Results
- Showing results for:
- Reset all filters
Search results
-
Conference paperPadoan A, Astolfi A, 2015,
Dimension estimation for autonomous nonlinear systems
, 54th IEEE Conference on Decision and Control, Publisher: IEEE, Pages: 103-108The problem of estimating the dimension of the state-space of an autonomous nonlinear system is considered. Assuming that sampled measurements of the output and finitely many of its time derivatives are available, an exhaustive search algorithm able to retrieve the dimension of the minimal state-space realization is proposed. The performance of the algorithm are evaluated on specific nonlinear systems.
-
Journal articleJiang J, Astolfi A, 2015,
State and output-feedback shared-control for a class of linear constrained systems
, IEEE Transactions on Automatic Control, Vol: 61, Pages: 3209-3214, ISSN: 0018-9286This paper presents state and output feedback sharedcontrol algorithms for a class of linear systems in the presence of constraints on the output described by means of linear inequalities. The properties of the closed-loop shared-control systems are studied using Lyapunov arguments. Simulation results demonstrate the effectiveness of the algorithm.
-
Journal articleYin J, Lin D, Parisini T, et al., 2015,
Front-End Monitoring of the Mutual Inductance and Load Resistance in a Series-Series Compensated Wireless Power Transfer System
, IEEE Transactions on Power Electronics, Vol: 31, Pages: 7339-7352, ISSN: 1941-0107In this paper, a new method to estimate the mutual inductance and load resistance in a series-series compensated wireless power transfer system is presented. Reasonably accurate estimations can be obtained from measurements of the input voltage and current obtained at one operating frequency only. The proposal can be used to dynamically monitor both the coupling relationship between the transmitter and receiver coils and the load conditions without any direct measurement on the receiver side. It can also be used as a simple method to measure the mutual inductance of any pair of coupled coils. A novel impedance spectrum analysis method is further presented to show that series-series compensation has special characteristics in its input impedance spectrum. Experimental results with acceptable tolerance are included to show the effectiveness of the proposed method.
-
Conference paperPalma V, Suardi A, Kerrigan EC, 2015,
Sensitivity-based multistep MPC for embedded systems
, 5th IFAC Conference on Nonlinear Model Predictive Control 2015 (NMPC'15), Publisher: Elsevier, Pages: 360-365, ISSN: 1474-6670In model predictive control (MPC), an optimization problem is solved every sampling instant to determine an optimal control for a physical system. We aim to accelerate this procedure for fast systems applications and address the challenge of implementing the resulting MPC scheme on an embedded system with limited computing power. We present the sensitivity-based multistep MPC, a strategy which considerably reduces the computing requirements in terms of floating point operations (FLOPs), compared to a standard MPC formulation, while fulfilling closed- loop performance expectations. We illustrate by applying the method to a DC-DC converter model and show how a designer can optimally trade off closed-loop performance considerations with computing requirements in order to fit the controller into a resource-constrained embedded system.
-
Conference paperKerrigan EC, 2015,
Feedback and time are essential for the optimal control of computing systems
, 5th IFAC Conference on Nonlinear Model Predictive Control, Publisher: Elsevier, Pages: 380-387, ISSN: 1474-6670The performance, reliability, cost, size and energy usage of computing systems can be improved by one or more orders of magnitude by the systematic use of modern control and optimization methods. Computing systems rely on the use of feedback algorithms to schedule tasks, data and resources, but the models that are used to design these algorithms are validated using open-loop metrics. By using closed-loop metrics instead, such as the gap metric developed in the control community, it should be possible to develop improved scheduling algorithms and computing systems that have not been over-engineered. Furthermore, scheduling problems are most naturally formulated as constraint satisfaction or mathematical optimization problems, but these are seldom implemented using state of the art numerical methods, nor do they explicitly take into account the fact that the scheduling problem itself takes time to solve. This paper makes the case that recent results in real-time model predictive control, where optimization problems are solved in order to control a process that evolves in time, are likely to form the basis of scheduling algorithms of the future. We therefore outline some of the research problems and opportunities that could arise by explicitly considering feedback and time when designing optimal scheduling algorithms for computing systems.
-
Conference paperBoem 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: 0743-1546This 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 paperBoem 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: 0743-1546The 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 paperScarciotti 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 paperScarciotti 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 articleManfredi S, Angeli D, 2015,
Frozen state conditions for exponential consensus of time-varying cooperative nonlinear networks
, Automatica, Vol: 64, Pages: 182-189, ISSN: 1873-2836In 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 articleAngeli 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: 0018-9286We 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 articleSegundo Sevilla FR, Jaimoukha I, Chaudhuri B, et al., 2015,
A semidefinite relaxation procedure for fault-tolerant observer design
, IEEE Transactions on Automatic Control, Vol: 60, Pages: 3332-3337, ISSN: 0018-9286A 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 articleChen 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- Author Web Link
- Cite
- Citations: 36
-
Conference paperJiang J, Astolfi A, 2015,
Shared-Control for a UAV Operating in the 3D Space
, European Control Conference 2015, Publisher: IEEEThis 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 paperSuardi A, Kerrigan EC, Constantinides GA, 2015,
Fast FPGA prototyping toolbox for embedded optimization
, European Control Conference (ECC), Publisher: IEEE, Pages: 2589-2594Traditionally 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 articleIonescu TC, Astolfi A, 2015,
Nonlinear moment matching-based model order reduction
, IEEE Transactions on Automatic Control, Vol: 61, Pages: 2837-2847, ISSN: 0018-9286In 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 articleVinter RB, 2015,
Multifunctions of bounded variation
, Journal of Differential Equations, Vol: 260, Pages: 3350-3379, ISSN: 1090-2732Consider 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 paperManfredi S, Angeli D, 2015,
On exponential consensus for time-varying non-cooperative nonlinear networks
, ECC 2015, Publisher: IEEE, Pages: 557-562In 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 paperScarciotti 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: 334-339An 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 articleHo GKY, Zhang C, Pong BMH, et al., 2015,
Modeling and Analysis of the Bendable Transformer
, IEEE Transactions on Power Electronics, Vol: 31, Pages: 6450-6460, ISSN: 0885-8993This 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 articleBachtiar V, Kerrigan EC, Moase WH, et 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: 1873-2836The 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 articleZhao Z, Yang P, Cai Z, et 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: 1006-6047The 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 articleMayne D, Falugi P, 2015,
Generalised stabilizing conditions for model predictive control
, Journal of Optimization Theory and Applications, Vol: 169, Pages: 719-734, ISSN: 1573-2878This 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 articleZhao Z, Yang P, Guerrero JM, et 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 articleChen HT, Cheung YF, Choi HW, et 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- Author Web Link
- Cite
- Citations: 10
-
Journal articleBarocio E, Pal BC, Thornhill NF, et 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- Author Web Link
- Cite
- Citations: 113
-
Conference paperFerrari 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: 1474-6670This 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 paperChaffey 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: 2329-3721Circuit 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 articleAkhtar 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: 1949-3061This 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 paperSheridan 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 2015It 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.
This data is extracted from the Web of Science and reproduced under a licence from Thomson Reuters. You may not copy or re-distribute this data in whole or in part without the written consent of the Science business of Thomson Reuters.