arXiv subjects

F. Milano

Publications and source records attributed to F. Milano.

6 recordsLinked to original sources

arXiv2026

Sinusoidality Index

Maintaining sinusoidal or near-sinusoidal operating conditions in electrical systems is essential, as is their accurate assessment. This letter proposes a novel metric, namely the sinusoidality index, which quantifies the instantaneous deviation of the trajectory of an ac voltage vector with respect to a circle under any periodic operating conditions. This metric differs from conventional Fourier-based estimations by accounting for the trajectory of the waveform rather than its spectral decomposition. A variety of examples illustrates the properties of the proposed metric and highlights insights that may not be captured by conventional approaches.

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arXiv2026

Modal Energy for Power System Analysis: Definitions and Requirements

Modal energy provides information complementary to and based on conventional eigenvalues and participation factors for power system modal analysis. However, modal energy definition is not unique. This letter clarifies the definitions and applicability of mainstream modal energy approaches, focusing on their mappings to eigenvalues and to the total system energy. It is shown that these mappings hold only under restrictive conditions, notably system normality, which limits their applicability in inverter-dominated power systems.

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arXiv2026

Instantaneous Frequency in Power Systems using the Teager-Kaiser Energy Operator

This letter develops an instantaneous-frequency (IF) local estimator calculated with the complex Teager-Kaiser energy operator (CTKEO) and the dynamic-signal identity. The contribution is a novel CTKEO-based IF expression that makes the envelope-curvature terms explicit, thus correcting the bias that affects conventional estimators used in power systems. The estimator aligns with complex-frequency (CF) kinematics and admits a geometric interpretation (curvature) without phase unwrapping. This yields an accurate local frequency estimate in operating conditions where magnitude variations contribute non-negligibly to the signal dynamics. Tests on field measurements illustrate the practical behavior of the proposed approach and its consistency with a geometric-frequency benchmark.

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arXiv2025

Theoretical and Experimental Limitations of RoCoF Estimation

A precise estimation of the Rate of Change of Frequency (RoCoF) is crucial for secure power system operation. In fact, RoCoF is strictly related to the amount of the available physical and/or virtual inertia of the system and the severity of the active power unbalance following a disturbance. For this reason, it is widely exploited in different protection systems, e.g., Anti-Islanding, Under Frequency Load Shedding (UFLS) and wide-area protection systems. The new paradigm of modern power systems, with a low-inertia and converter-based generation assets, is increasing the transient severity, making the frequency and the RoCoF estimation more complex and less precise for the actual devices. This work addresses this issue by proposing a numerically robust approach based on concepts inherited from differential geometry and fluid mechanics. The proposed approach is then tested with high-sampling real experimental measurements and used to develop a faster control logic for a RoCoF-based UFLS control scheme. The proposed approach provides information to protections regarding the nature of the contingency which can be used to improve its response.

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arXiv2024

A Complex Frequency-Based Control for Inverter-Based Resources

This paper proposes a novel control for Inverter-based Resources (IBRs) based on the Complex Frequency (CF) concept. The controller's objective is to maintain a constant CF of the voltage at the terminals of the IBR by adjusting its current reference. This current is imposed based on the well-known power flow equation, the dynamics of which are calculated through the estimation of the CF of the voltages of the adjacent buses. Performance is evaluated by analyzing local variations in frequency and magnitude of the voltage, as well as the response of the system's Center of Inertia (CoI) frequency, and then compared with conventional frequency droop, PI voltage controllers and virtual inertia. The case study utilizes the WSCC 9-bus system and a 1479-bus model of the Irish transmission grid and considers various contingencies and sensitivities such as the impact of limiters, delays, noise, R/X ratio, and EMT dynamics. Results show that the proposed scheme consistently outperforms the conventional controllers, leading to significant improvements in the overall dynamic response of the system.

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arXiv2024

Synthetic Discrete Inertia

This letter demonstrates how synthetic inertia can be obtained with the control of flexible discrete devices to keep the power balance of power systems, even if the system does not include any synchronous generator or conventional grid-forming converter. The letter also discusses solutions to cycling issues, which can arise due to the interaction of uncoordinated discrete inertia controllers. The effectiveness, dynamic performance, and challenges of the proposed approach are validated through simulations using modified versions of the WSCC 9-bus test system and of the all-island Irish transmission system.

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