Resumen:
Accurate frequency estimation is critical for the control, monitoring and protection of electrical power systems. This paper introduces the novel concept of Quasi Steady-State (QSS) frequency as a quantity that fills the gap between stationary and instantaneous frequency. QSS frequency coincides with the fundamental frequency of an AC voltage in any stationary conditions, including unbalanced and non-sinusoidal, and is able to capture the time-varying fundamental frequency in transient conditions. The paper also proposes a metric borrowed from fluid dynamics, namely, the time derivative of the circulation, to define the scope of validity of the QSS frequency. Analytical examples as well as a case study based on a fully-fledged EMT model of the IEEE 39-bus system serve to illustrate, respectively, the properties of the QSS frequency and its behavior in transient conditions.
Resumen divulgativo:
Este artículo presenta el concepto de frecuencia de Cuasi-Régimen Permanente (QSS), una nueva magnitud que cubre el vacío entre la frecuencia estacionaria y la instantánea, y que se mantiene válida incluso en condiciones desbalanceadas o no sinusoidales. También se propone una métrica basada en la derivada temporal de la circulación para delimitar su validez, ilustrando sus propiedades mediante ejemplos analíticos y simulaciones.
Palabras Clave: Frequency measurement, filtering, differential geometry, instantaneous frequency, Fourier transform.
Índice de impacto JCR-JIF y cuartil WoS: 5,600 - Q1 (2025)
Referencia DOI:
https://doi.org/10.1109/TCSI.2025.3612501
Publicado en papel: Abril 2026.
Publicado on-line: Septiembre 2025.
Cita:
J. Gutiérrez-Florensa, A. Ortega, L. Sigrist, F. Milano, "Quasi Steady-State Frequency", IEEE Transactions on Circuits and Systems I: Regular Papers, Vol. 73, nº. 4, pp. 2986 - 2998, Abril 2026. [Online: Septiembre 2025] doi: 10.1109/TCSI.2025.3612501
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