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  • Conference paper
    Boem F, Parisini T, 2015,

    Distributed model-based fault diagnosis with stochastic uncertainties

    , 2015 54th IEEE Conference on Decision and Control (CDC), Publisher: IEEE, Pages: 4474-4479, ISSN: 0743-1546

    This paper proposes a novel distributed fault detection and isolation approach for the monitoring of non linear large-scale systems. The proposed architecture considers stochastic characterization of the measurement noises and modeling uncertainties, computing at each step stochastic time-varying thresholds with guaranteed false alarms probability levels. The convergence properties of the distributed estimation are demonstrated. A novel fault isolation method is proposed basing on a Generalized Observer Scheme, providing guaranteed error probabilities of the fault exclusion task. A consensus approach is used for the estimation of variables shared among more than one subsystem; a method is proposed to define the time-varying consensus weights in order to minimize at each step the variance of the uncertainty of the fault detection and isolation thresholds. Detectability and isolability conditions are provided.
  • Conference paper
    Boem F, Sabattini L, Secchi C, 2015,

    Decentralized state estimation for heterogeneous multi-agent systems

    , 2015 54th IEEE Conference on Decision and Control (CDC), Publisher: IEEE, Pages: 4121-4126, ISSN: 0743-1546

    The paper proposes a decentralized state estimation method for the control of multi-agent networked systems, where the goal is the tracking of arbitrary setpoint functions. The cooperative agents are partitioned into independent robots, providing the control inputs, and dependent robots, controlled by local interaction laws. The proposed state estimation algorithm allows the independent robots to estimate the state of the dependent robots in a completely decentralized way. To do that, it is necessary for each independent robot to estimate the control input components computed by the other independent robots, without requiring communication among the independent robots. The decentralized state estimator, including an input estimator, is developed and the convergence properties are studied. Simulation results show the effectiveness of the proposed approach.
  • Conference paper
    Scarciotti G, 2015,

    Model reduction by moment matching for linear singular systems

    , 2015 54th IEEE Conference on Decision and Control (CDC), Pages: 7310-7315, ISSN: 0743-1546
  • Conference paper
    Scarciotti G, Astolfi A, 2015,

    Model reduction for nonlinear systems and nonlinear time-delay systems from input/output data

    , 2015 54th IEEE Conference on Decision and Control (CDC), Publisher: IEEE, Pages: 7298-7303, ISSN: 0743-1546
  • Journal article
    Manfredi S, Angeli D, 2015,

    Frozen state conditions for exponential consensus of time-varying cooperative nonlinear networks

    , Automatica, Vol: 64, Pages: 182-189, ISSN: 1873-2836

    In this paper we present new results on exponential consensus for continuous-time nonlinear time varying cooperative networks. We endow the well known assumption of integral connectivity proposed by Moreau with a remarkable additional feature of being frozen in state variables, making its direct verification more straightforward. Moreover, we give an estimate of the exponential rate of convergence towards the agreement space. Finally, the proposed results are validated for representative examples.
  • Journal article
    Angeli D, Efimov D, 2015,

    Characterizations of Input-to-State Stability for systems with multiple invariant sets

    , IEEE Transactions on Automatic Control, Vol: 60, Pages: 3242-3256, ISSN: 0018-9286

    We generalize the theory of Input-to-State Stability (ISS) and of its characterizations by means of Lyapunov dissipation inequalities to the study of systems admitting invariant sets, which are not necessarily stable in the sense of Lyapunov but admit a suitable hierarchical decomposition. It is the latter which allows to greatly extend the class of systems to which ISS theory can be applied, allowing in a unified treatment to deal with oscillators in Euclidean coordinates, almost globally asymptotically stable systems on manifolds, systems with multiple equilibria in Rn just to name a few.
  • Journal article
    Segundo Sevilla FR, Jaimoukha I, Chaudhuri B, Korba Pet al., 2015,

    A semidefinite relaxation procedure for fault-tolerant observer design

    , IEEE Transactions on Automatic Control, Vol: 60, Pages: 3332-3337, ISSN: 0018-9286

    A fault-tolerant observer design methodology is proposed. The aim is to guarantee a minimum level of closed-loop performance under all possible sensor fault combinations while optimizing performance under the nominal, fault-free condition. A novel approach is proposed to tackle the combinatorial nature of the problem, which is computationally intractable even for a moderate number of sensors, by recasting the problem as a robust performance problem, where the uncertainty set is composed of all combinations of a set of binary variables. A procedure based on an elimination lemma and an extension of a semidefinite relaxation procedure for binary variables is then used to derive sufficient conditions (necessary and sufficient in the case of one binary variable) for the solution of the problem which significantly reduces the number of matrix inequalities needed to solve the problem. The procedure is illustrated by considering a fault-tolerant observer switching scheme in which the observer outputs track the actual sensor fault condition. A numerical example from an electric power application is presented to illustrate the effectiveness of the design.
  • Journal article
    Chen H-T, Tan S-C, Hui SYR, 2015,

    Nonlinear Dimming and Correlated Color Temperature Control of Bicolor White LED Systems

    , IEEE TRANSACTIONS ON POWER ELECTRONICS, Vol: 30, Pages: 6934-6947, ISSN: 0885-8993
  • Conference paper
    Jiang J, Astolfi A, 2015,

    Shared-Control for a UAV Operating in the 3D Space

    , European Control Conference 2015, Publisher: IEEE

    This paper presents a shared-control scheme for a UAV moving in a 3D space while its feasible Cartesian position set is defined by a group of linear inequalities. A hysteresis switch is used to combine the human input and the feedback control input based on the definitions of a safe set, a hysteresis set and a “dangerous” set. Case studies given in the paper show the effectiveness of the shared-control algorithm.
  • Conference paper
    Suardi A, Kerrigan EC, Constantinides GA, 2015,

    Fast FPGA prototyping toolbox for embedded optimization

    , European Control Conference (ECC), Publisher: IEEE, Pages: 2589-2594

    Traditionally compute-intensive optimisation algorithms have been implemented on CPU based machines, primarily in order to reduce development time, but sacrificing computing speed and energy consumption. However, recent advancements in FPGA technologies are making the design effort comparable to that of CPUs, making them an increasingly viable option. This paper presents FPGA IP prototyping toolbox (PROTOIP), which is an Open Source framework conceived to enable researchers and engineers to design, validate and prototype algorithms quickly on FPGA platforms. Abstracting many low-level FPGA design details, PROTOIP provides custom templates, scripts, example designs and tutorials specifically tailored for embedded optimization applications.
  • Journal article
    Ionescu TC, Astolfi A, 2015,

    Nonlinear moment matching-based model order reduction

    , IEEE Transactions on Automatic Control, Vol: 61, Pages: 2837-2847, ISSN: 0018-9286

    In this paper we present a time-domain notion of moments for a class of single-input, single-output nonlinear systems in terms of the evolution of the output of a generalized signal generator driven by the nonlinear system. We also define a new notion of moment matching and present a family of (nonlinear) parametrized reduced order models that achieve moment matching. We establish relations with existing notions of moment for nonlinear systems, showing that the newly derived and the existing families of reduced order models that achieve nonlinear moment matching, respectively, are equivalent. Furthermore, we compute the reduced order model that matches the moments at two chosen signal generators (one exciting the input of the system and another driven by the system), simultaneously. We also present a family of models computed on the basis of a nonlinear extension of the Petrov-Galerkin projection that achieve moment matching. Finally, we specialize the results to the case of nonlinear, input-affine systems.
  • Journal article
    Vinter RB, 2015,

    Multifunctions of bounded variation

    , Journal of Differential Equations, Vol: 260, Pages: 3350-3379, ISSN: 1090-2732

    Consider control systems described by a differential equation with a control term or, more generally, by a differential inclusion with velocity set F(t,x). Certain properties of state trajectories can be derived when it is assumed that F(t,x) is merely measurable w.r.t. the time variable t . But sometimes a refined analysis requires the imposition of stronger hypotheses regarding the time dependence. Stronger forms of necessary conditions for minimizing state trajectories can be derived, for example, when F(t,x) is Lipschitz continuous w.r.t. time. It has recently become apparent that significant addition properties of state trajectories can still be derived, when the Lipschitz continuity hypothesis is replaced by the weaker requirement that F(t,x) has bounded variation w.r.t. time. This paper introduces a new concept of multifunctions F(t,x) that have bounded variation w.r.t. time near a given state trajectory, of special relevance to control. We provide an application to sensitivity analysis.
  • Conference paper
    Manfredi S, Angeli D, 2015,

    On exponential consensus for time-varying non-cooperative nonlinear networks

    , ECC 2015, Publisher: IEEE, Pages: 557-562

    In this paper we present new results on asymptotic consensus for continuous-time nonlinear time varying networks. A key feature in the following is that the monotonicity property (i.e. cooperativity) is not required, unlike most of existing literature on the subject. Additionally, we extend the use of a 'State Frozen' concept [16] and integral connectivity to this non-trivial scenario, and give condition for consensus with the additional merit to be frozen in state variables and therefore of simpler verification. Finally, we give an estimate of the exponential rate of convergence towards the agreement manifold.
  • Conference paper
    Scarciotti G, Astolfi A, 2015,

    Model reduction for linear systems and linear time-delay systems from input/output data

    , 2015 European Control Conference (ECC), Publisher: IEEE, Pages: 334-339

    An algorithm for the estimation of the moments of linear systems and linear time-delay systems from input/output data is proposed. The estimate, which converges to the moments of the system, is exploited to construct a family of reduced order models. These models asymptotically match the moments of the unknown system to be reduced. The computational complexity of the algorithm is analyzed and the use of the algorithm is illustrated by a benchmark example.
  • Journal article
    Ho GKY, Zhang C, Pong BMH, Hui SYRet al., 2015,

    Modeling and Analysis of the Bendable Transformer

    , IEEE Transactions on Power Electronics, Vol: 31, Pages: 6450-6460, ISSN: 0885-8993

    This paper presents a study of a bendable transformer for wearable electronics. Printed on a thin and bendable film, this transformer is bendable to wrap around body limbs such as the forearm. A model using a partial equivalent circuit theory has been developed to analyze the characteristic of an inductor and a bendable transformer. The mutual inductance and self-inductance for the bendable transformer over a range of bent curvatures have been calculated based on the model and compared favorably with measurements. Simulation and experimental results of applying the bendable inductor and transformer in dc-dc converters as a 5-V 500-mA power supply are included to confirm the usefulness of the transformer and the validity of the model.
  • Journal article
    Bachtiar V, Kerrigan EC, Moase WH, Manzie Cet al., 2015,

    Continuity and Monotonicity of the MPC Value Function with respect to Sampling Time and Prediction Horizon

    , Automatica, Vol: 63, Pages: 330-337, ISSN: 1873-2836

    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
    Zhao Z, Yang P, Cai Z, Zhou S, Green TC, Lei Jet al., 2015,

    Analysis and improvement of steady-state voltage stability for isolated medium-voltage microgrid with wind power

    , Dianli Zidonghua Shebei/Electric Power Automation Equipment, Vol: 35, Pages: 13-19, ISSN: 1006-6047

    The power-voltage characteristics of DFIG (Doubly-Fed Induction Generator) with wind turbine in the isolated microgrid are analyzed and a strategy based on the local energy-storage stability control and fast pitch-angle control is proposed according to the constraints of different operating modes of microgrid with DFIG to enhance its steady-state voltage stability control. A model of microgrid system with stability control strategy is built based on PSCAD /EMTDC and the results of research indicate that, the proposed strategy enhances effectively the steady-state voltage stability of microgrid under the wind disturbances in different operating modes to guarantee its safe and stable operation.
  • Journal article
    Mayne D, Falugi P, 2015,

    Generalised stabilizing conditions for model predictive control

    , Journal of Optimization Theory and Applications, Vol: 169, Pages: 719-734, ISSN: 1573-2878

    This note addresses the tracking problem for model predictive control. It presents simple procedures for both linear and nonlinear constrained model predictive control when the desired equilibrium state is any point in a specified set. The resultant region of attraction is the union of the regions of attraction for each equilibrium state in the specified set and is therefore larger than that obtained when conventional model predictive control is employed.
  • Journal article
    Zhao Z, Yang P, Guerrero JM, Xu Z, Green TCet al., 2015,

    Multiple-time-scales hierarchical frequency stability control strategy of medium-voltage isolated microgrid

    , IEEE Transactions on Power Electronics, Vol: 31, Pages: 5974-5991, ISSN: 1941-0107
  • Journal article
    Chen HT, Cheung YF, Choi HW, Tan SC, Hui SYet al., 2015,

    Reduction of Thermal Resistance and Optical Power Loss Using Thin-Film Light-Emitting Diode (LED) Structure

    , IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, Vol: 62, Pages: 6925-6933, ISSN: 0278-0046
  • Journal article
    Barocio E, Pal BC, Thornhill NF, Roman Messina Aet al., 2015,

    A Dynamic Mode Decomposition Framework for Global Power System Oscillation Analysis

    , IEEE TRANSACTIONS ON POWER SYSTEMS, Vol: 30, Pages: 2902-2912, ISSN: 0885-8950
  • Conference paper
    Ferrari RMG, Boem F, Parisini T, 2015,

    An algebraic approach to modeling distributed multiphysics problems: The case of a DRI reactor

    , 4th IFAC Workshop on Mining, Mineral and Metal Processing MMM 2015, Publisher: Elsevier, Pages: 155-160, ISSN: 1474-6670

    This paper deals with the problem of modelling a chemical reactor for the Direct Reduction of Iron ore (DRI). Such a process is being increasingly promoted as a more viable alternative to the classic Blast Furnace for the production of iron from raw minerals. Due to the inherent complexity of the process and the reactor itself, its effective monitoring and control requires advanced mathematical models containing distributed-parameter components. While classical approaches such as Finite Element or Finite Differences are still reasonable options, for accuracy and computational efficiency reasons, an algebraic approach is proposed. A full multi-physical, albeit one-dimensional model is addressed and its accuracy is analysed.
  • Conference paper
    Chaffey G, Green TC, 2015,

    Directional current breaking capacity requirements for HVDC circuit breakers

    , 2015 IEEE Energy Conversion Congress and Exposition (ECCE), Publisher: IEEE, Pages: 5371-5377, ISSN: 2329-3721

    Circuit breakers are expected to be a vital element within any high capacity HVDC network. This paper examines the directional current breaking capacity requirements that might be seen on a typical HVDC grid, as required for the specification of backup protection. It is shown that there is a significant difference between the peak prospective fault currents observed when the current direction is analysed. Several meshed network topologies are examined in order to evaluate and quantify the characteristics of the directional breaker requirement. Results are presented determining that both the current breaking magnitude duty and the time constraint typically associated with the DC fault are both significantly different when comparing the current direction through the breaker, which may influence future breaker design.
  • Journal article
    Akhtar Z, Chaudhuri B, Hui S, 2015,

    Smart Loads for Voltage Control in Distribution Networks

    , IEEE Transactions on Smart Grid, Vol: 8, Pages: 937-946, ISSN: 1949-3061

    This paper shows that the smart loads (SLs) couldbe effective in mitigating voltage problems caused by photovoltaic(PV) generation and electric vehicle (EV) chargingin low-voltage (LV) distribution networks. Limitations of thepreviously reported SL configuration with only series reactivecompensator (SLQ) (one converter) is highlighted in this paper.To overcome these limitations, an additional shunt converter isused in back-to-back (B2B) configuration to support the activepower exchanged by the series converter, which increases the flexibilityof the SL without requiring any energy storage. Simulationresults on a typical U.K. LV distribution network are presented tocompare the effectiveness of an SL with B2B converters (SLBCs)against an SLQ in tackling under- and over-voltage problemscaused by EV or PV. It is shown that SLBCs can regulate themain voltage more effectively than SLQs especially under overvoltagecondition. Although two converters are required for eachSLBC, it is shown that the apparent power capacity of eachconverter is required to be significantly less than that of anequivalent SLQ.
  • Conference paper
    Sheridan CE, Merlin MMC, Green TC, 2015,

    Benefits of Operating a Four Terminal HVDC Network with a Normally Open Point

    , International High Voltage Direct Current Conference 2015

    It is likely that any HVDC grids will evolve over time and will likely be multi-vendor and use several different technologies. This paper studies a four terminal network where the interconnecting link is operated as a normally open point. This allows the network to be reconfigured in the event of DC side fault, without the need for DC circuit breakers. The network uses the popular Modular Multi-level converter at one terminal and a fault tolerant converter at the other terminal. A simple cost benefit shows the economic advantage of the interconnecting link. The operation of this network is then verified through simulation for a normal operating scenario and a DC fault scenario.
  • Conference paper
    Pipelzadeh Y, Chaudhuri B, Green T, 2015,

    Modelling and Dynamic Operation of the Zhoushan DC Grid: Worlds First Five-Terminal VSC-HVDC Project

    , International High Voltage Direct Current 2015 Conference, Publisher: IET, Pages: 87-95

    This paper highlights the world’s first operational MTDC grid, namely the 5-terminal Zhoushan DC grid. The scheme went under operation in 2014. The topology and operation of the Zhoushan DC grid are demonstrated with recorded measurements obtained from the converter station, after being subjected to system disturbances. A generic modeling framework for the Zhoushan DC grid is developed inPSCAD/EMTDC. One particular concern is how the Zhoushan DC grid would react to DC side faults and the resulting power imbalance. Despite the completion of the Zhoushan MTDC grid, technological barriers such as the unavailability of fast protection systems, DC circuit breakers and highly efficient VSCs with DC side fault-clearing capabilities have all been bottlenecks at the time of commissioning, but are now under extensive research and development. The challenges and importance of DC grid protection are highlighted through case studies performed on the DC grid model in PSCAD/EMTDC.
  • Journal article
    Teng F, Aunedi M, Strbac G, 2015,

    Benefits of flexibility from smart electrified transportation and heating in the future UK electricity system

    , Applied Energy, Vol: 167, Pages: 420-431, ISSN: 1872-9118

    This paper presents an advanced stochastic analytical framework to quantify the benefits of smart electric vehicles (EVs) and heat pumps (HPs) on the carbon emission and the integration cost of renewable energy sources (RES) in the future UK electricity system. The typical operating patterns of EVs/HPs as well as the potential flexibility to perform demand shifting and frequency response are sourced from recent UK trials. A comprehensive range of case studies across several future UK scenarios suggest that smart EVs/HPs could deliver measurable carbon reductions by enabling a more efficient operation of the electricity system, while at the same time making the integration of electrified transport and heating demand significantly less carbon intensive. The second set of case studies establish that smart EVs/HPs have significant potential to support cost-efficient RES integration by reducing: (a) RES balancing cost, (b) cost of required back-up generation capacity, and (c) cost of additional low-carbon capacity required to offset lower fuel efficiency and curtailed RES output while achieving the same emission target. Frequency response provision from EVs/HPs could significantly enhance both the carbon benefit and the RES integration benefit of smart EVs/HPs.
  • Conference paper
    Boem F, Riverso S, Ferrari-Trecate G, Parisini Tet al., 2015,

    A plug-and-play fault diagnosis approach for large-scale systems

    , 9th IFAC Symposium on Fault Detection, Supervision and Safety for Technical Processes SAFEPROCESS 2015, Publisher: Elsevier, Pages: 601-606, ISSN: 1474-6670

    This paper proposes a novel Plug-and-Play (PnP) dynamic approach for the monitoring of Large-Scale Systems (LSSs). The proposed architecture exploits a distributed Fault Detection and Isolation (FDI) methodology for nonlinear LSS in a PnP framework. The LSS consists of several interconnected subsystems and the designed FDI architecture is able to manage plugging-in of novel subsystems and un-plugging of existing ones. Moreover, the proposed PnP approach performs the unplugging of faulty subsystems in order to avoid the propagation of faults in the interconnected LSS. Analogously, once the issue has been solved, the disconnected subsystem can be re-plugged-in. The reconfiguration processes only involves local operations of neighboring subsystems, thus allowing a distributed architecture.
  • Conference paper
    Boem F, Ferrari RMG, Parisini T, Polycarpou MMet al., 2015,

    Optimal topology for distributed fault detection of large-scale systems

    , 9th IFAC Symposium on Fault Detection, Supervision and Safety for Technical Processes SAFEPROCESS 2015, Publisher: Elsevier, Pages: 60-65, ISSN: 1474-6670

    The paper deals with the problem of defining the optimal topology for a distributed fault detection architecture for non-linear large-scale systems. A stochastic modelbased framework for diagnosis is formulated. The system structural graph is decomposed into subsystems and each subsystem is monitored by one local diagnoser. It is shown that overlapping of subsystems allows to improve the detectability properties of the monitoring architecture. Based on this theoretical result, an optimal decomposition design method is proposed, able to define the minimum number of detection units needed to guarantee the detectability of certain faults while minimizing the communication costs subject to some computation cost constraints. An algorithmic procedure is presented to solve the proposed optimal decomposition problem. Preliminary simulation results show the potential of the proposed approach.
  • Journal article
    Zhao Z, Yang P, Cai Z, Zhou S, Green TCet al., 2015,

    Cooperative control of transient voltage stability for islanded medium-voltage microgrid with wind power

    , Dianli Zidonghua Shebei/Electric Power Automation Equipment, Vol: 35, Pages: 1-9, ISSN: 1006-6047

    The transient operating characteristics of DFIG(Doubly-Fed Induction Generator) and dynamic loads are analyzed for islanded medium-voltage microgrid. A locally coordinative control strategy based on the energy storage stability control, fast wind turbine pitch angle control and dynamic load shedding is proposed to improve the transient voltage stability of microgrid with DFIG. The medium-voltage microgrid system of Dongao Island and the corresponding stability control strategy model are established based on PSCAD/EMTDC. Research results indicate that, the transient voltage stability of microgrid is closely related to the penetration rate of wind power and the load characteristic;the proposed control strategy can effectively enhance the voltage stability of microgrid under serious disturbance.

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