A method for evaluating frequency regulation in an electrical grid

Abstract

The first part of this two-part paper proposes a technique that consists in the measurement, through phasor measurement units, of bus frequency variations to estimate the rate of change of regulated power, and in the definition of a local index that is able to discriminate between devices that modify the frequency at the connection bus and devices that do not. A taxonomy of devices based on their ability to modify locally the frequency is proposed. A byproduct of such an index is to estimate the inertia or equivalent inertia of the monitored device. The proposed index is shown to be a relevant consequence of the concept of frequency divider formula recently published by the authors on the IEEE Transactions on Power Systems. The properties of the proposed index is illustrated through examples based on the synchronous machine and its controllers. The second part of this two-part paper discusses how to determine whether a device connected to the grid is providing inertial response andor frequency control. The proposed technique is based on the index proposed in Part I of this paper. This part first discusses the dynamic behavior in terms of the rate of change of controlled power of a variety of non-synchronous devices that do and do not regulate the frequency. These include passive loads, energy storage systems and thermostatically controlled loads. Then a case study based on a real-world dynamic model of the all-island Irish transmission system discusses an application, based on a statistical analysis, of the proposed technique to wind power plants with and without frequency control. The properties and the robustness with respect to noise and other measurement issues of the proposed technique are also thoroughly discussed.