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  • Journal article
    Palladino M, Vinter RB, 2015,

    When are minimizing controls also minimizing relaxed controls?

    , Discrete and Continuous Dynamical Systems, Vol: 35, Pages: 4573-4592, ISSN: 1553-5231

    Relaxation refers to the procedure of enlarging the domain of a variational problem or the search space for the solution of a set of equations, to guarantee the existence of solutions. In optimal control theory relaxation involves replacing the set of permissible velocities in the dynamic constraint by its convex hull. Usually the infimum cost is the same for the original optimal control problem and its relaxation. But it is possible that the relaxed infimum cost is strictly less than the infimum cost. It is important to identify such situations, because then we can no longer study the infimum cost by solving the relaxed problem and evaluating the cost of the relaxed minimizer. Following on from earlier work by Warga, we explore the relation between the existence of an infimum gap and abnormality of necessary conditions (i.e. they are valid with the cost multiplier set to zero). Two kinds of theorems are proved. One asserts that a local minimizer, which is not also a relaxed minimizer, satisfies an abnormal form of the Pontryagin Maximum Principle. The other asserts that a local relaxed minimizer that is not also a minimizer satisfies an abnormal form of the relaxed Pontryagin Maximum Principle.
  • Journal article
    Jones BL, Heins PH, Kerrigan EC, Morrison JF, Sharma ASet al., 2015,

    Modelling for robust feedback control of fluid flows

    , Journal of Fluid Mechanics, Vol: 769, Pages: 687-722, ISSN: 0022-1120

    This paper addresses the problem of designing low-order and linear robust feedback controllers that provide a priori guarantees with respect to stability and performance when applied to a fluid flow. This is challenging, since whilst many flows are governed by a set of nonlinear, partial differential–algebraic equations (the Navier–Stokes equations), the majority of established control system design assumes models of much greater simplicity, in that they are: firstly, linear; secondly, described by ordinary differential equations (ODEs); and thirdly, finite-dimensional. With this in mind, we present a set of techniques that enables the disparity between such models and the underlying flow system to be quantified in a fashion that informs the subsequent design of feedback flow controllers, specifically those based on the H∞ loop-shaping approach. Highlights include the application of a model refinement technique as a means of obtaining low-order models with an associated bound that quantifies the closed-loop degradation incurred by using such finite-dimensional approximations of the underlying flow. In addition, we demonstrate how the influence of the nonlinearity of the flow can be attenuated by a linear feedback controller that employs high loop gain over a select frequency range, and offer an explanation for this in terms of Landahl’s theory of sheared turbulence. To illustrate the application of these techniques, an H∞ loop-shaping controller is designed and applied to the problem of reducing perturbation wall shear stress in plane channel flow. Direct numerical simulation (DNS) results demonstrate robust attenuation of the perturbation shear stresses across a wide range of Reynolds numbers with a single linear controller.
  • Journal article
    Yin J, Lin D, Lee CK, Parisini T, Hui SYRet al., 2015,

    Front-End Monitoring of Multiple Loads in Wireless Power Transfer Systems Without Wireless Communication Systems

    , IEEE Transactions on Power Electronics, Vol: 31, Pages: 2510-2517, ISSN: 0885-8993

    This paper describes a method for monitoring multiple loads from the front end of a wireless power transfer system without using any wireless communication systems. A mathematical approach based on scanning the frequency around the resonant frequency has been developed for deriving the load conditions. The proposal requires only information of the input voltage and current, thereby eliminating the requirements of using wireless communication systems for feedback control. The proposal has been practically confirmed in hardware prototype with good results.
  • Journal article
    Mok KT, Tan SC, Hui SYR, 2015,

    Decoupled Power Angle and Voltage Control of Electric Springs

    , IEEE Transactions on Power Electronics, Vol: 31, Pages: 1216-1229, ISSN: 1941-0107

    In this paper, a radial-chordal decomposition (RCD) technique is proposed to decouple the power angle and voltage control of a smart load based on the use of electric springs (ES). This RCD method is mathematically presented. A detailed comparison between the existing ES control schemes and the proposed RCD approach highlights its decoupling feature and merit on achieving multiple functionalities with a single ES. This RCD control method has been tested on a 2-kW small-scale power system. Simulation and experimental results confirmed that the power factor of the ES-integrated smart load can be improved by the chordal control while the mains voltage can be regulated by the radial control. It has also been demonstrated that the radial and chordal control can work simultaneously and independently.
  • Conference paper
    Das HB, Evangelou SA, Jabez Dhinagar S, 2015,

    An Objective Evaluation of Characterisation Matrix for Two Wheeler Powertrain with Control Oriented Mathematical Model

    , SAE 2015 World Congress & Exhibition, Publisher: SAE International

    The objective of this paper is to estimate characteristics parameters of two wheeler powertrain with simulated vehicle model. The evaluation is applied to define required characteristics for future motor integrated powertrain. The main parameters for the characteristics matrix are Fuel consumption and NOx gas emission. In the 1st phase of work, a mathematical model for the complete powertrain is developed using suitable modelling approach for different sub-modules of the complete system. The objectives of the model are, to simulate dynamic power-flow from the engine to wheel and to simulate NOx gas emission. The powertrain model consists of a carburetted spark ignition (S.I) engine and gear transmission system. The S.I engine model is capable of simulating dynamic torque output of engine as well as the NOx gas emission. The model is experimentally compared with available test data of production ready engine from TVS Motor Company, India. The dynamic effects of change of ignition timing and fueling on torque output and NOx gas emissions are simulated based on this model and discussed on the paper. The paper adapted two types of transmission model, one with Continuous Variable Transmission (CVT) and other one with Fixed Geared Transmission. The mathematical model for the CVT system is developed to capture automatic gear shift actuation and power transfer to the wheel. The model simulates the toque control system of the driven pulley as well as speed control system of the drive pulley. The mathematical model for the fixed gear ratio system with wet clutch system is proposed to simulate the manual gear based powertrain. The above mentioned model demands computationally intensive resources due to presence of higher order dynamics, mathematical discontinuity and non-linear functions. So this model is not suitable for control design application. In 2nd phase of work, the model is converted to lower complexity control oriented model by using feed-forward approach. The contr
  • Conference paper
    Meisel J, Shabbir W, Evangelou SA, 2015,

    Control of PHEV and HEV Parallel Powertrains Using a Sequential Linearization Algorithm

    Using measurable physical input variables, an implementable control algorithm for parallel architecture plug-in and non-plug-in hybrid electric vehicle (PHEV and HEV) powertrains is presented. The control of the electric drive is based on an algebraic mapping of the accelerator pedal position, the battery state-of-charge (SOC), and the vehicle velocity into a motor controller input torque command. This mapping is developed using a sequential linearization control (SLC) methodology. The internal combustion engine (ICE) control uses a modified accelerator pedal to throttle plate angle using an adjustable gain parameter that, in turn, determines the sustained battery SOC. Searches over an admissible control space or the use of pre-defined look-up tables are thus avoided. Actual on-road results for a Ford Explorer with a through-the-road (TTR) hybrid powertrain using this control methodology are presented. In addition, Matlab-based simulation results for PHEVs and HEVs using this single control algorithm are presented employing a model of the Explorer. These results show the gasoline consumption and SOC over 48 repeated cycles of three common driving schedules. Further studies of acceleration performance illustrate the trade-off of minimizing gasoline consumption vs. higher performance using more gasoline. All-electric range (AER) vs. battery capacity is also presented as well as the fuel consumption and final SOC for two PHEV control strategies.
  • Journal article
    Teng F, Pudjianto D, Strbac G, Brandon N, Thomson A, Miles Jet al., 2015,

    Potential value of energy storage in the UK electricity system

    , Proceedings of the ICE - Energy, Vol: 168, Pages: 107-117, ISSN: 1751-4223

    This paper assesses the value of distributed energy storage and informs the business case for its multiple applications in the UK electricity system. In contrast to earlier studies that focus on the benefits of energy storage for system operation and development, this work analyses the value that it may deliver to the owner. For this purpose, three models are proposed and applied to analyse the benefit of energy storage with applications in energy and ancillary service markets, revenue maximisation in the context of feed-in tariffs and reduction of carbon dioxide emissions. A large set of studies is carried out to quantify the commercial and emissions benefits of energy storage for those applications. Sensitivity analysis across various scenarios is performed to understand the key drivers for the value of energy storage and how it is affected by energy storage parameters and other factors such as network constraints, prices of energy and ancillary services, and inherent energy system characteristics. A review of current and near-term storage technology costs and functionality is also presented.
  • Journal article
    Mylvaganam T, Sassano M, Astolfi A, 2015,

    Constructive epsilon-nash equilibria for nonzero-sum differential games

    , IEEE Transactions on Automatic Control, Vol: 60, Pages: 950-965, ISSN: 0018-9286

    In this paper, a class of infinite-horizon, nonzero-sum differential games and their Nash equilibria are studied and the notion of ε α -Nash equilibrium strategies is introduced. Dynamic strategies satisfying partial differential inequalities in place of the Hamilton-Jacobi-Isaacs partial differential equations associated with the differential games are constructed. These strategies constitute (local) ε α -Nash equilibrium strategies for the differential game. The proposed methods are illustrated on a differential game for which the Nash equilibrium strategies are known and on a Lotka-Volterra model, with two competing species. Simulations indicate that both dynamic strategies yield better performance than the strategies resulting from the solution of the linear-quadratic approximation of the problem.
  • Conference paper
    Bachtiar V, Kerrigan EC, Moase WH, Manzie Cet al., 2015,

    Smoothness Properties of the MPC Value Function with respect to Sampling Time and Prediction Horizon

    , 10th Asian Control Conference (ASCC)
  • Journal article
    Feldman J, Hanrahan BM, Misra S, Fan XZ, Waits CM, Mitcheson PD, Ghodssi Ret al., 2015,

    Vibration-Based Diagnostics for Rotary MEMS

    , JOURNAL OF MICROELECTROMECHANICAL SYSTEMS, Vol: 24, Pages: 289-299, ISSN: 1057-7157
  • Journal article
    Bowden JA, Burrow SG, Cammarano A, Clare LR, Mitcheson PDet al., 2015,

    Switched-Mode Load Impedance Synthesis to Parametrically Tune Electromagnetic Vibration Energy Harvesters

    , IEEE-ASME TRANSACTIONS ON MECHATRONICS, Vol: 20, Pages: 603-610, ISSN: 1083-4435
  • Journal article
    Liu Y, Van Schijndel J, Longo S, Kerrigan ECet al., 2015,

    UAV Energy Extraction With Incomplete Atmospheric Data Using MPC

    , IEEE TRANSACTIONS ON AEROSPACE AND ELECTRONIC SYSTEMS, Vol: 51, Pages: 1203-1215, ISSN: 0018-9251
  • Conference paper
    Zhang X, Green TC, 2015,

    The new family of high step ratio modular multilevel DC-DC converters

    , 2015 IEEE Applied Power Electronics Conference and Exposition (APEC), Publisher: IEEE, Pages: 1743-1750

    This paper presents a family of modular multilevel converters (MMCs) for high step ratio dc-dc conversion. The modular multilevel unidirectional step-down dc-dc converter topologies are presented. The high step-up ratio bidirectional modular multilevel dc-dc converter is also provided. Operation principle and analysis of the bidirectional dc-dc converter are shown, and verified by experimental results with a conversion ratio of 1 : 10. The proposed converters achieve high voltage step ratio depending on the number of sub-modules and the charging ratio.
  • Journal article
    Welsch M, Howells M, Hesamzadeh MR, Gallachoir BO, Deane P, Strachan N, Bazilian M, Kammen DM, Jones L, Strbac G, Rogner Het al., 2015,

    Supporting security and adequacy in future energy systems: The need to enhance long-term energy system models to better treat issues related to variability

    , INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Vol: 39, Pages: 377-396, ISSN: 0363-907X
  • Journal article
    De Paola A, Angeli D, Strbac G, 2015,

    Distributed Control of Micro-Storage Devices With Mean Field Games

    , IEEE Transactions on Smart Grid, Vol: 7, Pages: 1119-1127, ISSN: 1949-3061

    This paper proposes a fully distributed control strategyfor the management of micro-storage devices that performenergy arbitrage. For large storage populations the problem canbe approximated as a differential game with infinite players(Mean Field Game). Through the resolution of coupled partialdifferential equations (PDEs), it is possible to determine, as afixed point, the optimal feedback strategy for each player andthe resulting price of energy if that strategy is applied. Oncethis price is calculated, it can be communicated to the deviceswhich are able to independently determine their optimal chargeprofile. Simulation results are provided, calculating the fixedpoint through numerical integration of the PDEs. The originalmodel is then extended in order to consider additional elementssuch as multiple population of devices and demand uncertainty.
  • Conference paper
    Green RJ, Strbac, 2015,

    Storage in the energy market

    , IEEE Power and Energy Society General Meeting 2015
  • Journal article
    Chen X, Hou Y, Tan S-C, Lee C-K, Hui SYRet al., 2015,

    Mitigating voltage and frequency fluctuation in microgrids using electric springs

    , IEEE Transactions on Smart Grid, Vol: 6, Pages: 508-515, ISSN: 1949-3053

    Voltage and frequency fluctuation associated with renewable integration have been well identified by power system operators and planners. At the microgrid level, a novel device for the implementation of dynamic load response, which is known as the electric springs (ES), has been developed for mitigating both active and reactive power imbalances. In this paper, a comprehensive control strategy is proposed for ES to participate in both voltage and frequency response control. It adopts the phase angle and amplitude control which respectively adjust the active power and the reactive power of the system. The proposed control strategy is validated using a model established with power system computer aided design/electro-magnetic transient in dc system. Results from the case studies show that with appropriate setting and operating strategy, ES can mitigate the voltage and frequency fluctuation caused by wind speed fluctuation, load fluctuation, and generator tripping wherever it is installed in the microgrid.
  • Journal article
    Merlin MMC, Green TC, 2015,

    Cell capacitor sizing in multilevel converters: cases of the modular multilevel converter and alternate arm converter

    , IET Power Electronics, Vol: 8, Pages: 350-360, ISSN: 1755-4535

    Multilevel converters, such as the modular multilevel converter (MMC) or the alternate arm converter (AAC), rely on charged capacitors in their cells to generate their AC voltage waveform. Since the cell capacitors are physically large and occupy approximately half the cell volume, their capacitance must be kept minimal while limiting the voltage fluctuation caused by the current passing periodically through these capacitors. This study proposes a mathematical model which estimates the energy deviation for the stacks of both the MMC and the AAC during steady‐state operation under any power factor and for AC voltage magnitude fluctuation of up to ±10%. The analysis is then used to calculate the minimum size for the cell capacitors in order to keep their voltage fluctuation within set boundaries for both topologies. The results show that the MMC requires 39 kJ/MVA of capacitive energy storage under sinusoidal modulation but this reduces with triplen injection modulation. The AAC has a lower requirement for storage in its cells of 11 kJ/MVA but the AAC has a six‐pulse DC current ripple which requires a filter estimated to have a further 33% capacitive storage.
  • Report
    Strbac G, Konstantelos I, Moreno Vieyra R, 2015,

    Emerging Modelling Capabilities for System Operations

    , Emerging Modelling Capabilities for System Operations, Publisher: Institute of Engineering and Technology (IET)

    The Institution of Engineering and Technology was commissioned by the Council of Science and Technology(CST) to research the emerging challenges for modelling electricity systems and how Britain’s capabilitieswould need to be adapted to assess electricity system resilience as GB makes the transition to a low carbonelectricity system.
  • Journal article
    Konstantelos I, Strbac G, 2015,

    Valuation of flexible transmission investment options under uncertainty

    , IEEE Transactions on Power Systems, Vol: 30, Pages: 1047-1055, ISSN: 0885-8950

    Significant uncertainty surrounds the future development of electricity systems, primarily in terms of size, location and type of new renewable generation to be connected. In this paper we assess the potential for flexible network technologies, such as phase-shifting transformers, and non-network solutions, such as energy storage and demand-side management, to constitute valuable interim measures within a long-term planning strategy. The benefit of such flexible assets lies not only in the transmission services provided but also in the way they can facilitate and de-risk subsequent decisions by deferring commitment to capital-intensive projects until more information on generation development becomes available. A novel stochastic formulation for transmission expansion planning is presented that includes consideration of investment in these flexible solutions. The proposed framework is demonstrated with a case study on the IEEE-RTS where flexible technologies are shown to constitute valuable investment options when facing uncertainties in future renewable generation development.
  • Journal article
    Keliris C, Polycarpou MM, Parisini T, 2015,

    A robust nonlinear observer-based approach for distributed fault detection of input-output interconnected systems

    , AUTOMATICA, Vol: 53, Pages: 408-415, ISSN: 0005-1098
  • Journal article
    Yin J, Lin D, Lee C-K, Hui SYRet al., 2015,

    A Systematic Approach for Load Monitoring and Power Control in Wireless Power Transfer Systems Without Any Direct Output Measurement

    , IEEE TRANSACTIONS ON POWER ELECTRONICS, Vol: 30, Pages: 1657-1667, ISSN: 0885-8993
  • Journal article
    Zhang C, Zhong W, Liu X, Hui SYRet al., 2015,

    A Fast Method for Generating Time-Varying Magnetic Field Patterns of Mid-Range Wireless Power Transfer Systems

    , IEEE TRANSACTIONS ON POWER ELECTRONICS, Vol: 30, Pages: 1513-1520, ISSN: 0885-8993
  • Journal article
    Parisini T, 2015,

    Untitled

    , IEEE TRANSACTIONS ON CONTROL SYSTEMS TECHNOLOGY, Vol: 23, Pages: 413-414, ISSN: 1063-6536
  • Journal article
    Akhtar Z, Chaudhuri B, Hui SYR, 2015,

    Primary Frequency Control Contribution From Smart Loads Using Reactive Compensation

    , IEEE Transactions on Smart Grid, ISSN: 1949-3061

    Frequency-dependent loads inherently contribute to primary frequency response. This paper describes additional contribution to primary frequency control based on voltage-dependent noncritical (NC) loads that can tolerate a wide variation of supply voltage. By using a series of reactive compensators to decouple the NC load from the mains to form a smart load (SL), the voltage, and hence the active power of the NC load, can be controlled to regulate the mains frequency. The scope of this paper focuses primarily on reactive compensators for which only the magnitude of the injected voltage could be controlled while maintaining the quadrature relationship between the current and voltage. New control guidelines are suggested. The effectiveness of the SLs in improving mains frequency regulation without considering frequency-dependent loads and with little relaxation in mains voltage tolerance is demonstrated in a case study on the IEEE 37 bus test distribution network. Sensitivity analysis is included to show the effectiveness and limitations of SLs for varying load power factors, proportion of SLs, and system strengths.
  • Journal article
    Ng BF, Palacios R, Kerrigan EC, Graham JMR, Hesse Het al., 2015,

    Aerodynamic load control in horizontal axis wind turbines with combined aeroelastic tailoring and trailing-edge flaps

    , Wind Energy, Vol: 19, Pages: 243-263, ISSN: 1095-4244

    This paper presents an aeroservoelastic modeling approach to investigate dynamic load alleviation in large wind turbines with composite blades and trailing-edge aerodynamic surfaces. The tower and rotating blades are modeled using geometrically non-linear composite beams and linearized about reference rotating conditions with potentially arbitrarily large structural displacements. The aerodynamics of the rotor are represented using a linearized unsteady vortex lattice method, and the resulting aeroelastic system is written in a state-space description that is both convenient for model reductions and control design. A linear model of a single blade is then used to design an inline image regulator, capable of providing load reductions of up to 13% in closed loop on the full wind turbine non-linear aeroelastic model. When combined with passive load alleviation through aeroelastic tailoring, dynamic loads can be further reduced to 35%. While the separate use of active flap controls and passive mechanisms for load alleviation has been well-studied, an integrated approach involving the two mechanisms has yet to be fully explored and is the focus of this paper. Finally, the possibility of exploiting torsional stiffness for active load alleviation on turbine blades is also considered.
  • Conference paper
    Puthenpurayil Kunjumuhammed L, Pal BC, 2015,

    Selection of feedback signals for controlling dynamics in future power transmission networks

    , IEEE Power & Energy Society General Meeting, 2015

    This paper deals with the selection of feedback signal(s) that retain the modal behavior of power system electromechanical dynamics under varying operating circumstances. The approach seeks signals that have relatively large magnitude of residue, less variation of the magnitude and phase angle, sufficient gap between the critical pole-zeros, and least sensitive to other modes. The methodology is tested in a 16-machine interconnected power system model with multiple wind farms.
  • Journal article
    Keliris C, Polycarpou MM, Parisini T, 2015,

    Distributed fault diagnosis for process and sensor faults in a class of interconnected input-output nonlinear discrete-time systems

    , International Journal of Control, Vol: 88, Pages: 1472-1489, ISSN: 1366-5820

    This paper presents a distributed fault diagnosis scheme able to deal with process and sensor faults in an integrated way for aclass of interconnected input–output nonlinear uncertain discrete-time systems. A robust distributed fault detection schemeis designed, where each interconnected subsystem is monitored by its respective fault detection agent, and according to thedecisions of these agents, further information regarding the type of the fault can be deduced. As it is shown, a process faultoccurring in one subsystem can only be detected by its corresponding detection agent whereas a sensor fault in a subsystemcan be detected by either its corresponding detection agent or the detection agent of another subsystem that is affected by thesubsystem where the sensor fault occurred. This discriminating factor is exploited for the derivation of a high-level isolationscheme. Moreover, process and sensor fault detectability conditions characterising quantitatively the class of detectable faultsare derived. Finally, a simulation example is used to illustrate the effectiveness of the proposed distributed fault detectionscheme.
  • Journal article
    Chen HT, Choy WCH, Hui SY, 2015,

    Characterization, Modeling, and Analysis of Organic Light-Emitting Diodes With Different Structures

    , IEEE Transactions on Power Electronics, Vol: 31, Pages: 581-592, ISSN: 1941-0107

    This paper demonstrates that organic light-emitting diodes (OLEDs) of different structures can be characterized and modeled using a combination of the photo-electro-thermal (PET) theory and spectral power distribution modeling. The photometric, electrical, thermal, and chromatic properties of OLED devices are incorporated into a model framework so that the performance of the OLED of different structures can be compared. A concept of luminance uniformity over the OLED surfaces is also introduced for comparing OLED with large surface areas. Experimental results are included to verify the OLED models and compare the characteristics of two different OLED samples. Based on the same PET framework, some differences of OLEDs and inorganic LEDs are addressed and discussed.
  • Conference paper
    Jiang J, Astolfi A, 2015,

    Shared-control for the kinematic model of a mobile robot

    , IEEE 53rd Annual Conference on Decision and Control (CDC), Publisher: IEEE, Pages: 62-67

    This paper presents a shared-control algorithm for the kinematic model of a mobile robot. The set of feasible position of the robot is defined by a group of linear inequalities. The shared-control strategy is based on a hysteresis switch and its properties are established by a Lyapunov-like analysis. Simulation results illustrate the effectiveness of the algorithm

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