On the specification of requirements for the activation dynamics of Frequency Containment Reserves

Abstract

The dynamic requirements for the provision of Frequency Containment Reserves (FCR) in Continental Europe are defined in the respective network codes (e.g. System Operation Guideline). However, this definition is precise only for a sudden frequency deviation of ±200 mHz. The requirements for smaller and/or slower frequency deviations are only described indirectly by referring to the case of ±200 mHz. As a result, different interpretations are possible, among which requiring activation dynamics that a) correspond to a linear time-invariant (LTI) system or b) exhibit a constant rate of change of power (RoCoP). This paper assesses the effects of these two different requirement interpretations on FCR providers and system stability by comparing their effect for different frequency deviations. It turns out that the RoCoP interpretation is disadvantageous, as it provides a slower response for large and fast frequency deviations and a fast response for small frequency deviations. Apart from Battery Energy Storage Systems (BESS), most FCR providers cannot perform FCR activation with a fixed RoCoP. In a further step, we consider the effects of the different requirement interpretations on system stability. For a constant RoCoP, it is assumed that the FCR is provided by BESS, while a conventional power plant model is used to implement LTI behavior. The comparison is performed both with model parameters corresponding to the current grid and with model parameters corresponding to a future grid. For each grid model, two scenarios are considered: The first scenario considers active power imbalances caused by load noise only (normal operation), while the second takes an additional significant generation outage into account (contingency). The results show that, in the load noise scenario, FCR activation with constant RoCoP reduces the frequency deviations slightly at the cost of higher total FCR provision and higher maximum FCR activation. However, in case of an additional generation outage, constant RoCoP activation results in a larger maximum frequency deviation, which means that the stability margin of the system is reduced.