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  • 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.
  • Journal article
    Agalgaonkar Y, Pal BC, Jabr RA, 2015,

    Stochastic Distribution System OperationConsidering Voltage Regulation Risks in thePresence of PV Generation

    , IEEE Transactions on Sustainable Energy, Vol: PP, Pages: 1-10, ISSN: 1949-3037

    Variable over voltage, excessive tap counts andvoltage regulator (VR) runaway condition are major operationalchallenges in distribution network while accommodating generationfrom Photovoltaics (PVs). The conventional approach toachieve voltage control based on off-line simulation for voltage setpoint calculation does not consider forecast errors. In this work,a stochastic optimal voltage control strategy is proposed whileconsidering load and irradiance forecast errors. Stochastic operationalrisks such as overvoltage and VR runaway are definedthrough a chance constrained optimization (CCO) problem. Thisclassical formulation to mitigate runaway is further improvedby introducing a stochastic index called the Tap Tail Expectation.Operational objectives such as power losses and excessive tapcount minimization are considered in the formulation. A samplingapproach is proposed to solve the CCO. Along with other voltagecontrol devices, the PV inverter voltage support features arecoordinated. The simulation study is performed using a realisticdistribution system model and practically measured irradianceto demonstrate the effectiveness of the proposed technique.The proposed approach is a useful operational procedure fordistribution system operators. The approach can minimize feederpower losses, avoid voltage violations and alleviate VR runaway.
  • Journal article
    Scarciotti G, Praly L, Astolfi A, 2015,

    Invariance-like theorems and “lim inf” convergence properties

    , IEEE Transactions on Automatic Control, Vol: 61, Pages: 648-661, ISSN: 1558-2523

    Several theorems, inspired by the Krasovskii-LaSalle invariance principle, to establish “lim inf” convergence results are presented in a unified framework. These properties are useful to “describe” the oscillatory behavior of the solutions of dynamical systems. The theorems resemble “lim inf” Matrosov and Small-gain theorems and are based on a “lim inf” Barbalat's Lemma. Additional technical assumptions to have “lim” convergence are given: the “lim inf”/“lim” relation is discussed in-depth and the role of some of the assumptions is illustrated by means of examples.
  • Conference paper
    Trovato V, Tindemans SH, Strbac G, 2015,

    Designing effective frequency response patterns for flexible thermostatic loads

    , 2015 IEEE 15th International Conference on Environment and Electrical Engineering (EEEIC), Publisher: IEEE, Pages: 1003-1008

    Future power systems will have to integrate large amounts of wind and solar generation to drastically reduce CO2 emissions. Achieving this goal comes at the cost of a reduced level of the system inertia and an increased need for fast response services. Previous research has shown the effectiveness of thermostatically controlled loads (TCLs) providing frequency response, and the ability to accurately control the aggregate power consumption of TCLs. In this paper, we explore the design space of frequency response patterns of flexible TCLs. Two distinct frequency response implementations are presented. The first makes the TCLs' power consumption a linear function of system frequency and/or its rate of change; in the second, TCLs respond to a frequency event tracking a pre-programmed reference power profile. Computer simulations illustrate strengths and weaknesses of the proposed implementations in the context of the GB 2020 Gone Green scenario.
  • Journal article
    Mueller MA, Angeli D, Allgoewer F, 2015,

    On Necessity and Robustness of Dissipativity in Economic Model Predictive Control

    , IEEE Transactions on Automatic Control, Vol: 60, Pages: 1671-1676, ISSN: 1558-2523

    In this paper, we study a dissipativity property which was recently used in several results on economic model predictive control to ensure optimal operation of a system at steady-state as well as stability. In particular, we first investigate whether this dissipativity property is not only sufficient, but also necessary for optimal steady-state operation. In the most general case, this is not true; nevertheless, under an additional controllability assumption, we show that dissipativity is in fact necessary. Second, we provide a robustness analysis of the dissipativity property with respect to changes in the constraint set, which can result in a change in the considered supply rate.
  • Journal article
    Chen HT, Tan S-C, Hui SYR, 2015,

    Analysis and Modeling of High-Power Phosphor-Coated White Light-Emitting Diodes With a Large Surface Area

    , IEEE TRANSACTIONS ON POWER ELECTRONICS, Vol: 30, Pages: 3334-3344, ISSN: 0885-8993
  • Conference paper
    Kwan CH, Kkelis G, Aldhaher S, Lawson J, Yates DC, Luk PC-K, Mitcheson PDet al., 2015,

    Link efficiency-led design of mid-range inductive power transfer systems

    , Pages: 1-7
  • Journal article
    Chen B, Pin G, Ng WM, Hui SYR, Parisini Tet al., 2015,

    A parallel prefiltering approach for the identification of a biased sinusoidal signal: theory and experiments

    , International Journal of Adaptive Control and Signal Processing, Vol: 29, Pages: 1591-1608, ISSN: 1099-1115

    The problem of estimating the amplitude, frequency, and phase of an unknown sinusoidal signal from a noisy-biased measurement is addressed in this paper by a family of parallel prefiltering schemes. The proposed methodology consists in using a pair of linear filters of specified order to generate a suitable number of auxiliary signals that are used to estimate—in an adaptive way—the frequency, the amplitude, and the phase of the sinusoid. Increasing the order of the prefilters improves the noise immunity of the estimator, at the cost of an increase of the computational complexity. Among the whole family of estimators realizable by varying the order of the filters, the simple parallel prefilters of orders 2 + 2 and 3 + 3 are discussed in detail, being the most attractive from the implementability point of view. The behavior of the two algorithms with respect to bounded external disturbances is characterized by input-to-state stability arguments. Finally, the effectiveness of the proposed technique is shown both by comparative numerical simulations and by a real experiment addressing the estimation of the frequency of the electrical mains from a noisy voltage measurement.
  • Conference paper
    Pipelzadeh Y, Moreno Vieyra R, Chaudhuri B, Green T, strbac Get al., 2015,

    Role of Smart Grid Technology and Corrective Control in Enhancing Network Capacity Utilisation in Great Britain with HVDC links

    , CIGRE SYMPOSIUM, Publisher: CIGRE

    A range of advanced, technically effective and economically efficient corrective (or postfault) actions has been proposed to release latent transmission network capacity of the existing system and thus reduce network congestion and accommodate increased connection of low-carbon generation. Although the increased use of corrective control that can manage post-fault transmission overloads has proven to be clearly beneficial from an economic perspective, there are concerns related to the consequent stability (angular and voltage) of transmission systems. In this context, this paper demonstrates various corrective control measures (that can be undertaken by Special Protection Schemes –SPS–) including rapid response of generation and demand against double line outages (N-2) under extremely high power transfer conditions. To demonstrate these benefits, case studies are carried out on a detailed (full) dynamic system model of the Great Britain (GB) transmission network in DIgSILENT, which includes the Western Line-Commutated Converter based High Voltage Direct Current (LCC-HVDC). The value of corrective control measures, based on generationand demand response accompanied by Transient Assistive Measures (TAM) such as rapid changes in DC power order to improve system stability is demonstrated. It is shown that such measures can significantly increase the power transfers through the England-Scotland inter-connector while maintaining N-2 security. Moreover, it is demonstrated that although a generation ramp up/down response is naturally slower than a step-change tripping action over generation and demand (tripping actions are preferred in SPS) and therefore more prone to transient instability problems, generation-only operational measures can be deployed to deal with double circuit (N-2) outages under extremely high power transfers, given that the right portfolio of TAM is deployed. Thus TAM can effectively enhance the set of correctivecontrol measures considered b
  • Journal article
    Nanchian S, Majumdar A, Pal BC, 2015,

    Three-Phase State Estimation Using Hybrid Particle Swarm Optimization

    , IEEE Transactions on Smart Grid, Vol: PP, Pages: 1-11, ISSN: 1949-3061

    This paper proposes a method for three-phase stateestimation (SE) in power distribution network including on-loadtap changers (OLTC) for voltage control. The OLTC tap positionsare essentially discrete variables from the SE point ofview. Estimation of these variables in SE presents a formidablechallenge. The proposed methodology combines discrete andcontinuous state variables (voltage magnitudes, angles, and tappositions). A hybrid particle swarm optimization (HPSO) isapplied to obtain the solution. The method is tested on standardIEEE 13- and 123-bus unbalanced test system models. Theproposed algorithm accurately estimates the network bus voltagemagnitudes and angles, and discrete tap values. The HPSO-basedtap estimation provides a more accurate estimation of losses inthe network, which helps in fair allocation of cost of losses inarriving at overall cost of electricity
  • Journal article
    Strbac G, Hatziargyriou N, Lopes JP, Moreira C, Dimeas A, Papadaskalopoulos Det al., 2015,

    Microgrids

    , IEEE Power & Energy Magazine, Vol: 13, Pages: 35-43, ISSN: 1540-7977
  • Journal article
    Tahir F, Jaimoukha IM, 2015,

    Low-complexity polytopic invariant sets for linear systems subject to norm-bounded uncertainty

    , IEEE Transactions on Automatic Control, Vol: 60, Pages: 1416-1421, ISSN: 0018-9286

    We propose a novel algorithm to compute low-complexity polytopic robust control invariant (RCI) sets, along with the corresponding state-feedback gain, for linear discrete-time systems subject to norm-bounded uncertainty, additive disturbances and state/input constraints. Using a slack variable approach, we propose new results to transform the original nonlinear problem into a convex/LMI problem whilst introducing only minor conservatism in the formulation. Through numerical examples, we illustrate that the proposed algorithm can yield improved maximal/minimal volume RCI set approximations in comparison with the schemes given in the literature.
  • Conference paper
    Aldhaher S, Kkelis G, Yates DC, Mitcheson PDet al., 2015,

    Class EF2 inverters for wireless power transfer applications

    , Pages: 1-4

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