data depends discontinuously on the control variable.

  • JOURNAL ARTICLE
    Nanchian S, Majumdar A, Pal BC, Nanchian S, Majumdar A, Pal BC, Nanchian S, Majumdar A, Pal BC, Nanchian S, Majumdar A, Pal BCet al., 2017,

    Three-Phase State Estimation Using Hybrid Particle Swarm Optimization

    , IEEE TRANSACTIONS ON SMART GRID, Vol: 8, Pages: 1035-1045, ISSN: 1949-3053

    © 2015 IEEE. This paper proposes a method for three-phase state estimation (SE) in power distribution network including on-load 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.

  • JOURNAL ARTICLE
    Pipelzadeh Y, Chaudhuri NR, Chaudhuri B, Green TC, Pipelzadeh Y, Chaudhuri NR, Chaudhuri B, Green TC, Pipelzadeh Y, Chaudhuri NR, Chaudhuri B, Green TC, Pipelzadeh Y, Ray Chaudhuri N, Chaudhuri B, Green TC, Pipelzadeh Y, Chaudhuri B, Green TCet al., 2017,

    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: 0885-8950

    © 2017 IEEE. Damping contribution from wind farms (WFs) is likely to become a mandatory requirement as a part of the grid codes. For remote offshore WFs, connected through a voltage source converter (VSC)-based direct current link, the most convenient option for the onshore transmission system operator (TSO) is to modulate the reactive power at the onshore VSC within their own jurisdiction. In this paper, we show that supplementary control through the onshore VSC alone, although attractive for TSOs, could result in undesirable voltage variations in the onshore grid. On the other hand, modulation of active power output of the wind turbine generators (WTG) alone turns out to be inadequate due to the limited overload capability of the WTGs. Coordinated control over both onshore VSC and aggregated WF output overcomes the above limitations and is shown to be effective for power oscillation damping. A homotopy approach is used to design the coordinated controller, which can be implemented locally (at offshore WF and onshore converter site) using a decentralized architecture. This is a bilinear matrix inequality problem, which is solved by transforming these constraints into linear matrix inequality constraints. Case studies on two test systems show that the proposed controller yields similar system dynamic response as supplementary control through the WF alone.

  • JOURNAL ARTICLE
    Stacchini de Souza JC, Lessa Assis TM, Pal BC, de Souza JCS, Assis TML, Pal BC, de Souza JCS, Lessa Assis TM, Pal BC, de Souza JCS, Lessa Assis TM, Pal BCet al., 2017,

    Data Compression in Smart Distribution Systems via Singular Value Decomposition

    , IEEE TRANSACTIONS ON SMART GRID, Vol: 8, Pages: 275-284, ISSN: 1949-3053

    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
    Tindemans SH, Strbac G, Tindemans S, Strbac G, Tindemans SH, Strbac G, Tindemans SH, Strbac G, Tindemans SH, Strbac Get al., 2017,

    Robust estimation of risks from small samples

    , Philosophical Transactions A: Mathematical, Physical and Engineering Sciences, Vol: 375, Pages: 20160299-20160299, ISSN: 1471-2962

    Data-driven risk analysis involves the inference of probability distributions from measured or simulated data. In the case of a highly reliable system, such as the electricity grid, the amount of relevant data is often exceedingly limited, but the impact of estimation errors may be very large. This paper presents a robust nonparametric Bayesian method to infer possible underlying distributions. The method obtains rigorous error bounds even for small samples taken from ill-behaved distributions. The approach taken has a natural interpretation in terms of the intervals between ordered observations, where allocation of probability mass across intervals is well-specified, but the location of that mass within each interval is unconstrained. This formulation gives rise to a straightforward computational resampling method: Bayesian Interval Sampling. In a comparison with common alternative approaches, it is shown to satisfy strict error bounds even for ill-behaved distributions.

  • JOURNAL ARTICLE
    Arana C, Evangelou SA, Dini D, Arana C, Evangelou SA, Dini D, Arana C, Evangelou S, Dini D, Arana C, Evangelou SA, Dini Det al., 2016,

    Series Active Variable Geometry Suspension Application to Chassis Attitude Control

    , IEEE-ASME TRANSACTIONS ON MECHATRONICS, Vol: 21, Pages: 518-530, ISSN: 1083-4435

    © 1996-2012 IEEE. This paper explores the application of the recently introduced series active variable geometry suspension (SAVGS) to the control of chassis attitude motions and the directional response of cars. A codesign methodology, involving a component dimensioning framework and a multiobjective control scheme, is developed to maximize the SAVGS control capabilities, while respecting vehicle and actuator design constraints. The dimensioning framework comprises: a steady-state mathematical model based on the principle of virtual work; a parameter sensitivity analysis that sheds light on the dependencies that exist between the properties of the passive suspension, the SAVGS, and the chassis; and an algorithm to size the main SAVGS components for any given vehicle and steady-state performance objectives. The general multiobjective control scheme is presented for general application, and the particular case of combined chassis attitude control and overturning couple distribution control is developed in detail. The proposed scheme is subsequently applied to a high-performance sports car and a fully laden SUV, and tested under a wide range of operating conditions through the simulation of standard open-loop maneuvers. Results demonstrate the SAVGS potential to favorably regulate the attitude motions and directional response in both vehicle classes.

  • JOURNAL ARTICLE
    Bachtiar V, Kerrigan EC, Moase WH, Manzie C, Bachtiar V, Kerrigan EC, Moase WH, Manzie Cet al., 2016,

    Continuity and monotonicity of the MPC value function with respect to sampling time and prediction horizon

    , Automatica, Vol: 63, Pages: 330-337, ISSN: 0005-1098

    The digital implementation of model predictive control (MPC) is fundamentally governed by two design parameters; samplingtime and prediction horizon. Knowledge of the properties of the value function with respect to the parameters can be used fordeveloping optimisation tools to find optimal system designs. In particular, these properties are continuity and monotonicity.This paper presents analytical results to reveal the smoothness properties of the MPC value function in open- and closed-loopfor constrained linear systems. Continuity of the value function and its differentiability for a given number of prediction stepsare proven mathematically and confirmed with numerical results. Non-monotonicity is shown from the ensuing numericalinvestigation. It is shown that increasing sampling rate and/or prediction horizon does not always lead to an improved closedloopperformance, particularly at faster sampling rates.

  • JOURNAL ARTICLE
    Kunjumuhammed LP, Pal BC, Oates C, Dyke KJ, Kunjumuhammed LP, Pal BC, Oates C, Dyke KJ, Kunjumuhammed LP, Pal BC, Oates C, Dyke Ket al., 2016,

    Electrical Oscillations in Wind Farm Systems: Analysis and Insight Based on Detailed Modeling

    , IEEE TRANSACTIONS ON SUSTAINABLE ENERGY, Vol: 7, Pages: 51-62, ISSN: 1949-3029

    The paper presents modelling and analysis of electricaloscillations in a wind farm system. The detailed modellingand modal analysis of a wind farm system is presented in thispart of a two-part paper. The approach to modelling uses detailedrepresentation of a wind turbine generator and collection systemincluding HVDC power converter system control, facilitating acomprehensive analysis of wind farm system. Various modes areclassified according to the frequency of oscillation. The detailedmodal analysis is used to characterize the critical modes. Timedomain simulation also confirms the presence of these modes.The effect of wind farm operating conditions and voltage sourceconverter control tuning on critical oscillatory modes are alsoassessed and discussed in details.

  • JOURNAL ARTICLE
    Ng BF, Palacios R, Kerrigan EC, Graham JMR, Hesse H, Ng BF, Palacios R, Kerrigan EC, Graham JMR, Hesse H, Ng BF, Palacios R, Kerrigan EC, Graham JMR, Hesse H, Ng BF, Palacios R, Kerrigan EC, Graham JMR, Hesse H, Ng BF, Palacios R, Kerrigan EC, Graham JMR, Hesse Het al., 2016,

    Aerodynamic load control in horizontal axis wind turbines with combined aeroelastic tailoring and trailing-edge flaps

    , WIND ENERGY, Vol: 19, Pages: 243-263, ISSN: 1095-4244

    Copyright © 2015 John Wiley & Sons, Ltd. This paper presents an aeroservoelastic modeling approach to investigate dynamic load alleviation in large wind turbines with composite blades and trailing-edge aerodynamic surfaces. The tower and rotating blades are modeled using geometrically non-linear composite beams and linearized about reference rotating conditions with potentially arbitrarily large structural displacements. The aerodynamics of the rotor are represented using a linearized unsteady vortex lattice method, and the resulting aeroelastic system is written in a state-space description that is both convenient for model reductions and control design. A linear model of a single blade is then used to design an regulator, capable of providing load reductions of up to 13% in closed loop on the full wind turbine non-linear aeroelastic model. When combined with passive load alleviation through aeroelastic tailoring, dynamic loads can be further reduced to 35%. While the separate use of active flap controls and passive mechanisms for load alleviation has been well-studied, an integrated approach involving the two mechanisms has yet to be fully explored and is the focus of this paper. Finally, the possibility of exploiting torsional stiffness for active load alleviation on turbine blades is also considered.

  • JOURNAL ARTICLE
    Pudjianto D, Castro M, Strbac G, Liu Z, van der Sluis L, Papaefthymiou G, Pudjianto D, Castro M, Strbac G, Liu Z, van der Sluis L, Papaefthymiou G, Pudjianto D, Castro M, Strbac G, Liu Z, van der Sluis L, Papaefthymiou G, Pudjianto D, Castro M, Strbac G, Liu Z, van der Sluis L, Papaefthymiou G, Pudjianto D, Castro M, Strbac G, Liu Z, van der Sluis L, Papaefthymiou Get al., 2016,

    Asymmetric impacts of European transmission network development towards 2050: Stakeholder assessment based on IRENE-40 scenarios

    , ENERGY ECONOMICS, Vol: 53, Pages: 261-269, ISSN: 0140-9883

    © 2014 Elsevier B.V. This paper presents the assessment of stakeholder impacts of European electricity transmission network investments for a set of future system development scenarios. A techno-economic analysis is adopted, which quantifies the economic impacts on different stakeholders including electricity producers, consumers, and network investors, under the future de-carbonisation pathways described in the IRENE-40 scenarios, ranging from 2010 to 2050. To quantify the impact of transmission infrastructure development, for each pathway, two distinct scenarios of future European transmission development are assessed: "low" (no new transmission between 2010 and 2050) and "high" (optimal transmission development between 2010 and 2050 to accommodate the generation pathway).The geographical scope of the analysis covers the EU 27+2 nations. A detailed case study of Spain and France is presented to illustrate the so-called 'asymmetric' impacts towards different stakeholders in different importing and exporting zones. The resulting arbitrage trades shift the market equilibriums, which eventually affect asymmetrically the welfare of stakeholders.

  • JOURNAL ARTICLE
    Strbac G, Kirschen D, Moreno R, 2016,

    Reliability Standards for the Operation and Planning of Future Electricity Networks

    , Foundations and Trends® in Electric Energy Systems, Vol: 1, Pages: 143-219, ISSN: 2332-6557
  • JOURNAL ARTICLE
    Strbac G, Kirschen D, Moreno R, 2016,

    Reliability standards for the operation and planning of future electricity networks

    , Foundations and Trends® in Electric Energy Systems, Vol: 1, Pages: 143-219, ISSN: 2332-6557

    Electricity networks, designed and operated in accordance with the historic deterministic standards, have broadly delivered secure and reliable supplies to customers. A key issue regarding their evolution is how the operation and planning standards should evolve to make efficient use of the existing assets while taking advantage of emerging, non-network (or non-wires) technologies. Deployment of the smart grid will require fundamental changes in the historical principles used for network security in order to ensure that integration of low-carbon generation is undertaken as efficiently as possible through the use of new information and communication technology (ICT), and new flexible network technologies that can maximize utilization of existing electricity infrastructure. These new technologies could reduce network redundancy in providing security of supply by enabling the application of a range of advanced, technically effective, and economically efficient corrective (or post-fault) actions that can release latent network capacity of the existing system. In this context, this paper demonstrates that historical deterministic practices and standards, mostly developed in the 1950s, should be reviewed in order to take full advantage of new emerging technologies and facilitate transition to a smart grid paradigm. This paper also demonstrates that a probabilistic approach to developing future efficient operating and design strategies enabled by new technologies, will appropriately balance network investment against non-network solutions while truly recognizing effects of adverse weather, common-mode failures, high-impact low-probability events, changing market prices for pre- and post-contingency actions, equipment malfunctioning, etc. This clearly requires explicit consideration of the likelihood of various outages (beyond those considered in deterministic studies) and quantification of their impacts on alternative network operation and investment decisions, which canno

  • JOURNAL ARTICLE
    Trovato V, Tindemans SH, Strbac G, Trovato V, Tindemans SH, Strbac G, Trovato V, Tindemans SH, Strbac G, Trovato V, Tindemans SH, Strbac Get al., 2016,

    Leaky storage model for optimal multi-service allocation of thermostatic loads

    , IET GENERATION TRANSMISSION & DISTRIBUTION, Vol: 10, Pages: 585-593, ISSN: 1751-8687

    © The Institution of Engineering and Technology 2016. Collectively, thermostatically controlled loads (TCLs) offer significant potential for short-term demand response. This intrinsic flexibility can be used to provide various ancillary services or to carry out energy arbitrage. This study introduces an aggregate description of the flexibility of a heterogeneous TCL as a leaky storage unit, with associated constraints that are derived from the TCL device parameters and quality of service requirements. In association with a suitable TCL control strategy this enables a straightforward embedding of TCL dynamics in optimisation frameworks. The tools developed are applied to the problem of determining an optimal multi-service portfolio for TCLs. A linear optimisation model is constructed for the optimal simultaneous allocation of frequency services and energy arbitrage. In a case study, optimal service allocations are computed for eight representative classes of cold appliances and the results are validated using simulations of individual refrigerators. Finally, it is demonstrated that clustering of appliances with similar capabilities can significantly enhance the flexibility available to the system.

  • JOURNAL ARTICLE
    Abraham E, Kerrigan EC, Abraham E, Kerrigan EC, Abraham E, Kerrigan ECet al., 2015,

    Lower-Order <formula formulatype="inline"><tex Notation="TeX">$H_{\infty} $</tex></formula> Filter Design for Bilinear Systems With Bounded Inputs

    , IEEE Transactions on Signal Processing, Vol: 63, Pages: 895-906, ISSN: 1053-587X
  • JOURNAL ARTICLE
    Agalgaonkar YP, Pal BC, Jabr RA, Agalgaonkar YP, Pal BC, Jabr RA, Agalgaonkar Y, Pal BC, Jabr RAet al., 2015,

    Stochastic Distribution System Operation Considering Voltage Regulation Risks in the Presence of PV Generation

    , IEEE TRANSACTIONS ON SUSTAINABLE ENERGY, Vol: 6, Pages: 1315-1324, ISSN: 1949-3029

    Variable over voltage, excessive tap counts andvoltage regulator (VR) runaway condition are major operationalchallenges in distribution network while accommodating generationfrom Photovoltaics (PVs). The conventional approach toachieve voltage control based on off-line simulation for voltage setpoint calculation does not consider forecast errors. In this work,a stochastic optimal voltage control strategy is proposed whileconsidering load and irradiance forecast errors. Stochastic operationalrisks such as overvoltage and VR runaway are definedthrough a chance constrained optimization (CCO) problem. Thisclassical formulation to mitigate runaway is further improvedby introducing a stochastic index called the Tap Tail Expectation.Operational objectives such as power losses and excessive tapcount minimization are considered in the formulation. A samplingapproach is proposed to solve the CCO. Along with other voltagecontrol devices, the PV inverter voltage support features arecoordinated. The simulation study is performed using a realisticdistribution system model and practically measured irradianceto demonstrate the effectiveness of the proposed technique.The proposed approach is a useful operational procedure fordistribution system operators. The approach can minimize feederpower losses, avoid voltage violations and alleviate VR runaway.

  • JOURNAL ARTICLE
    Akhtar Z, Chaudhuri B, Hui SYR, Akhtar Z, Chaudhuri B, Hui SYR, Akhtar Z, Chaudhuri B, Hui Set al., 2015,

    Smart loads for voltage control in distribution networks

    , IEEE Transactions on Smart Grid, Vol: PP, Pages: 1-10, ISSN: 1949-3053

    © 2015 IEEE. This paper shows that the smart loads (SLs) could be effective in mitigating voltage problems caused by photovoltaic (PV) generation and electric vehicle (EV) charging in low-voltage (LV) distribution networks. Limitations of the previously reported SL configuration with only series reactive compensator (SLQ) (one converter) is highlighted in this paper. To overcome these limitations, an additional shunt converter is used in back-to-back (B2B) configuration to support the active power exchanged by the series converter, which increases the flexibility of the SL without requiring any energy storage. Simulation results on a typical U.K. LV distribution network are presented to compare the effectiveness of an SL with B2B converters (SLBCs) against an SLQ in tackling under- and over-voltage problems caused by EV or PV. It is shown that SLBCs can regulate the main voltage more effectively than SLQs especially under overvoltage condition. Although two converters are required for each SLBC, it is shown that the apparent power capacity of each converter is required to be significantly less than that of an equivalent SLQ.

  • JOURNAL ARTICLE
    Akhtar Z, Chaudhuri B, Hui SYR, Akhtar Z, Chaudhuri B, Ron Hui SY, Akhtar Z, Chaudhuri B, Ron Hui SY, Akhtar Z, Chaudhuri B, Hui SYRet al., 2015,

    Primary Frequency Control Contribution From Smart Loads Using Reactive Compensation

    , IEEE TRANSACTIONS ON SMART GRID, Vol: 6, Pages: 2356-2365, ISSN: 1949-3053

    © 2015 IEEE. Frequency-dependent loads inherently contribute to primary frequency response. This paper describes additional contribution to primary frequency control based on voltage-dependent noncritical (NC) loads that can tolerate a wide variation of supply voltage. By using a series of reactive compensators to decouple the NC load from the mains to form a smart load (SL), the voltage, and hence the active power of the NC load, can be controlled to regulate the mains frequency. The scope of this paper focuses primarily on reactive compensators for which only the magnitude of the injected voltage could be controlled while maintaining the quadrature relationship between the current and voltage. New control guidelines are suggested. The effectiveness of the SLs in improving mains frequency regulation without considering frequency-dependent loads and with little relaxation in mains voltage tolerance is demonstrated in a case study on the IEEE 37 bus test distribution network. Sensitivity analysis is included to show the effectiveness and limitations of SLs for varying load power factors, proportion of SLs, and system strengths.

  • JOURNAL ARTICLE
    Anagnostou G, Pal BC, Anagnostou G, Pal BC, Anagnostou G, Pal BCet al., 2015,

    Impact of Overexcitation Limiters on the Power System Stability Margin Under Stressed Conditions

    , IEEE Transactions on Power Systems, Vol: 31, Pages: 2327-2337, ISSN: 1558-0679

    This paper investigates the impact of the overexcitation limiters (OELs) on the stability margin of a power system which is operating under stressed conditions. Several OEL modeling approaches are presented and the effect of their action has been examined in model power systems. It is realized that, more often than not, OEL operating status goes undetected by existing dynamic security assessment tools commonly used in the industry. It is found that the identification and accurate representation of OELs lead to significantly different transient stability margins. Unscented Kalman filtering is used to detect the OEL activation events. In the context of stressed system operation, such quantitative assessment is very useful for system control. This understanding is further reinforced through detailed studies in two model power systems.

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