Visit of Prof. Federico Milano
On 8th September Prof. Federico Milano, from University College Dublin, held a IEEE PES Distinguished Lecture on the topic "Low Inertia Systems: Complex Frequency and Simple Control" at the Institute for Technical Physics. The lecture was followed by more than 20 guests in the room and 50 guests online from overall Germany. It provided an overview of frequency control problems and solutions in case of high penetration of renewable energy sources and thus low inertia systems. At the end of the lecture, he introduced an interesting new concept of "complex frequency", able to estimate istantaneously the frequency value and improve any frequency control actions. The abstract of the lecture can be found here below:
Abstract
The conventional power system model for transient stability analysis is based on the assumption of quasisteadystate 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 lectures presents the definition of “complex frequency” and poses the basis of a set of equations that link this new quantity with the active and reactive power injections at network buses. These relationships allow defining how device models and their controllers impact the frequency at their point of connection. This is particularly relevant in the context of lowinertia systems where the frequency support has to be provided by power electronic converters and devices other than conventional synchronous power plants. All concepts are illustrated through examples based on IEEE benchmark systems.”

