Imperial College London


Faculty of EngineeringDepartment of Electrical and Electronic Engineering

Honorary Research Fellow







Electrical EngineeringSouth Kensington Campus





Publication Type

11 results found

Trovato V, Tindemans S, Strbac G, 2017, Understanding aggregate flexibility of thermostatically controlled loads, 12th IEEE Power and Energy Society PowerTech Conference 2017, Publisher: IEEE

Thermostatically controlled loads (TCLs) are an attractive source of responsive demand. This paper aims to provides a better understanding of the relation between thermal properties of TCLs and their suitability to provide energy arbitrage and frequency services. An approximate analysis on the basis of dimensionless parameters is used to visualise the relative abilities of eight classes of TCLs. The results are compared to those obtained from a formal optimisation approach, in the context of a GB case study. Additional studies are performed to investigate the impact of increasingly flexible frequency services and physical variations of TCL thermal models (thermal conductance and temperature deadband).

Conference paper

Trovato V, Martinez Sanz I, Chaudhuri B, Strbac Get al., 2017, Advanced control of thermostatic loads for rapid frequency response in Great Britain, IEEE Transactions on Power Systems, Vol: 32, Pages: 2106-2117, ISSN: 0885-8950

In the Great Britain power system, reduced system inertia (particularly during low demand conditions) and larger possible infeed loss would make grid frequency regulation extremely challenging in future. Traditional primary frequency response could be insufficient to limit the frequency variation within acceptable range. This paper shows that thermostatically controlled loads (TCLs) (domestic refrigerators) can be controlled without real-time communication and in a nondisruptive way to collectively enhance the network frequency response. The aggregated power consumption of TCLs, distributed across the system, could be controlled as a `linear' function of the locally measured frequency and its rate of change. Alternatively, their aggregated consumption could be made to follow a `pre-set' power profile depending on the estimated infeed loss. A novel technique for accurate estimation of infeed loss and consequent postfault TCL power reduction is also proposed. The effectiveness of the two TCL control strategies is compared for primary and secondary frequency response through a case study on a 36 busbar reduced equivalent of the Great Britain power system. The effect of spatial variation of transient frequencies and the time delays in frequency measurement and filtering are considered to show how the TCLs can realistically provide rapid frequency response.

Journal article

Martınez-Sanz IM, Chaudhuri B, Junyent-Ferre A, Trovato V, Strbac Get al., 2016, Distributed vs. Concentrated Rapid Frequency Response Provision in Future Great Britain System, IEEE Power and Energy Society General Meeting, Publisher: IEEE, ISSN: 1944-9933

Two major sources of rapid frequency response(RFR) to counter the reducing system inertia problem of theGreat Britain (GB) system are “synthetic inertia” from windturbines and fast demand response (FDR). In this paper, weconsider a future low inertia scenario to show the effectivenessof RFR provision from the large offshore wind farms (OWFs)planned in the North Sea (concentrated response) against FDRfrom loads spread across the GB system (distributed response).The spatial variation in transient frequencies, which can bepronounced in the aftermath of a disturbance and is criticalfor the response activation of these actuators, is accounted. Casestudies using a reduced GB system model show the effectivenessof distributed FDR and concentrated support from OWFs inproviding RFR when disturbances occur in different areas of thesystem where different inertia levels are present.

Conference paper

Teng F, Trovato V, Strbac G, 2016, Stochastic scheduling with inertia-dependent fast frequency response requirements, IEEE Transactions on Power Systems, Vol: 31, Pages: 1557-1566, ISSN: 0885-8950

High penetration of wind generation will increase the requirement for fast frequency response services as currently wind plants do not provide inertial response. Although the importance of inertia reduction has been widely recognized, its impact on the system scheduling has not been fully investigated. In this context, this paper proposes a novel mixed integer linear programming (MILP) formulation for stochastic unit commitment that optimizes system operation by simultaneously scheduling energy production, standing/spinning reserves and inertia-dependent fast frequency response in light of uncertainties associated with wind production and generation outages. Post-fault dynamic frequency requirements, rate of change of frequency, frequency nadir and quasi-steady-state frequency are formulated as MILP constraints by using the simplified model of system dynamics. Moreover the proposed methodology enables the impact of wind uncertainty on system inertia to be considered. Case studies are carried out on the 2030 Great Britain system to demonstrate the importance of incorporating inertia-dependent fast frequency response in the stochastic scheduling and to indicate the potential for the proposed model to inform reviews of grid codes associated with fast frequency response and future development of inertia-related market.

Journal article

Trovato V, Tindemans SH, Strbac G, 2016, The leaky storage model for optimal multi-service allocation of thermostatic loads, IET Generation Transmission & Distribution, Vol: 10, Pages: 585-593, ISSN: 1751-8687

Collectively, thermostatically controlled loads (TCLs) offer significant potential for short-term demand response. This intrinsic flexibility can be used to provide various ancillary services or to carry out energy arbitrage. This paper introduces an aggregate description of the flexibility of a heterogeneous TCLs as a leaky storage unit, with associated constraints that are derived from the TCL device parameters and quality of service requirements. In association with a suitable TCL control strategy this enables a straightforward embedding of TCL dynamics in optimisation frameworks. The tools developed are applied to the problem of determining an optimal multi-service portfolio for TCLs. A linear optimisation model is constructed for the optimal simultaneous allocation of frequency services and energy arbitrage. In a case study, optimal service allocations are computed for eight representative classes of cold appliances and the results are validated using simulations of individual refrigerators. Finally, it is demonstrated that clustering of appliances with similar capabilities can significantly enhance the flexibility available to the system.

Journal article

Tindemans SH, Trovato V, Strbac G, 2015, Decentralized control of thermostatic loads for flexible demand response, IEEE Transactions on Control Systems Technology, Vol: 23, Pages: 1685-1700, ISSN: 1063-6536

Thermostatically controlled loads (TCLs), such as refrigerators, air-conditioners and space heaters, offer significant potential for short-term modulation of their aggregate power consumption. This ability can be used in principle to provide frequency response services, but controlling a multitude of devices to provide a measured collective response has proven to be challenging. Many controller implementations struggle to manage simultaneously the short-term response and the long-term payback, whereas others rely on a real-time command-and-control infrastructure to resolve this issue. In this paper, we propose a novel approach to the control of TCLs that allows for accurate modulation of the aggregate power consumption of a large collection of appliances through stochastic control. By construction, the control scheme is well suited for decentralized implementation, and allows each appliance to enforce strict temperature limits. We also present a particular implementation that results in analytically tractable solutions both for the global response and for the device-level control actions. Computer simulations demonstrate the ability of the controller to modulate the power consumption of a population of heterogeneous appliances according to a reference power profile. Finally, envelope constraints are established for the collective demand response flexibility of a heterogeneous set of TCLs.

Journal article

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

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.

Conference paper

Trovato V, Tindemans SH, Strbac G, 2014, Security constrained economic dispatch with flexible thermostatically controlled loads, IEEE PES ISGT Europe 2014

Thermostatically controlled loads (TCLs) such as refrigerators and air conditioners are natural candidates for short term demand response. In this paper we quantify the value associated with the TCLs' ability to provide system security and transmission constraint management services. The analysis builds on recent results that enable the aggregate control of TCLs as a leaky storage unit. We incorporate this model in a security constrained economic dispatch (SCED) that minimizes the system operational cost of a two bus-bar system, subject to frequency response and transmission constraints. Further sensitivity studies assess the impact of different penetration levels of controllable loads and transmission flow constraints.

Conference paper

Trovato G, Tindemans SH, Strbac G, 2013, Demand Response Contribution to Effective Inertia for System Security in the GB 2020 Gone Green Scenario, IEEE Innovative Smart Grid Technologies (ISGT) Europe 2013

Conference paper

Trovato V, Tindemans SH, Strbac G, 2013, Controlling the synchronization and payback associated with the provision of frequency services by dynamic demand, 22nd International Conference on Electricity Distribution (CIRED 2013)

Conference paper

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