Forecast of the system frequency response for underfrequency load shedding

The majority of adaptive underfrequency load shedding schemes are very dependent on an active power imbalance determination, based on a measurement of the initial frequency first time derivative. As this is difficult to perform, it is reasonable to attempt to avoid having to calculate the imbalance. Therefore, an approach to load shedding is used in this paper, which is based on forecast of the system frequency response, using the frequency second time derivative as a source of information. A Newton-method-based approximation and the interpolation of the frequency second time derivative are continuously performed in order to forecast the minimum frequency value using a numerical integration. The scheme has been tested in the dynamic model of Slovenian power system and has shown exceptionally good performance results.