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  • Journal article
    Viola G, Ortega R, Banavar R, Acosta J A, Astolfi Aet al., 2007,

    Total Energy Shaping Control of Mechanical Systems: Simplifying the Matching Equations Via Coordinate Changes

    , IEEE Trans. Automatic Control, Vol: 52, Pages: 1093-1099
  • Journal article
    Goulart PJ, Kerrigan EC, Ralph D, 2007,

    Efficient Robust Optimization for Robust Control with Constraints.

    , Mathematical Programming, Vol: 114, Pages: 115-147, ISSN: 1436-4646

    This paper proposes an efficient computational technique for theoptimal control of linear discrete-time systems subject to bounded disturbanceswith mixed linear constraints on the states and inputs. The problem of computingan optimal state feedback control policy, given the current state, is non-convex.A recent breakthrough has been the application of robust optimizationtechniques to reparameterize this problem as a convex program. While thereparameterized problem is theoretically tractable, the number of variables isquadratic in the number of stages or horizon length N and has no apparentexploitable structure, leading to computational time of O(N6) per iteration ofan interior-point method. We focus on the case when the disturbance set is ∞-norm bounded or the linear map of a hypercube, and the cost function involvesthe minimization of a quadratic cost. Here we make use of state variables toregain a sparse problem structure that is related to the structure of the originalproblem, that is, the policy optimization problem may be decomposed into aset of coupled finite horizon control problems. This decomposition can then be formulated as a highly structured quadratic program, solvable by primaldualinterior-point methods in which each iteration requires O(N3) time. Thiscubic iteration time can be guaranteed using a Riccati-based block factorizationtechnique, which is standard in discrete-time optimal control. Numerical resultsare presented, using a standard sparse primal-dual interior point solver, thatillustrate the efficiency of this approach.
  • Conference paper
    Silva N F, Strbac G, 2007,

    Startegic investment in distribution networks with high penetration of small scale distributed energy resources
  • Conference paper
    Pais da Silva A M, Mohammadu Kairudeen M S, Dragovic J, Djapic P, Strbac G, Allan Ret al., 2007,

    Reliability Evaluation of Distribution Networks and Performance Comparison using Representative Networks
  • Conference paper
    Yates D C, Casson A, Rodriguez-Villegas E, 2007,

    Low Power Technology for Wearable Cognition Systems
  • Journal article
    Rakovic S V, Kerrigan E C, Kouramas K I, Mayne D Qet al., 2007,

    Optimized robust control invariance for linear discrete-time systems: Theoretical foundations

    , Automatica, Vol: 43, Pages: 831-841
  • Journal article
    Rakovic S V, Kerrigan E C, Kouramas K I, Mayne D Qet al., 2007,

    Optimized robust control invariance for linear discrete-time systems: Theoretical foundations

    , Automatica, Vol: 43, Pages: 831-841
  • Journal article
    Kroutikova N, Hernandez-Aramburo CA, Green TC, 2007,

    State-space model of grid-connected inverters under current control mode

    , IET ELECTRIC POWER APPLICATIONS, Vol: 1, Pages: 329-338, ISSN: 1751-8660
  • Conference paper
    Brucoli M, Green TC, 2007,

    Fault behaviour in islanded microgrids

    , 19th International Conference on Electricity Distribution CIRED
  • Conference paper
    Tan C W, Green T C, Hernandez-Aramburo C A, 2007,

    Comparative Study of Perturbation Step-Size for Perturb and Observe Maximum Power Point Tracking Algorithm

    , Pages: 79-84
  • Journal article
    Angeli D, 2007,

    Multistability in systems with counter-clockwise input-output dynamics

    , IEEE Transactions on Automatic Control, Vol: 52, Pages: 596-609, ISSN: 0018-9286
  • Conference paper
    Brucoli M, Green TC, McDonald JDF, 2007,

    Modelling and Analysis of Fault Behaviour of Inverter Microgrids to Aid Future Fault Detection

    , IEEE SoSE Conference
  • Conference paper
    Barnes M, Kondoh J, Asano H, Oyarzabal J, Ventakaramanan G, Lasseter R, Hatziargyriou N, Green TCet al., 2007,

    Real-World MicroGrids: An Overview

    , IEEE SoSE Conference, Pages: 1-8
  • Conference paper
    Barklund EF, Pogaku N, Prodanovic M, Hernandez-Aramburo CA, Green TCet al., 2007,

    Energy Management System with Stability Constraints for Stand-alone Autonomous Microgrid

    , IEEE SoSE Conference
  • Conference paper
    Zolotas AC, Korba P, Chaudhuri B, Jaimoukha IMet al., 2007,

    H2 LMI-based Robust Control for Damping Oscillations in Power Systems

    , Pages: 1-8
  • Journal article
    Brucoli M, Green TC, 2007,

    Fault response of inverter dominated microgrids

    , International Journal of Distributed Energy Resources, Vol: 3, ISSN: 1614-7138
  • Journal article
    Pudjianto D, Ramsay C, Strbac G, 2007,

    Virtual power plant and system integration of distributed energy resources

    , IET Renewable Power Generation, Vol: 1, Pages: 10-16
  • Journal article
    PARISINI T, ZOPPOLI R, 1994,

    NEURAL NETWORKS FOR NONLINEAR STATE ESTIMATION

    , INTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Vol: 4, Pages: 231-248, ISSN: 1049-8923
  • Journal article
    CASALINO G, MINCIARDI R, PARISINI T, 1991,

    DEVELOPMENT OF A NEW SELF-TUNING CONTROL ALGORITHM FOR FINITE AND INFINITE HORIZON QUADRATIC ADAPTIVE OPTIMIZATION

    , INTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Vol: 5, Pages: 405-425, ISSN: 0890-6327
  • Journal article
    Pogaku N, Prodanovic M, Green TC, 2007,

    Modeling, analysis and testing of autonomous operation of an inverter-based microgrid

    , IEEE Transactions on Power Electronics, Vol: 22, Pages: 613-625, ISSN: 1941-0107

    The analysis of the small-signal stability of conventionalpower systems is well established, but for inverter basedmicrogrids there is a need to establish how circuit and controlfeatures give rise to particular oscillatory modes and which ofthese have poor damping. This paper develops the modeling andanalysis of autonomous operation of inverter-based microgrids.Each sub-module is modeled in state-space form and all arecombined together on a common reference frame. The modelcaptures the detail of the control loops of the inverter but not theswitching action. Some inverter modes are found at relatively highfrequency and so a full dynamic model of the network (ratherthan an algebraic impedance model) is used. The complete modelis linearized around an operating point and the resulting systemmatrix is used to derive the eigenvalues. The eigenvalues (termed“modes”) indicate the frequency and damping of oscillatorycomponents in the transient response. A sensitivity analysis is alsopresented which helps identifying the origin of each of the modesand identify possible feedback signals for design of controllersto improve the system stability. With experience it is possible tosimplify the model (reduce the order) if particular modes arenot of interest as is the case with synchronous machine models.Experimental results from a microgrid of three 10-kW invertersare used to verify the results obtained from the model.
  • Journal article
    Black M, Strbac G, 2007,

    Value of bulk energy storage for managing wind power fluctuations

    , IEEE TRANSACTIONS ON ENERGY CONVERSION, Vol: 22, Pages: 197-205, ISSN: 0885-8969
  • Journal article
    Prodanovic M, De Brabandere K, Van den Keybus J, Green TC, Driesn Jet al., 2007,

    Harmonic and reactive power compensation as ancillary services in inverter-based distributed generation

    , IET - Generation, Transmission and Distribution, Vol: 1, Pages: 432-438

    The introduction of distributed generation, DG, into low-voltage (LV) networks opens up the possibility of supplying ancillary services to aid network management and to maintain powerquality. DG itself can cause voltage magnitude difficulties when injecting real power into networks with high R/X ratios, but control of reactive power injection can help overcome this. Continuous control and support only at the voltage limit conditions (to avoid unnecessary reactive power flows in normal conditions) are explored. Relatively high-impedance LV networks are prone to harmonic distortion from nonlinear loads. A variety of control methods that emphasise either harmonic-line flows or local-voltage distortion are examined, and a compromise method based on resistance emulation is shown to be effective. Experimental results from a single-phase laboratory network and 2 kVA inverter are used to illustrate how these additional control functions can be integrated into the existing control scheme for real-power management. Decomposition of observed voltages and currents into harmonic terms that are phase synchronised to the grid voltage is a challenge in real-time systems. Kalman observers are used to achieve this with an additional advantage of avoiding explicit phase-locking while producing quadrature components useful in instantaneous calculation of reactive power and in providing feed-forward compensation terms.
  • Journal article
    De Leenheer P, Sontag ED, Angeli D, 2007,

    Monotone chemical reaction networks

    , Journal of Mathematical Chemistry, Vol: 41, Pages: 295-314
  • Journal article
    Bianchini G, Falugi P, Tesi A, Vicino Aet al., 2007,

    A convex lower bound for the real l<sub>2</sub> parametric stability margin of linear control systems with restricted complexity controllers

    , IEEE TRANSACTIONS ON AUTOMATIC CONTROL, Vol: 52, Pages: 514-520, ISSN: 0018-9286
  • Journal article
    Jabr R A, Pal B C, 2007,

    A Conic Programming Approach for Static Voltage Stability Analysis in Radial Networks

    , IET Generation Transmission & Distribution, Pages: 203-208

    That the problem of computing the capacity limit of a radial distribution system can be formulated as a second-order cone program is shown. The implications of the conic programming formulation are 2-fold. First, the load capability of the radial system can be obtained using existing efficient implementations of polynomial time interior-point algorithms, thus avoiding the need for running a sequence of load flow solutions. Secondly, the conic objective function yields a voltage stability indicator (SI). This indicator quantifies the maximum percentage by which the current load profile can be uniformly increased before voltage collapse occurs. The proposed method is validated by computing the load capability and voltage SIs of 11 different distribution systems. Comparisons are carried out with five previously published voltage SIs
  • Journal article
    Astolfi A, Karagiannis D, Ortega R, 2007,

    Stabilization of uncertain nonlinear systems via Immersion and Invariance

    , European Journal of Control, Vol: 13, Pages: 204-220
  • Journal article
    Astolfi A, 2007,

    A remark on an example by Teel-Hespanha with applications to cascaded systems

    , IEEE TRANSACTIONS ON AUTOMATIC CONTROL, Vol: 52, Pages: 289-293, ISSN: 0018-9286
  • Journal article
    Gross R, Heptonstall P, Leach M, Anderson D, Green TC, Skea Jet al., 2007,

    Renewables and the grid: understanding intermittency

    , Proceedings of the Institution of Civil Engineers - Energy, Vol: 160, Pages: 31-41

    This paper reviews the key issues and findings of the UK Energy Research Centre report on the costs and impacts of intermittent or variable renewable electricity-generating technologies. The relevant principles of managing electricity networks are examined and aspects that change when significant intermittent generation is added are analysed.The impacts and costs of intermittent generators can be quantified only in the context of the characteristics of the system of which they form part. The principal reasons why these impacts differ from one system to another are examined and explained. The evidence for likely impactsand costs in the UK, at intermittent penetration levels up to 20% of total electricity supplied, is analysed. The two main categories of impact are on system balancing and system reliability, and costs are quantified for these factors.Estimates are in the range of an additional £2–3/MWh for system balancing and £3–5/MWh for system reliability.
  • Conference paper
    Astolfi A, Karagiannis D, Orgtega R, 2007,

    Stabilization of uncertain nonlinear systems via immersion and invariance

    , Pages: 204-220, ISSN: 0947-3580

    This paper presents a method for designing asymptotically stabilising and adaptive convtrol laws for uncertain nonlinear systems. The method relies upon the notions of system immersion and manifold invariance and, in principle, does not require the knowledge of a (control) Lyapunov function. The construction of the stabilising control laws resembles the procedure used in nonlinear regulator theory to derive the (invariant) output-zeroing manifold and its friend, and is well suited, for instance, in situations where we know a stabilising controller of a nominal reduced-order model, which we would like to robustify with respect to higher-order dynamics. In adaptive control problems the method yields stabilising schemes that counter the effect of the uncertain parameters adopting a robustness perspective. This is in contrast with most existing adaptive designs that (relying on certain matching conditions) treat these terms as disturbances to be rejected. The construction does not invoke certainty equivalence, nor requires a linear parameterisation. Furthermore, viewed from a Lyapunov perspective, it provides a procedure to add cross terms between the parameter estimates and the plant states. To illustrate the concepts presented in this paper we introduce several academic and physical examples, including a mechanical system with flexibility modes, an electromechanical system with parasitic actuator dynamics, and an adaptive, nonlinearly parameterised, visual servoing problem. © 2007 EUCA.
  • Journal article
    Djapic P, Ramsay C, Pudjianto D, Strbac G, Mutale J, Jenkins N, Allan Ret al., 2007,

    Taking an active approach

    , IEEE POWER & ENERGY MAGAZINE, Vol: 5, Pages: 68-77, ISSN: 1540-7977

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