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 non-disruptive 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 post-fault TCL power reduction is also proposed. The effectiveness of the two TCL control strategies are 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.

Abstract-Two major sources of rapid frequency response (RFR) to counter the reducing system inertia problem of the Great Britain (GB) system are "synthetic inertia" from wind turbines and fast demand response (FDR). In this paper, we consider a future low inertia scenario to show the effectiveness of RFR provision from the large offshore wind farms (OWFs) planned in the North Sea (concentrated response) against FDR from loads spread across the GB system (distributed response). The spatial variation in transient frequencies, which can be pronounced in the aftermath of a disturbance and is critical for the response activation of these actuators, is accounted. Case studies using a reduced GB system model show the effectiveness of distributed FDR and concentrated support from OWFs in providing RFR when disturbances occur in different areas of the system where different inertia levels are present.

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