Dynamic Droop Approach for Storage-based Frequency Control

TL;DR

The paper introduces a novel dynamic droop control method for energy storage systems that effectively eliminates frequency Nadir during transients, outperforming traditional virtual inertia and droop control methods in efficiency and capacity requirements.

Contribution

A new control strategy called iDroop is proposed, which completely eliminates frequency Nadir and reduces storage capacity needs compared to existing methods.

Findings

iDroop achieves Nadir elimination with lower gains than virtual inertia.

iDroop requires approximately 40% less storage capacity.

Virtual inertia needs unrealistic gains for Nadir elimination.

Abstract

Transient frequency dips that follow sudden power imbalances --frequency Nadir-- represent a big challenge for frequency stability of low-inertia power systems. Since low inertia is identified as one of the causes for deep frequency Nadir, virtual inertia, which is provided by energy storage units, is said to be one of the solutions to the problem. In the present paper, we propose a new method for frequency control with energy storage systems (ESS), called dynamic droop control (iDroop), that can completely eliminate frequency Nadir during transients. Nadir elimination allows us to perform frequency stability assessment without the need for direct numerical simulations of system dynamics. We make a direct comparison of our developed strategy with the usual control approaches --virtual inertia (VI) and droop control (DC)-- and show that iDroop is more effective than both in eliminating the Nadir. More precisely, iDroop achieves the Nadir elimination under significantly lower gains than virtual inertia and requires almost $40\%$ less storage power capacity to implement the control. Moreover, we show that rather unrealistic control gains are required for virtual inertia in order to achieve Nadir elimination.