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  • Journal article
    Gavriel C, Vinter RB, 2014,

    Second Order Sufficient Conditions for Optimal Control Problems with Non-unique Minimizers: An Abstract Framework

    , Applied Mathematics and Optimization, Vol: 70, Pages: 411-442, ISSN: 1432-0606

    Standard second order sufficient conditions in optimal control theory provide not only the information that an extremum is a weak local minimizer, but also tell us that the extremum is locally unique. It follows that such conditions will never cover problems in which the extremum is continuously embedded in a family of constant cost extrema. Such problems arise in periodic control, when the cost is invariant under time translations, in shape optimization, where the cost is invariant under Euclidean transformations (translations and rotations of the extremal shape), and other areas where the domain of the optimization problem does not really comprise elements in a linear space, but rather an equivalence class of such elements. We supply a set of sufficient conditions for minimizers that are not locally unique, tailored to problems of this nature. The sufficient conditions are in the spirit of earlier conditions for ‘non-isolated’ minima, in the context of general infinite dimensional nonlinear programming problems provided by Bonnans, Ioffe and Shapiro, and require coercivity of the second variation in directions orthogonal to the constant cost set. The emphasis in this paper is on the derivation of directly verifiable sufficient conditions for a narrower class of infinite dimensional optimization problems of special interest. The role of the conditions in providing easy-to-use tests of local optimality of a non-isolated minimum, obtained by numerical methods, is illustrated by an example in optimal control.
  • Journal article
    Vinter RB, 2014,

    The Hamiltonian Inclusion for Nonconvex Velocity Sets

    , SIAM Journal on Control and Optimization, Vol: 52, Pages: 1237-1250, ISSN: 1095-7138

    Since Clarke's 1973 proof of the Hamiltonian inclusion for optimal control problems with convex velocity sets, there has been speculation (and, more recently, speculation relating to a stronger, partially convexified version of the Hamiltonian inclusion) as to whether these necessary conditions are valid in the absence of the convexity hypothesis. The issue was in part resolved by Clarke himself when, in 2005, he showed that $L^{\infty}$ local minimizers satisfy the Hamiltonian inclusion. In this paper it is shown, by counterexample, that the Hamiltonian inclusion (and so also the stronger partially convexified Hamiltonian inclusion) are not in general valid for nonconvex velocity sets when the local minimizer in question is merely a $W^{1,1}$ local minimizer, not an $L^{\infty}$ local minimizer. The counterexample demonstrates that the need to consider $L^{\infty}$ local minimizers, not $W^{1,1}$ local minimizers, in the proof of the Hamiltonian inclusion for nonconvex velocity sets is fundamental, not just a technical restriction imposed by currently available proof techniques. The paper also establishes the validity of the partially convexified Hamiltonian inclusion for $W^{1,1}$ local minimizers under a normality assumption, thereby correcting earlier assertions in the literature.
  • Journal article
    Scarciotti G, Astolfi A, 2014,

    Approximate finite-horizon optimal control for input-affine nonlinear systems with input constraints

    , Journal of Control and Decision, Vol: 1, Pages: 149-165, ISSN: 2330-7706

    The finite-horizon optimal control problem with input constraints consists in controlling the state of a dynamical system over a finite time interval (possibly unknown) minimising a cost functional, while satisfying hard constraints on the input. In this framework, the minimum-time optimal control problem and some related problems are of interest for both theory and applications. For linear systems, the solution of the problem often relies upon the use of bang-bang control signals. For nonlinear systems, the “shape” of the optimal input is in general not known. The control input can be found solving a Hamilton–Jacobi–Bellman (HJB) partial differential equation (PDE): it typically consists of a combination of bang-bang controls and singular arcs. In this paper, a methodology to approximate the solution of the HJB PDE is proposed. This approximation yields a dynamic state feedback law. The theory is illustrated by means of two examples: the minimum-time optimal control problem for an industrial wastewater treatment plant and the Goddard problem, i.e. a maximum-range optimal control problem.
  • Journal article
    Carvalho NB, Georgiadis A, Costanzo A, Rogier H, Collado A, Angel Garcia J, Lucyszyn S, Mezzanotte P, Kracek J, Masotti D, Soares Boaventura AJ, Ruiz Lavin MDLN, Pinuela M, Yates DC, Mitcheson PD, Mazanek M, Pankrac Vet al., 2014,

    Wireless Power Transmission: R&D Activities Within Europe

    , IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, Vol: 62, Pages: 1031-1045, ISSN: 0018-9480
  • Journal article
    Wan K-C, Xue Q, Liu X, Hui SYRet al., 2014,

    Passive Radio-Frequency Repeater for Enhancing Signal Reception and Transmission in a Wireless Charging Platform

    , IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, Vol: 61, Pages: 1750-1757, ISSN: 0278-0046
  • Journal article
    Pin G, Parisini T, 2014,

    On the Robustness of Nominal Nonlinear Minimum-Time Control and Extension to Non-Robustly Controllable Target Sets

    , IEEE TRANSACTIONS ON AUTOMATIC CONTROL, Vol: 59, Pages: 863-875, ISSN: 0018-9286
  • Journal article
    Rogers DJ, Green TC, Silversides RW, 2014,

    A Low-Wear Onload Tap Changer Diverter Switch for Frequent Voltage Control on Distribution Networks

    , IEEE TRANSACTIONS ON POWER DELIVERY, Vol: 29, Pages: 860-869, ISSN: 0885-8977
  • Conference paper
    Bauso D, Mylvaganam T, Astolfi A, 2014,

    A Two-Point Boundary Value Formulation of a Mean-Field Crowd-Averse Game

    , IFAC World Congress
  • Book chapter
    Evangelou SA, Tomas-Rodriguez M, 2014,

    Motorcycle Dynamic Modes and Passive Steering Compensation

    , Modelling, Simulation and Control of Two-Wheeled Vehicles, Pages: 221-241

    This chapter introduces the main characteristics of motorcycle oscillatory modes and then discusses how their damping can be increased by employing steering compensation. Weave mode is a fishtailing-type motion involving yaw and roll of the motorcycle body and steering system oscillations. Wobble mode is a steering oscillation that is reminiscent of the supermarket cart front-wheel caster shimmy. The chapter describes a high-fidelity motorcycle model that is used to illustrate quantitatively the characteristics of the oscillatory modes and the influence of steering damping on machine stability. A mathematical model is used to analyse and illustrate the behaviour of motorcycles. This model takes into account the aerodynamic forces and moments, which are proportional to the square of the speed. The chapter explains a design methodology for steering compensation that improves modal damping. Finally, it provides an analysis of burst oscillations followed by a design of steering compensation to suppress these oscillations.
  • Conference paper
    Thommyppillai M, Evangelou S, Sharp RS, 2014,

    Towards a practical virtual racing-car driver

    , Pages: 4943-4948

    Fundamental approaches to modelling the control of a car by a driver are reviewed briefly. The context of the work presented is explained. Then, previous research on the application of optimal linear preview control to aspects of driving road vehicles is extended. This prior research treated the tracking of a roadway by a vehicle and driver at constant forward speed and the tracking of a speed demand while running straight. The two previously separate problems are combined, so that longitudinal and lateral path demands are considered in parallel. A new feature is that low-pass filters are included in the driver modelling, to represent driver bandwidth limitations. This feature enables the finding of the influence of the driver's control bandwidth on the optimal strategies. A new optimal preview control toolbox is employed for the computations. A simulation of the virtual driver-controlled car is shown to demonstrate the closed-loop system following longitudinal and lateral position demands.
  • Conference paper
    Angeli D, 2014,

    A tutorial on chemical reaction networks dynamics

    , Pages: 649-657

    Chemical Reaction Networks (CRN for short) can be effectively modeled by means of nonlinear, parameter-dependent systems of ordinary differential equations. The uncertain knowledge of parameters makes for the need of qualitative tools which relate structure and dynamics of such nonlinear systems. We present an account of different results which allow to claim properties such as global asymptotic stability, persistence, monotonicity and existence of a unique equilibrium on the basis of graphical representations of the network.
  • Journal article
    Ahmed S, Kerrigan EC, 2014,

    Suboptimal predictive control for satellite detumbling

    , Journal of Guidance Control and Dynamics, Vol: 37, Pages: 850-859, ISSN: 1533-3884

    Rate damping in the initial acquisition phase of a magnetically controlled small satellite is a big challenge for the control system. In this phase, the main difficulties are dynamic nonlinearities due to high body rates, time-varying control due to the change in Earth’s magnetic field, inherent underactuation, and constraints on available power. The control system is required to minimize the detumbling time with minimal use of onboard resources. In comparison to the existing control techniques used in the initial acquisition phase, predictive control can be considered a suitable choice for handling such conflicting objectives in the presence of constraints. In this work, performance of two existing nonlinear model predictive control schemes that guarantee closed-loop stability are analyzed. Nonlinear model predictive control gives improved performance by reducing the detumbling time compared to classical control techniques based on the rate of change of Earth’s magnetic field; however, the computational requirements are high. Furthermore, it is demonstrated that, when the body rates increase, the computational burden of nonlinear model predictive control to reach an optimal point becomes prohibitively large. For these situations, an algorithm is presented that allows early termination of the optimizer by imposing an additional constraint on the cost reduction. The early termination criteria of the optimizer can be chosen based on the available computational resources. The imposed cost reduction constraint also helps in further reducing the detumbling time. Extensive numerical simulations show that the presented algorithm works well in practice for a good range of initial body rates.
  • Conference paper
    kuenzel, Puthenpurayil Kunjumuhammed L, pal, Erlich Iet al., 2014,

    Impact of wakes on wind farm inertial response

    , IEEE PES General Meeting | Conference & Exposition, 2014
  • Journal article
    Pudjianto D, Aunedi M, Djapic P, Strbac Get al., 2014,

    Whole-systems assessment of the value of energy storage in low-carbon electricity systems

    , IEEE Transactions on Smart Grid, Vol: 5, Pages: 1098-1109, ISSN: 1949-3061

    Energy storage represents one of the key enabling technologies to facilitate an efficient system integration of intermittent renewable generation and electrified transport and heating demand. This paper presents a novel whole-systems approach to valuing the contribution of grid-scale electricity storage. This approach simultaneously optimizes investment into new generation, network and storage capacity, while minimising system operation cost, and also considering reserve and security requirements. Case studies on the system of Great Britain (GB) with high share of renewable generation demonstrate that energy storage can simultaneously bring benefits to several sectors, including generation, transmission and distribution, while supporting real-time system balancing. The analysis distinguishes between bulk and distributed storage applications, while also considering the competition against other technologies, such as flexible generation, interconnection and demand-side response.
  • Journal article
    Singh A, Pal BC, 2014,

    Decentralized Dynamic State Estimation in Power Systems Using Unscented Transformation

    , IEEE Transactions on Power Systems, Vol: 29, Pages: 794-804, ISSN: 0885-8950

    This paper proposes a decentralized algorithm for real-time estimation of the dynamic states of a power system. The scheme employs phasor measurement units (PMUs) for the measurement of local signals at each generation unit, and subsequent state estimation using unscented Kalman filtering (UKF). The novelty of the scheme is that the state estimation at one generation unit is independent from the estimation at other units, and therefore the transmission of remote signals to a central estimator is not required. This in turn reduces the complexity of each distributed estimator, and makes the estimation process highly efficient, accurate and easily implementable. The applicability of the proposed algorithm has been thoroughly demonstrated on a representative model.
  • Journal article
    Chen H, Hui SYR, 2014,

    Dynamic prediction of correlated color temperature and color rendering Index of phosphor-coated white light-emitting diodes

    , IEEE Transactions on Industrial Electronics, Vol: 61, Pages: 784-797, ISSN: 0278-0046

    Light-emitting diode (LED) technology is a multidisciplinary subject that involves photometry, electric power, heat, and chromaticity which are interdependent on one another. So far, the photoelectrothermal (PET) theory has linked up the first three aspects. This research includes chromaticity into the dynamic PET theory so that even the correlated color temperature (CCT) and color rendering index (CRI) of phosphor-coated white LEDs can be dynamically predicted, thus overcoming the low bandwidth problem of some light measurement equipment. This dynamic modeling of CCT and CRI has been verified with favorable agreements between theoretical predictions and measurements of several LED samples. The outcome of this project offers a new research and development tool for practicing LED system designers to predict the instantaneous variations of CCT and CRI when the power varies in a LED system.
  • Journal article
    Merlin MMC, Green TC, Mitcheson PD, Trainer DR, Critchley R, Crookes W, Hassan Fet al., 2014,

    The Alternate Arm Converter: A New Hybrid Multilevel Converter With DC-Fault Blocking Capability

    , IEEE Transactions on Power Delivery, Vol: 29, Pages: 310-317, ISSN: 0885-8977

    This paper explains the working principles, supported by simulation results, of a new converter topology intended for HVDC applications, called the alternate arm converter (AAC). It is a hybrid between the modular multilevel converter, because of the presence of H-bridge cells, and the two-level converter, in the form of director switches in each arm. This converter is able to generate a multilevel ac voltage and since its stacks of cells consist of H-bridge cells instead of half-bridge cells, they are able to generate higher ac voltage than the dc terminal voltage. This allows the AAC to operate at an optimal point, called the “sweet spot,” where the ac and dc energy flows equal. The director switches in the AAC are responsible for alternating the conduction period of each arm, leading to a significant reduction in the number of cells in the stacks. Furthermore, the AAC can keep control of the current in the phase reactor even in case of a dc-side fault and support the ac grid, through a STATCOM mode. Simulation results and loss calculations are presented in this paper in order to support the claimed features of the AAC.
  • Journal article
    Zhang Z, Jaimoukha IM, 2014,

    On-line fault detection and isolation for linear discrete-time uncertain systems

    , Automatica, Vol: 50, Pages: 513-518, ISSN: 0005-1098

    This work proposes a robust fault detection and isolation (FDI) scheme for linear discrete-time systems subject to faults, bounded additive disturbances and norm-bounded structured uncertainties. FDI is achieved by computing, on-line, upper and lower bounds on the fault signal such that a fault is regarded as having occurred when its upper bound is smaller than zero or lower bound is larger than zero. Linear Matrix Inequality (LMI) optimization techniques are used to obtain the bounds. Furthermore, a subsequent-state-estimation technique, together with an estimation horizon update procedure, is proposed, which allows the on-line FDI process to be repeated in a moving horizon procedure. Theapproach is also extended to solve the fault detection (FD) problem of obtaining lower bounds on the total fault signal energy within the estimation horizon. The scheme gives the best estimates of the fault signals given the information available and is sufficiently flexible to incorporate other information that may be available, such as bounds on the disturbance energy. Thus our scheme is immune to false alarms if the system and disturbance are within the uncertainty description. Moreover, we propose a new robustness result to obtain the bounds, which is an extension of current techniques for handling model uncertainties.Finally, the approach is verified using two numerical examples.
  • Journal article
    Ionescu TC, Astolfi A, Colaneri P, 2014,

    Families of moment matching based, low order approximations for linear systems

    , SYSTEMS & CONTROL LETTERS, Vol: 64, Pages: 47-56, ISSN: 0167-6911
  • Journal article
    Lawson J, Pinuela M, Yates DC, Lucyszyn S, Mitcheson PDet al., 2014,

    Long range inductive power transfer system

    , Journal of Physics : Conference Series, Vol: 476, Pages: 1-6, ISSN: 1742-6588

    We report upon a recently developed long range inductive power transfer system (IPT) designed to power remote sensors with mW level power consumption at distances up to 7 m. In this paper an inductive link is established between a large planar (1 × 1 m) transmit coil (Tx) and a small planer (170 × 170 mm) receiver coil (Rx), demonstrating the viability of highly asymmetrical coil configurations that real-world applications such as sensor networks impose. High Q factor Tx and Rx coils required for viable power transfer efficiencies over such distances are measured using a resonant method. The applicability of the Class-E amplifier in very low magnetic coupling scenarios and at the high frequencies of operation required for high Q operation is demonstrated by its usage as the Tx coil driver.
  • Conference paper
    Müller MA, Angeli D, Allgöwer F, 2014,

    Performance analysis of economic MPC with self-tuning terminal cost

    , Pages: 2845-2850, ISSN: 0743-1619

    In this paper, we further analyze an economic model predictive control (MPC) algorithm with self-tuning terminal cost, which was recently proposed in [1]. It is shown that if a generalized terminal region constraint instead of a generalized terminal equality constraint is used, improved closed-loop asymptotic average performance bounds can be obtained. In particular, in contrast to the results in [1], these bounds can be obtained a priori. We discuss how the necessary parameters for the generalized terminal region setting can be calculated, and we illustrate our findings with a numerical example. © 2014 American Automatic Control Council.
  • Journal article
    Dzafic I, Pal BC, Gilles M, Henselmeyer S, Sultanic Set al., 2014,

    Generalized π Fortescue Equivalent Admittance Matrix Approach to Power Flow Solution

    , IEEE Transactions on Power Systems, Vol: 29, Pages: 193-202, ISSN: 0885-8950

    This paper develops a generalized admittance matrix approach in Fortescue coordinate system to solve unbalanced/unsymmetrical distribution networks including different number of phases. This generalized Fortescue $pi$ equivalent is defined in this paper for solving the heterogeneous phase, and thus Fortescue, network model. The performance of the approach is demonstrated in different model networks with number of nodes ranging between 168 and 14200. It is found that the current iteration method exploiting the decoupling in admittance matrix in Fortescue coordinate is substantially faster than the typical unbalanced three-phase solution in phase domain. The method has a significant potential for application in real time active power network management.
  • Journal article
    Agalgaonkar YP, Pal BC, Jabr RA, 2014,

    Distribution voltage control considering the impact of PV generation on tap changers and autonomous regulators

    , IEEE Transactions on Power Systems, Vol: 29, Pages: 182-192, ISSN: 0885-8950

    The uptake of variable megawatts from photovoltaics (PV) challenges distribution system operation. The primary problem is significant voltage rise in the feeder that forces existing voltage control devices such as on-load tap-changers and line voltage regulators to operate continuously. The consequence is the deterioration of the operating life of the voltage control mechanism. Also, conventional non-coordinated reactive power control can result in the operation of the line regulator at its control limit (runaway condition). This paper proposes an optimal reactive power coordination strategy based on the load and irradiance forecast. The objective is to minimize the number of tap operations so as not to reduce the operating life of the tap control mechanism and avoid runaway. The proposed objective is achieved by coordinating various reactive power control options in the distribution network while satisfying constraints such as maximum power point tracking of PV and voltage limits of the feeder. The option of voltage support from PV plant is also considered. The problem is formulated as constrained optimization and solved through the interior point technique. The effectiveness of the approach is demonstrated in a realistic distribution network model.
  • Journal article
    Angeli D, Banaji M, Pantea C, 2014,

    COMBINATORIAL APPROACHES TO HOPF BIFURCATIONS IN SYSTEMS OF INTERACTING ELEMENTS

    , COMMUNICATIONS IN MATHEMATICAL SCIENCES, Vol: 12, Pages: 1101-1133, ISSN: 1539-6746
  • Conference paper
    Shabbir W, Evangelou SA, 2014,

    Efficiency analysis of a continuously variable transmission with linear control for a series hybrid electric vehicle

    , 19th World Congress of the International-Federation-of-Automatic-Control (IFAC), Publisher: ELSEVIER SCIENCE BV, Pages: 6264-6269, ISSN: 2405-8963
  • Conference paper
    Arana C, Evangelou SA, Dini D, 2014,

    Car attitude control by series mechatronic suspension

    , 19th World Congress of the International-Federation-of-Automatic-Control (IFAC), Publisher: ELSEVIER SCIENCE BV, Pages: 10688-10693, ISSN: 2405-8963
  • Conference paper
    Scarciotti G, Astollfi A, 2014,

    Model Reduction by Moment Matching for Linear Time-Delay Systems

    , 19th World Congress of the International-Federation-of-Automatic-Control (IFAC), Publisher: ELSEVIER SCIENCE BV, Pages: 9462-9467, ISSN: 2405-8963
  • Conference paper
    Teng F, Pudjianto D, Strbac G, Ferretti F, Bove Ret al., 2014,

    Assessment of the value of plant flexibility in low carbon energy system

    This paper examines the value of flexibility from thermal power plant in the future low carbon energy system. Stochastic scheduling model with rolling planning is performed to calculate the operation cost saving due to improved flexibility. The model optimally schedule energy and ancillary services by explicitly modelling of uncertainties associated with renewable production and generation outage. Various flexibility features are defined and analysed across two representative systems showing that the value of plant flexibility is system specific. Sensitivity studies are carried out to understand the impact of different scheduling methods and carbon taxes on the value of flexibility. This paper also presents the discussion on market reward for flexibility.
  • Conference paper
    Schiffer J, Ortega R, Astolfi A, Raisch J, Sezi Tet al., 2014,

    Stability of Synchronized Motions of Inverter-Based Microgrids Under Droop Control

    , 19th World Congress of the International-Federation-of-Automatic-Control (IFAC), Publisher: ELSEVIER SCIENCE BV, Pages: 6361-6367, ISSN: 2405-8963
  • Conference paper
    Nunna K, Toh TT, Mitcheson PD, Astolfi Aet al., 2014,

    Nonlinear observer and controller design for sensorless operation of a continuously rotating energy harvester

    , 19th World Congress of the International-Federation-of-Automatic-Control (IFAC), Publisher: ELSEVIER SCIENCE BV, Pages: 55-60, ISSN: 2405-8963

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