Abstract

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.

Highlights

  • I N GREAT Britain (GB), the system operator, National Grid (NG), is responsible for maintaining the transient frequency deviation within 49.2 Hz following large infrequent infeed losses [1]

  • This paper enables the controller for fast frequency response provision while addressing in detail specific implementation requirements

  • The Thermostatically Controlled Loads (TCLs) response is activated by the frequency- and rate of change of frequency (RoCoF)-based criteria but the amount of response does not depend on the measured frequency signals and/or RoCoF unlike the Linear Controller (LC)

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Summary

INTRODUCTION

I N GREAT Britain (GB), the system operator, National Grid (NG), is responsible for maintaining the transient frequency deviation within 49.2 Hz following large infrequent infeed losses [1]. The second contribution of this paper is proposing a novel technique for accurate estimation of infeed loss, which is critical while using a PSSC This technique estimates the infeed loss accurately similar to the technique reported in [31], but it ensures the desired post-fault reduction in aggregate power consumption of the distributed TCLs. The performance of TCL support has to be validated by the system operator in a realistic multi-machine power system model before considering TCLs a reliable source of response services. The third contribution of this paper is the demonstration of the effectiveness of individual distributed TCLs towards providing rapid frequency response through a case study on a 36 busbar reduced equivalent of the GB power system.

BASICS OF TCL CONTROL STRATEGY
FREQUENCY RESPONSE PROVISION FROM TCLS
Activation of TCL Response
Autonomous versus Semiautonomous Operation of TCLs
THE LINEAR CONTROLLER
THE PRESET SHAPE CONTROLLER
Estimation of Infeed Loss
The Control Law
REDUCED EQUIVALENT OF THE GB POWER SYSTEM
SIMULATION RESULTS
Frequency Response from TCLs
Infeed Loss Estimation for PSSC
Method Estimation error Aggregate TCL response
LC Performance for Different Infeed Losses
VIII. CONCLUSION

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