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  • Journal article
    Strbac G, Pollitt M, Konstantinidis CV, Konstantelos I, Moreno R, Newbery D, Green Ret al., 2014,

    Electricity transmission arrangements in Great Britain: Time for change?

    , Energy Policy, Vol: 73, Pages: 298-311, ISSN: 0301-4215

    In Great Britain (GB) and across Europe significant investment in electricity transmission is expected over the coming years as decarbonisation and market integration efforts are intensified. However, there is also significant uncertainty with the amount, location and timing of new generation connection, which in turn will drive the transmission investment needs. Given the absence of efficient market design, we identify three key areas of concern with the current transmission investment arrangements: (i) a mis-aligned incentives framework for transmission investment and operation; (ii) lack of coordination of investment and operation; and (iii) conflicts of interest. We then propose three options for future evolution of transmission regimes, which cover the full spectrum of institutional arrangements with respect to transmission planning and delivery, i.e. how and who plans, owns, builds and operates the transmission system. For each option we present: key characteristics; evolution of the current regimes; the ability of the option to address the concerns; and key strengths and weaknesses. Overall, we conclude in the case of GB (this conclusion could be extended to other European countries) that the most appropriate option would be that of an Independent System Operator (ISO) who would be responsible for planning and operating the transmission system.
  • Journal article
    Schiffer J, Ortega R, Astolfi A, Raisch J, Sezi Tet al., 2014,

    Conditions for stability of droop-controlled inverter-based microgrids

    , Automatica, Vol: 50, Pages: 2457-2469, ISSN: 0005-1098

    We consider the problem of stability analysis for droop-controlled inverter-based microgrids with meshed topologies. The inverter models include variable frequencies as well as voltage amplitudes. Conditions on the tuning gains and setpoints for frequency and voltage stability, together with desired active power sharing, are derived in the paper. First, we prove that for all practical choices of these parameters global boundedness of trajectories is ensured. Subsequently, assuming the microgrid is lossless, a port-Hamiltonian description is derived, from which sufficient conditions for stability are given. Finally, we propose for generic lossy microgrids a design criterion for the controller gains and setpoints such that a desired steady-state active power distribution is achieved. The analysis is validated via simulation on a microgrid based on the CIGRE (Conseil International des Grands Réseaux Electriques) benchmark medium voltage distribution network.
  • Journal article
    Papadaskalopoulos D, Pudjianto D, Strbac G, 2014,

    Decentralized Coordination of Microgrids With Flexible Demand and Energy Storage

    , IEEE TRANSACTIONS ON SUSTAINABLE ENERGY, Vol: 5, Pages: 1406-1414, ISSN: 1949-3029
  • Journal article
    Egea-Alvarez A, Junyent-Ferre A, Bergas-Jane J, Bianchi FD, Gomis-Bellmunt Oet al., 2014,

    Control of a wind turbine cluster based on squirrel cage induction generators connected to a single VSC power converter

    , INTERNATIONAL JOURNAL OF ELECTRICAL POWER & ENERGY SYSTEMS, Vol: 61, Pages: 523-530, ISSN: 0142-0615
  • Journal article
    Li S, Hui SYR, 2014,

    Self-Configurable Current-Mirror Circuit With Short-Circuit and Open-Circuit Fault Tolerance for Balancing Parallel Light-Emitting Diode (LED) String Currents

    , IEEE TRANSACTIONS ON POWER ELECTRONICS, Vol: 29, Pages: 5498-5507, ISSN: 0885-8993
  • Journal article
    Chang H, Krieger A, Astolfi A, Pistikopoulos ENet al., 2014,

    Robust multi-parametric model predictive control for LPV systems with application to anaesthesia

    , JOURNAL OF PROCESS CONTROL, Vol: 24, Pages: 1538-1547, ISSN: 0959-1524
  • Conference paper
    Carmichael R, Schofield J, Bilton M, Ozaki R, Strbac Get al., 2014,

    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
  • Book
    Chaudhuri N, Chaudhuri B, Majumder R, Yazdani Aet al., 2014,

    Multi-terminal Direct-Current Grids

    , Publisher: Wiley IEEE, ISBN: 9781118729106

    Commercial unavailability of efficient DC side fault current interruption technology for conventional voltage sourced converter systems This book addresses the first issue in details by presenting a comprehensive modeling, analysis and ...
  • Report
    Konstantelos I, Sun M, Strbac G, 2014,

    Quantifying demand diversity of households

    , Quantifying demand diversity of households, Publisher: Imperial College London
  • Journal article
    Hui SYR, Zhong W, Lee CK, 2014,

    A Critical Review of Recent Progress in Mid-Range Wireless Power Transfer

    , IEEE TRANSACTIONS ON POWER ELECTRONICS, Vol: 29, Pages: 4500-4511, ISSN: 0885-8993
  • Journal article
    Ng WM, Zhang C, Lin D, Hui SYRet al., 2014,

    Two- and Three-Dimensional Omnidirectional Wireless Power Transfer

    , IEEE TRANSACTIONS ON POWER ELECTRONICS, Vol: 29, Pages: 4470-4474, ISSN: 0885-8993
  • Journal article
    Chaillet A, Angeli D, Ito H, 2014,

    Strong iISS is preserved under cascade interconnection

    , AUTOMATICA, Vol: 50, Pages: 2424-2427, ISSN: 0005-1098
  • Journal article
    Chang HJ, Moog CH, Astolfi A, Rivadeneira PSet al., 2014,

    A control systems analysis of HIV prevention model using impulsive input

    , BIOMEDICAL SIGNAL PROCESSING AND CONTROL, Vol: 13, Pages: 123-131, ISSN: 1746-8094
  • Journal article
    Chaillet A, Angeli D, Ito H, 2014,

    Combining iISS and ISS With Respect to Small Inputs: The Strong iISS Property

    , IEEE TRANSACTIONS ON AUTOMATIC CONTROL, Vol: 59, Pages: 2518-2524, ISSN: 0018-9286
  • Report
    Carmichael R, Schofield J, Woolf M, Bilton M, Ozaki R, Strbac Get al., 2014,

    Residential consumer attitudes to time-varying pricing

    , Report A2 for the 'Low Carbon London' LCNF project, London, Publisher: Imperial College, A2
  • Journal article
    Chaudhuri NR, Lee CK, Chaudhuri B, Hui SYRet al., 2014,

    Dynamic Modeling of Electric Springs

    , IEEE TRANSACTIONS ON SMART GRID, Vol: 5, Pages: 2450-2458, ISSN: 1949-3053
  • Report
    Bilton M, Carmichael R, Whitney A, Dragovic J, Schofield J, Woolf M, Strbacet al., 2014,

    Accessiblity and validity of smart meter data

    , Report C5 for the “Low Carbon London” LCNF project: Imperial College London, C5
  • Journal article
    Sanz IM, Chaudhuri B, Strbac G, 2014,

    Inertial Response From Offshore Wind Farms Connected Through DC Grids

    , IEEE Transactions on Power Systems, Vol: 30, Pages: 1518-1527, ISSN: 0885-8950
  • Conference paper
    Falugi P, 2014,

    Model predictive Control: a passive scheme

    , 19th IFAC World Congress, Publisher: International Federation of Automatic Control, Pages: 1017-1022

    This note studies the formulation of model predictive control exploiting passivity properties. The introduction of passive constraints in model predictive control schemes is particularly appealing since robustness against model uncertainty is inherently guaranteed. The potential of the discussed control scheme is shown on the regulation problem of a robot manipulator.
  • Journal article
    Yan S, Tan S-C, Lee C-K, Chaudhuri B, Hui SYRet al., 2014,

    Electric Springs for Reducing Power Imbalance in Three-Phase Power Systems

    , IEEE Transactions on Power Electronics, Vol: 30, Pages: 3601-3609, ISSN: 0885-8993
  • Conference paper
    Ye Y, Papadaskalopoulos D, Strbac G, 2014,

    Pricing Flexible Demand Non-Convexities in Electricity Markets

    , 18th Power Systems Computation Conference (PSCC), Publisher: IEEE, Pages: 1-7, ISSN: 1944-9933

    Uniform marginal prices cannot generally support competitive equilibrium solutions in markets with non-convexities and yield schedules' inconsistency and surplus sub-optimality effects. Previous work has identified non-convexities associated with the generation side of electricity markets and proposed a generalized uplift approach to eliminate these effects. This paper examines the above issues from the perspective of the flexible demand (FD) side. FD non-convexities are identified, including its ability to forgo demand activities and minimum power levels, and resulting inconsistency and surplus sub-optimality effects are demonstrated through simple examples. Generalized uplift functions for FD participants are proposed, including quadratic pricing terms to limit their tendency to concentrate at the lowest-priced periods, and binary terms associated with their ability to forgo activities. Finally, a new rule is proposed for the equitable distribution of the total surplus loss among the market participants. These contributions are supported by case studies on a market with a day-ahead horizon and hourly resolution.
  • Journal article
    Tortelli OL, Laurenco EM, Garcia AV, Pal BCet al., 2014,

    Fast Decoupled Power Flow to Emerging Distribution Systems via Complex pu Normalization

    , IEEE Transactions on Power Systems, Vol: PP, Pages: 1-8, ISSN: 0885-8950

    This paper proposes a generalized approach of the per unit normalization, named complex per unit normalization (cpu), to improve the performance of fast decoupled power flow methods applied to emerging distribution networks. The proposed approach takes into account the changes envisaged and also already faced by distribution systems, such as high penetration of generation sources and more interconnection between feeders, while considering the typical characteristics of distribution systems, as the high R/ X ratios. These characteristics impose difficulties on the performance of both backward-forward sweep and decoupled-based power flow methods. The cpu concept is centred on the use of a complex volt-ampere base, which overcomes the numerical problems raised by the high R/ X ratios of distribution feeders. As a consequence, decoupled power flow methods can be efficiently applied to distribution system analysis. The performance of the proposed technique and the simplicity of adapting it to existing power flow programs are addressed in the paper. Different distribution network configurations and load conditions have been used to illustrate and evaluate the use of cpu.
  • Journal article
    Chen HT, Lin DY, Tan SC, Hui SYRet al., 2014,

    Chromatic, photometric and thermal modeling of LED systems with nonidentical LED devices

    , IEEE Transactions on Power Electronics, Vol: 29, Pages: 6636-6647, ISSN: 0885-8993

    With the emergence of new color-mixing LED systems based on LED devices of different color temperatures, the need for a new modeling technique for LED systems with nonidentical LED devices becomes imminent. This paper presents a modeling technique for LED systems with LED arrays comprising nonidentical LED devices that have nonidentical optical-thermal-electrical properties. Based on a general 3-D photo-electro-thermal LED node model, LED devices of different kinds can be arranged in various array forms according to their system construction and design. By linking the system matrix to the correlated-colorerature prediction, the proposed modeling technique provides an accurate prediction of the temperature distribution, luminous flux, and correlated color temperature of the LED systems. The temperature distribution and light output of the LED systems have been measured using an infrared imaging system and a spectrophotocolorimeter with an integrating sphere. The modeling technique has been successfully demonstrated and experimentally verified on several LED systems comprising nonidentical LED devices. It is particularly useful as a modeling tool to study new color-mixing LED systems based on different types of LED devices. © 2014 IEEE.
  • Journal article
    Lueth T, Merlin MMC, Green TC, Hassan F, Barker CDet al., 2014,

    High-frequency operation of a DC/AC/DC system for HVDC applications

    , IEEE Transactions on Power Electronics, Vol: 29, Pages: 4107-4115, ISSN: 0885-8993

    Voltage ratings for HVdc point-to-point connections are not standardized and tend to depend on the latest available cable technology. DC/DC conversion at HV is required for interconnection of such HVdc schemes as well as to interface dc wind farms. Modular multilevel voltage source converters (VSCs), such as the modular multilevel converter (MMC) or the alternate arm converter (AAC), have been shown to incur significantly lower switching losses than previous two- or three-level VSCs. This paper presents a dc/ac/dc system using a transformer coupling two modular multilevel VSCs. In such a system, the capacitors occupy a large fraction of the volume of the cells but a significant reduction in volume can be achieved by raising the ac frequency. Using high frequency can also bring benefits to other passive components such as the transformer but also results in higher switching losses due to the higher number of waveform steps per second. This leads to a tradeoff between volume and losses which has been explored in this study and verified by simulation results with a transistor level model of 30-MW case study. The outcome of the study shows that a frequency of 350 Hz provides a significant improvement in volume but also a penalty in losses compared to 50 Hz.
  • Journal article
    Casagrande D, Astolfi A, Langarica D, Ortega Ret al., 2014,

    Solution to the multi-machine transient stability problem and simulated validation in realistic scenarios

    , IET GENERATION TRANSMISSION & DISTRIBUTION, Vol: 8, Pages: 1392-1405, ISSN: 1751-8687
  • Journal article
    Wu P, Bai F, Xue Q, Liu X, Hui SYRet al., 2014,

    Use of Frequency-Selective Surface for Suppressing Radio-Frequency Interference from Wireless Charging Pads

    , IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, Vol: 61, Pages: 3969-3977, ISSN: 0278-0046
  • Conference paper
    Mylvaganam T, Bauso D, Astolfi A, 2014,

    Mean-field games and two-point boundary value problems

    , Conference on Decision and Control
  • Journal article
    Ariff MAM, Pal BC, Singh AK, 2014,

    Estimating Dynamic Model Parameters for Adaptive Protection and Control in Power System

    , IEEE Transactions on Power Systems, ISSN: 0885-8950

    This paper presents a new approach in estimating important parameters of power system transient stability model such as inertia constant H and direct axis transient reactance x′d in real time. It uses a variation of unscented Kalman filter (UKF) on the phasor measurement unit (PMU) data. The accurate estimation of these parameters is very important for assessing the stability and tuning the adaptive protection system on power swing relays. The effectiveness of the method is demonstrated in asimulated data from 16-machine 68-bus system model. The paper also presents the performance comparison between the UKF and EKF method in estimating the parameters. The robustness of method is further validated in the presence of noise that is likely to be in the PMU data in reality.
  • Conference paper
    Jiang J, Astolfi A, 2014,

    Output-Feedback Shared-Control for Fully Actuated Linear Mechanical Systems

    , American Control Conference, Publisher: IEEE, Pages: 335-340, ISSN: 0743-1619

    This paper presents an output feedback shared-control algorithm for fully-actuated, linear, mechanical systems. The feasible configurations of the system are described by a group of linear inequalities which characterize a convex admissible set. The properties of the shared-control algorithm are established with a Lyapunov-like analysis. Simple numerical examples demonstrate the effectiveness of the strategy.
  • Journal article
    Li S, Chen H, Tan SC, Hui SY, Waffenschmidt Eet al., 2014,

    Power flow analysis and critical design issues of retrofit Light-Emitting Diode (LED) light bulb

    , IEEE Transactions on Power Electronics, Vol: 30, Pages: 3830-3840, ISSN: 0885-8993

    For retrofit applications, some high-brightness light-emitting diode (LED) products have the same form factor restrictions as existing incandescent light bulbs. Such form factor constraints may restrict the design and optimal performance of the LED technology. In this paper, some critical design issues for commercial LED bulbs designed for replacing E27 incandescent lamps are quantitatively analyzed. The analysis involves power audits on such densely packed LED systems so that the amounts of power consumption in: 1) the LED wafer; 2) the phosphor coating; and 3) the lamp translucent cover are quantified. The outcomes of such audits enable R&D engineers to identify the critical areas that need further improvements in a compact LED bulb design. The strong dependence of the luminous output of the compact LED bulb on ambient temperature is also highlighted.

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