Design considerations for Fast Frequency Control in the Nordic Synchronous Area

The increasing penetration of converter-interfaced generation and loads in modern power systems significantly reduces inherent mechanical inertia and natural damping, challenging traditional approaches to frequency stability. This paper investigates the evolving system needs associated with decreasing inertia and frequency-dependent load characteristics in the Nordic synchronous area. A method is developed to quantify small disturbance frequency stability requirements as a function of inertia and load damping, using linear control theory and frequency-domain analysis. Complementary measures for Fast Frequency Control (FFC) are consequently evaluated through analysis of both small and large disturbances. Results indicate that current Frequency Containment Reserves (FCR) alone cannot ensure adequate performance and stability margins under low-inertia scenarios, and faster supplementary control is required. Among the investigated measures, a phase-compensated band-pass filter demonstrates the highest efficiency for both small and large disturbance cases. The findings highlight the need for coordinated system-level design of frequency control strategies, considering combined amplitude and phase response.