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  • Journal article
    de Souza JCS, Lessa Assis TM, Pal BC, 2015,

    Data compression in smart distribution systems via singular value decomposition

    , IEEE Transactions on Smart Grid, Vol: 8, Pages: 275-284, ISSN: 1949-3061

    Electrical distribution systems have been experiencingmany changes in recent times. Advances in metering systeminfrastructure and the deployment of a large number of smartmeters in the grid will produce a big volume of data thatwill be required for many different applications. Despite thesignificant investments taking place in the communications infrastructure,this remains a bottleneck for the implementation ofsome applications. This paper presents a methodology for lossydata compression in smart distribution systems using the singularvalue decomposition technique. The proposed method is capableof significantly reducing the volume of data to be transmittedthrough the communications network and accurately reconstructingthe original data. These features are illustrated by resultsfrom tests carried out using real data collected from meteringdevices at many different substations.
  • Journal article
    Zhang X, Green TC, 2015,

    The modular multilevel converter for high step-up ratio DC-DC conversion

    , IEEE Transactions on Industrial Electronics, Vol: 62, Pages: 4925-4936, ISSN: 0278-0046

    High step-up ratio dc-dc converters with megawatt ratings are of interest in wind turbine interfaces and high-voltage direct-current systems. This paper presents a modular multilevel dc-dc converter based on the standard boost converter topology but with the normal single switches replaced by a number of capacitor-clamped submodules. The converter is operated in resonant mode with resonance between submodule capacitors and the arm inductor. A phase-shifted switching arrangement is applied such that there is a constant number, i.e., N, of submodules supporting the high voltage at a time. In this operation mode, the step-up ratio is dependent on the number of submodules and the inductor charging ratio. The converter exhibits scalability without using a transformer and is capable of bidirectional power flow. An application example of a wind turbine interface with a 10 : 1 conversion ratio is demonstrated in simulation. The experimental verification of the concept using a lab-scale prototype is provided.
  • Journal article
    Li S, Zhu G-R, Tan S-C, Hui SYRet al., 2015,

    Direct AC/DC Rectifier With Mitigated Low-Frequency Ripple Through Inductor-Current Waveform Control

    , IEEE TRANSACTIONS ON POWER ELECTRONICS, Vol: 30, Pages: 4336-4348, ISSN: 0885-8993
  • Conference paper
    Judge PD, Chaffey G, Clemow P, Merlin MMC, Green TCet al., 2015,

    Hardware testing of the alternate arm converter operating in its extended overlap mode

    , International High Voltage Direct Current 2015 Conference (HVDC2015)
  • Conference paper
    Jiang J, Astolfi A, 2015,

    Shared-control for the kinematic model of a rear-wheel drive car

    , American Control Conference, Publisher: IEEE, Pages: 1155-1160, ISSN: 0743-1619

    This paper presents a shared-control algorithm for the kinematic model of a rear-wheel drive car, for which the set of feasible Cartesian positions is defined by a group of linear inequalities. The shared-control scheme is based on a hysteresis switch and its properties are established by a Lyapunov-like analysis. Simple numerical examples demonstrate the effectiveness of the shared-control law.
  • Journal article
    Scarciotti G, Astolfi A, 2015,

    Model reduction of neutral linear and nonlinear time-invariant time-delay systems with discrete and distributed delays

    , IEEE Transactions on Automatic Control, Vol: 99, ISSN: 1558-2523

    The problem of model reduction by moment matching for linear and nonlinear differential time-delay systems is studied. The class of models considered includes neutral differential time-delay systems with discrete-delays and distributeddelays. The description of moment is revisited by means of a Sylvester-like equation for linear time-delay systems and by means of the center manifold theory for nonlinear time-delay systems. In addition the moments at infinity are characterized for both linear and nonlinear time-delay systems. Parameterized families of models achieving moment matching are given. The parameters can be exploited to derive delay-free reduced order models or time-delay reduced order models with additional properties, e.g. interpolation at an arbitrary large number of points. Finally, the problem of obtaining a reduced order model of an unstable system is discussed and solved.
  • Journal article
    Aldhaher S, yates D, Mitcheson P, 2015,

    Modelling and Analysis of Class EF and Class E/F Inverters with series-tuned resonant networks

    , IEEE Transactions on Power Electronics, Vol: 31, Pages: 3415-3430, ISSN: 0885-8993

    Class EF and Class E/F inverters are hybrid inverters that combine the improved switch voltage and current waveforms of Class F and Class F-1 inverters with the efficient switching of Class E inverters. As a result, their efficiency, output power and power output capability can be higher in some cases than the Class E inverter. Little is known about these inverters and no attempt has been made to provide an in depth analysis on their performance. The design equations that have been previously derived are limited and are only applicable under certain assumptions. This paper is the first to provide a comprehensive set of analytical analysis of Class EF and Class E/F inverters. The Class EF2 inverter is then studied in further detail and three special operation cases are defined that allow it to either operate at maximum power-output capability, maximum switching frequency or maximum output power. Final design equations are provided to allow for rapid design and development. Experimental results are provided to confirm the accuracy of the performed analysis based on a 23W Class EF2 inverter at 6.78MHz and 8.60MHz switching frequencies. The results also show that the Class EF2 inverter achieved an efficiency of 91% compared to a 88% efficiency when operated as a Class E inverter.
  • Conference paper
    Tindemans SH, Strbac G, 2015,

    Visualising risk in generating capacity adequacy studies using clustering and prototypes

    , IEEE Power and Energy Society General Meeting, 2015, Publisher: IEEE

    Generating capacity adequacy studies play a significantrole in long term capacity planning. Risks of capacitydeficits are usually reported in the form of one or more averagequantities, which cannot fully convey the nature of the risksbeing faced. Chronological Monte Carlo simulations may be usedto construct comprehensive multi-dimensional risk profiles, butsuch profiles tend to be difficult to interpret. This paper proposesthe use of a clustering method to partition the risk profile intoclusters of similar outcomes with associated probabilities. Theresults are presented in accessible tabular form, and prototypicalscenarios can be analysed in detail to provide further insight.
  • Conference paper
    Mylvaganam T, Astolfi A, 2015,

    Control of Microgrids Using a Differential Game Theoretic Framework

    , Conference on Decision and Control
  • Journal article
    Palladino M, Vinter RB, 2015,

    Regularity of the Hamiltonian Along Optimal Trajectories

    , SIAM Journal on Control and Optimization, Vol: 53, Pages: 1892-1919, ISSN: 1095-7138

    This paper concerns state constrained optimal control problems, in which the dynamic constraint takes the form of a differential inclusion. If the differential inclusion does not depend on time, then the Hamiltonian, evaluated along the optimal state trajectory and the co-state trajectory, is independent of time. If the differential inclusion is Lipschitz continuous, then the Hamiltonian, evaluated along the optimal state trajectory and the co-state trajectory, is Lipschitz continuous. These two well-known results are examples of the following principle: the Hamiltonian, evaluated along the optimal state trajectory and the co-state trajectory, inherits the regularity properties of the differential inclusion, regarding its time dependence. We show that this principle also applies to another kind of regularity: if the differential inclusion has bounded variation w.r.t. time, then the Hamiltonian, evaluated along the optimal state trajectory and the co-state trajectory, has bounded variation. Two applications of these newly found properties are demonstrated. One is to derive improved conditions which guarantee the nondegeneracy of necessary conditions of optimality in the form of a Hamiltonian inclusion. The other application is to derive new conditions under which minimizers in the calculus of variations have bounded slope. The analysis is based on a recently proposed, local concept of differential inclusions that have bounded variation w.r.t. the time variable, in which conditions are imposed on the multifunction involved, only in a neighborhood of a given state trajectory.
  • Conference paper
    Boem F, Xu Y, Fischione C, Parisini Tet al., 2015,

    A distributed pareto-optimal dynamic estimation method

    , 2015 European Control Conference (ECC 2015), Publisher: IEEE, Pages: 3673-3680

    In this paper, a novel distributed model-based prediction method is proposed using sensor networks. Each sensor communicates with the neighboring nodes for state estimation based on a consensus protocol without centralized coordination. The proposed distributed estimator consists of a consensus-filtering scheme, which uses a weighted combination of sensors information, and a model-based predictor. Both the consensus-filtering weights and the model-based prediction parameter for all the state components are jointly optimized to minimize the variance and bias of the prediction error in a Pareto framework. It is assumed that the weights of the consensus-filtering phase are unequal for the different state components, unlike consensus-based approaches from literature. The state, the measurements, and the noise components are assumed to be individually correlated, but no probability distribution knowledge is assumed for the noise variables. The optimal weights are derived and it is established that the consensus-filtering weights and the model-based prediction parameters cannot be designed separately in an optimal way. The asymptotic convergence of the mean of the prediction error is demonstrated. Simulation results show the performance of the proposed method, obtaining better results than distributed Kalman filtering.
  • Conference paper
    Giannelos S, Konstantelos I, Strbac G, 2015,

    Option value of Soft Open Points in distribution networks

    , IEEE Powertech, Publisher: IEEE

    We propose a novel stochastic planning model thatconsiders investment in conventional assets as well as in SoftOpen Points, as a means of treating voltage and thermalconstraints caused by the increased penetration of renewabledistributed generation (DG) sources. Soft Open Points areshown to hold significant option value under uncertainty;however, their multiple value streams remain undetected undertraditional deterministic planning approaches, potentiallyundervaluing this technology and leading to a higher risk ofstranded assets.
  • Journal article
    Strbac G, Konstantinidis CV, Moreno R, Konstantelos I, Papadaskalopoulos Det al., 2015,

    It's All About Grids

    , IEEE POWER & ENERGY MAGAZINE, Vol: 13, Pages: 61-75, ISSN: 1540-7977
  • Conference paper
    Cheng C, Evangelou SA, Arana C, Dini Det al., 2015,

    Active Variable Geometry Suspension robust control for improved vehicle ride comfort and road holding

    , American Control Conference (ACC), 2015, Publisher: IEEE, Pages: 3440-3446, ISSN: 0743-1619

    This paper investigates the design of robust ℋ∞ control for road vehicle Series Active Variable Geometry Suspension (SAVGS). The objective is to improve ride comfort and road holding, while guaranteeing operation inside existing physical constraints. The study utilizes a nonlinear quarter car model that represents accurately the vertical dynamics and geometry of one quarter of a high performance car with a double wishbone suspension. The control objective is to reduce the body vertical acceleration, tire deflection and suspension travel under the impact of road perturbations. Therefore, the selection of the weighting functions for a linear ℋ∞ control, designed for the linearized quarter car, is based on these objectives. The proposed controller is then applied to the nonlinear quarter car model and investigated by nonlinear simulation for a range of road disturbance inputs. The results show that the designed controller when applied on the SAVGS is effective in improving the vehicle ride comfort and road holding.
  • Journal article
    Ye Y, Papadaskalopoulos D, Strbac G, 2015,

    Factoring Flexible Demand Non-Convexities in Electricity Markets

    , IEEE TRANSACTIONS ON POWER SYSTEMS, Vol: 30, Pages: 2090-2099, ISSN: 0885-8950
  • Journal article
    Feng Z, Kerrigan EC, 2015,

    Latching-Declutching Control of Wave Energy Converters Using Derivative-Free Optimization

    , IEEE Transactions on Sustainable Energy, Vol: 6, Pages: 773-780, ISSN: 1949-3029

    We consider predictive control of a wave energy converter(WEC) that can switch between three modes: 1) powergeneration; 2) declutched with no power generation; or 3) latchedwith zero velocity. We propose a formulation that turns the optimalcontrol problem into a small dimensional discrete optimizationproblem, where the only decision variables are bounds onthe latching time and power take-off (PTO) time, whereas theobjective function is computed from the trajectory of a hybridsystem with linear dynamics in each sample interval. The optimizationproblem is solved using a novel derivative-free algorithmthat exploits the quantization of the decision variables in orderto reduce the number of function evaluations. Two closed-loopformulations are also studied within a receding horizon implementation:the first one uses past wave information and can double theenergy generation compared to the uncontrolled case, while thesecond formulation uses predictions of future waves and is able toresult in a further increase in energy generation. The benefits ofcodesigning the physical system and controller is compared to thesequential approach of first optimizing the physical system withoutcontrol, followed by controller design.
  • Journal article
    Zhong WX, Hui SYR, 2015,

    Maximum energy efficiency tracking for wireless power transfer systems

    , IEEE Transactions on Power Electronics, Vol: 30, Pages: 4025-4034, ISSN: 0885-8993

    A method for automatic “maximum energy efficiency tracking” operation for wireless power transfer (WPT) systems is presented in this paper. Using the switched-mode converter in the receiver module to emulate the optimal load value, the proposed method follows the maximum energy efficiency operating points of a WPT system by searching for the minimum input power operating point for a given output power. Because the searching process is carried out on the transmitter side, the proposal does not require any wireless communication feedback from the receiver side. The control scheme has been successfully demonstrated in a two-coil system under both weak and strong magnetic coupling conditions. Experimental results are included to confirm its feasibility.
  • Conference paper
    Sootla A, Oyarzun DA, Angeli D, Stan GBet al., 2015,

    Shaping Pulses to Control Bi-Stable Biological Systems

    , American Control Conference 2015, Publisher: IEEE, Pages: 3138-3143

    In this paper, we present a framework for shaping pulses to control biological systems, and specifically systems in synthetic biology. By shaping we mean computing the magnitude and the length of a pulse, application of which results in reaching the desired control objective. Hence the control signals have only two parameters, which makes these signals amenable to wetlab implementations. We focus on the problem of switching between steady states in a bistable system. We show how to estimate the set of the switching pulses, if the trajectories of the controlled system can be bounded from above and below by the trajectories of monotone systems. We then generalise this result to systems with parametric uncertainty under some mild assumptions on the set of admissible parameters, thus providing some robustness guarantees. We illustrate the results on some example genetic circuits.
  • Conference paper
    Mylvaganam T, Astolfi A, 2015,

    A differential game approach to formation control for a team of agents with one leader

    , American Control Conference
  • Journal article
    Junyent-Ferre A, Pipelzadeh Y, Green TC, 2015,

    Blending HVDC-link energy storage and offshore wind turbine inertia for fast frequency response

    , IEEE Transactions on Sustainable Energy, Vol: 6, Pages: 1059-1066, ISSN: 1949-3029

    This paper explores the benefits of combining the dc-link energy storage of a voltage source converter-based high-voltage dc (VSC-HVDC) link and the kinetic energy storage from wind turbines to facilitate in fast primary frequency control and system inertia to an ac network. Alongside physical and analytical justifications, a method is proposed which blends the energy stored in the HVDC link with the power control capabilities of the wind turbines to provide frequency response that is fast while not requiring excessive volume of capacitance nor demanding performance requirements on the wind turbines.
  • Conference paper
    Chaffey G, Green TC, 2015,

    Reduced DC circuit breaker requirement on mixed converter HVDC networks

    , PowerTech Eindhoven 2015, Publisher: IEEE

    Recently proposed meshed HVDC networks include both converters and DC circuit breakers, and the fault currents experienced and therefore the capacity requirement of circuit breakers are dependent on the topology of converters used on the network. This paper analyses the difference in fault currents seen in various network configurations utilising fault-feeding and fault-blocking converters. Results are presented showing the reduced fault currents seen in the regions of the DC network where fault current limiting converters have been implemented, which could have an impact on the topology, current rating and therefore size and cost of the circuit breaker.
  • Conference paper
    Judge PD, Green TC, 2015,

    Dynamic thermal rating of a Modular Multilevel Converter HVDC link with overload capacity

    , PowerTech Eindhoven 2015, Publisher: IEEE

    The power rating of Modular Multilevel Converter based HVDC has increased rapidly over the past decade, with individual links in the gigawatt power range now technically feasible and further power increases on the horizon. Such large links may be required to provide ancillary services such as fast frequency response or emergency power re-routing in the event of a system disturbance. Providing such services may require converters to be designed with overload capacity. This paper examines how the thermal aspects of semiconductor devices may impact the operation of such converters and how the exploitation of short-term thermal dynamics may lead to dynamic overload rating.
  • Conference paper
    Tindemans SH, Trovato V, Strbac G, 2015,

    Frequency control using thermal loads under the proposed ENTSO-E Demand Connection Code

    , PowerTech 2015, Publisher: IEEE, Pages: 1-6

    Thermal loads such as refrigerators and electric space heaters use temperature hysteresis controllers that are insensitive to small temperature fluctuations. This results in an ability to modulate their power consumption, thus providing cost-effective frequency support, balancing services and energy arbitrage. In order to partially realise these benefits, ENTSO-E has proposed a mandatory frequency support service for thermal loads in its Network Code on Demand Connection. This is to be implemented as a proportional shift of the setpoint temperature in accordance with frequency deviations. In this paper we argue that this implementation choice results in an unpredictable response that depends strongly on controller details. Furthermore, it restricts the flexibility to implement advanced controllers that deliver multiple services simultaneously. We present a case study that demonstrates very different frequency response patterns from three controllers that are each compatible with the proposed Code. Alternative implementations of the code and controllers are presented to illustrate the scope for improvement.
  • Conference paper
    Calvo JL, Ramirez Torrealba PJ, Tindemans S, Strbac Get al., 2015,

    Cost-Benefit Analysis of Unreliable System Protection Scheme Operation

    , IEEE PowerTech 2015, Publisher: IEEE

    System Protection Schemes (SPS) have the potential to greatly enhance the utilization of the network, often by automatically disconnecting generators in response to contingency events. However, malfunctions of such systems may expose the system to harmful blackouts. The operation of unreliable SPS is therefore subject to a cost-benefit balance between the benefits of increased system utilization and the risk of outages. This paper studies this trade-off in a year-round basis. The problem is firstly stated from a centralized perspective to probabilistically minimize the operational costs for a whole operating year. A case study based on a basic simple representation of the Great Britain system is considered. The results show great annual benefits from equipping the SPS with multiple generation disconnection systems, which are mainly associated with critical operating conditions. However, it is demonstrated that redundant SPS configurations do not necessarily reduce the levels of operational risk exposure.
  • Journal article
    Anagnostou G, Pal BC, 2015,

    Impact of Overexcitation Limiters on the Power System Stability Margin Under Stressed Conditions

    , IEEE Transactions on Power Systems, Vol: 31, Pages: 2327-2337, ISSN: 1558-0679

    This paper investigates the impact of the overexcitation limiters (OELs) on the stability margin of a power system which is operating under stressed conditions. Several OEL modeling approaches are presented and the effect of their action has been examined in model power systems. It is realized that, more often than not, OEL operating status goes undetected by existing dynamic security assessment tools commonly used in the industry. It is found that the identification and accurate representation of OELs lead to significantly different transient stability margins. Unscented Kalman filtering is used to detect the OEL activation events. In the context of stressed system operation, such quantitative assessment is very useful for system control. This understanding is further reinforced through detailed studies in two model power systems.
  • Journal article
    Arana C, Evangelou SA, Dini D, 2015,

    Series Active Variable Geometry Suspension application to chassis attitude control

    , IEEE/ASME Transactions on Mechatronics, Vol: PP, ISSN: 1083-4435

    This paper explores the application of the recently introduced Series Active Variable Geometry Suspension (SAVGS) to the control of chassis attitude motions and the directional response of cars. A co-design methodology, involving a component dimensioning framework and a multi-objective control scheme, is developed to maximize the SAVGS control capabilities while respecting vehicle and actuator design constraints. The dimensioning framework comprises: a steady-state mathematical model based on the principle of virtual work; a parameter sensitivity analysis that sheds light on the dependencies that exist between the properties of the passive suspension, the SAVGS and the chassis; and an algorithm to size the main SAVGS components for any given vehicle and steady-state performance objectives. The general multi-objective control scheme is presented for general application, and the particular case of combined chassis attitude control and overturning couple distribution control is developed in detail. The proposed scheme is subsequently applied to a high performance sports car and a fully laden SUV and tested under a wide range of operating conditions through the simulation of standard open-loop maneuvers. Results demonstrate the SAVGS potential to favorably regulate the attitude motions and directional response in both vehicle classes.
  • Conference paper
    Ustinova T, Woolf M, Ortega Calderon JE, Bilton M, O'Brien H, Tindemans S, Djapic P, Strbac Get al., 2015,

    Analysis of Customers' Performance in Industrial & Commercial Demand Side Response Trials

    , 23rd International Conference on Electricity Distribution (CIRED 2015)
  • Conference paper
    Schofield J, Carmichael R, Tindemans S, Woolf M, Bilton M, Strbac Get al., 2015,

    Experimental validation of residential consumer responsiveness to dynamic time-of-use pricing

    , 23rd International Conference on Electricity Distribution (CIRED)

    This paper describes the first analysis from the LowCarbon London (LCL), residential dynamic time-of-use(dToU) pricing trial that took place in the London areaduring 2013. High price induced peak reductions fornetwork constraint management are investigatedalongside the temporal availability of demand responsefor supply balancing. By examining both these use caseswe identify potential conflicts between network andsystem objectives. Demand response results are stratifiedby a ranking metric for engagement with the dToU tariffas well as household occupancy and socio-economicclassification.
  • Journal article
    Papadaskalopoulos D, Strbac G, 2015,

    Nonlinear and Randomized Pricing for Distributed Management of Flexible Loads

    , IEEE Transactions on Smart Grid, Vol: 7, Pages: 1137-1146, ISSN: 1949-3061

    Price-based management of distributed energy resources within microgrids is continuously gaining ground due to scalability and privacy limitations of centralized architectures. However, the concentration of flexible loads' response to the lowest-priced periods yields inefficient solutions. A previously proposed measure imposing a flexibility restriction on flexible loads might raise acceptability and feasibility concerns by the users. This paper develops a novel fully price-based approach where this hard restriction is replaced by a soft nonlinear price signal. This signal is customized to the operating properties of the different flexible load types by penalizing the square of the demand and the duration of cycle delay of loads with continuously adjustable power levels and deferrable cycles, respectively. This approach is shown to produce more efficient solutions than the flexibility restriction measure for both types of loads. For the latter type, randomization of the nonlinear prices brings additional benefits, especially in low operating diversity cases. These contributions are supported by case studies on a microgrid test system with electric vehicles and wet appliances used as representative examples of the above flexible load types.
  • Journal article
    Trutnevyte E, Strachan N, Dodds PE, Pudjianto D, Strbac Get al., 2015,

    Synergies and trade-offs between governance and costs in electricity system transition

    , Energy Policy, Vol: 85, Pages: 170-181, ISSN: 1873-6777

    Affordability and costs of an energy transition are often viewed as the most influential drivers. Conversely, multi-level transitions theory argues that governance and the choices of key actors, such as energy companies, government and civil society, drive the transition, not only on the basis of costs. This paper combines the two approaches and presents a cost appraisal of the UK transition to a low-carbon electricity system under alternate governance logics. A novel approach is used that links qualitative governance narratives with quantitative transition pathways (electricity system scenarios) and their appraisal. The results contrast the dominant market-led transition pathway (Market Rules) with alternate pathways that have either stronger governmental control elements (Central Co-ordination), or bottom-up proactive engagement of civil society (Thousand Flowers). Market Rules has the lowest investment costs by 2050. Central Co-ordination is more likely to deliver the energy policy goals and possibly even a synergistic reduction in the total system costs, if policies can be enacted and maintained. Thousand Flowers, which envisions wider participation of the society, comes at the expense of higher investment and total system costs. The paper closes with a discussion of the policy implications from cost drivers and the roles of market, government and society.

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