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. 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 lecture consists of two parts. The first part presents an accurate yet simple and computationally inexpensive formula, namely, the frequency divider, that links synchronous machine rotor speeds and bus frequency variations. The second part extends the frequency divider to non-synchronous devices and provides an interpretation of the rate of change of active power injected at a bus. A practical definition of devices that impact on the frequency at their point of connection, namely frequency influencers, is discussed. All concepts are illustrated through examples based on IEEE benchmark systems.

Biography:

Prof. Federico Milano received from the Univ. of Genoa, Italy, the ME and PhD 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 full professor. He has authored 9 books and 350+ papers. He was elevated IEEE Fellow in 2016 for his contributions to power system modeling and simulation, IET Fellow in 2017, and IEEE PES Distinguished Lecturer in 2020. He was the chair of the Technical Program Committee of the PSCC 2024 and Senior Editor of the IEEE Transactions of Power Systems. He is currently secretary of the IEEE Power System Dynamic Performance Committee, member of the PSCC Executive Board and editor in chief of the IET Generation, Transmission & Distribution.