Frequency stability analysis for automatic Frequency Restoration Reserve exchange between asynchronous areas via HVDC interconnectors

Abstract:
This paper assesses the dynamic response of automatic Frequency Restoration Reserve (aFRR) exchange between two synchronous areas interconnected via HVDC links. The interactions between the AC grids are analyzed, highlighting potential issues and instabilities. To address these challenges, this work proposes the introduction of an additional low-pass filter to regulate the correction signals from the Activation Optimization Function (AOF) optimizer, enabling the Transmission System Operator (TSO) to control possible system oscillations. Depending on the scenario, the TSO can choose to use either the setpoint or the measurement signal for calculating the aFRR demand. Simulations of a single HVDC outage show that the AOF optimizer may delay the detection of such outages, further affecting system stability.