February 3, 2021 - Webinar: The role of “frequency” in low-inertia power systems

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    The Role of “Frequency” in Low-Inertia Power Systems

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    The role of “frequency” in low-inertia power systems

    The conventional power system model for transient stability analysis is based on the assumption of quasi-steady-state phasors for voltages and currents. The crucial hypothesis on which such a model is defined is that the frequency required to define all phasors and system parameters is constant and equal to its nominal value. This model is appropriate as long as only synchronous machines regulate the system frequency through standard primary and secondary frequency regulators. In recent years, however, an increasing number of devices other than synchronous machines are expected to provide frequency regulation. These include, among others, distributed energy resources such as wind and solar. However, these devices do not generally impose the frequency at their connection point with the grid. There is thus, from a modeling point of view, the need to define with accuracy the local frequency at every bus of the network.

    The webinar is divided into three parts. The first part presents an accurate yet simple and computationally inexpensive formula, namely, the frequency divider, to estimate such frequencies and, thus, improve the fidelity of the conventional power system model for transient stability analysis. The second part focuses on relevant applications of the frequency divider, namely, the estimation of the rotor speeds of synchronous machines and of the center of inertia by means of phasor measurement units as well as the determination of participation factors of synchronous machines to local bus frequency variations. Finally, the third part extends the estimation problem to non-synchronous devices and provides a novel interpretation of the rate of change of power injected at a bus. A practical definition of devices that impact the frequency at their point of connection, namely frequency influencers, is proposed. Relevant applications to the estimation of the parameters of voltage-dependent loads as well as the location of forced oscillations are outlined. The results of several case studies serve to illustrate the behavior of the frequency divider formula as well as the robustness against noise and bad data of the estimation of machine rotor speeds and the utilization of the concept of frequency influencer to identify non-synchronous devices that provide fast frequency response to the system.


    About the Presenter:


    Prof. Federico Milano

    School of Electrical & Electronic Engineering

    University College Dublin

    Belfield, Dublin 4, Ireland

    E-mail: federico.milano[at]ucd.ie (use @ instead of [at])

    Federico Milano received from the Univ. of Genoa, Italy, the ME and Ph.D. in Electrical Eng. in 1999 and 2003, respectively. From 2001 to 2002 he was with the University of Waterloo, Canada, as a Visiting Scholar. From 2003 to 2013, he was with the University of Castilla-La Mancha, Spain. In 2013, he joined the University College Dublin, Ireland, where he is currently a Professor of Power Systems Control and Protection. He has authored and co-authored 8 books and about 220 papers and book chapters. He was elevated to IEEE Fellow in 2016 for his contributions to power system modeling and simulation, and to IET Fellow in 2017. He has been an editor of several international journals published by IEEE, IET, Elsevier, and Springer, including the IEEE Transactions of Power Systems and the IET Generation, Transmission & Distribution. He is also an IEEE PES Distinguished Lecturer, since 2020.

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