Shaping Frequency Dynamics in Modern Power Systems with Grid-forming Converters

TL;DR

This paper analyzes frequency dynamics in future power systems with high converter-based generation, contrasting grid-following and grid-forming VSCs. Using small-signal eigenvalue analysis and EMT simulations, it shows that grid-forming converters can induce first-order frequency responses and enhanced damping, especially at high penetration levels, by acting as voltage sources with fast P-f and Q-V control. The study identifies two key oscillation modes—the Synchronisation mode and the Global mode—and demonstrates how converter control parameters and inertia reduction shape these modes in reduced and large-scale IEEE 118-bus systems. The findings highlight the potential of grid-forming converters to reshape system frequency dynamics, while also stressing the need for adequate converter capacity and coordinated control to ensure stable operation during transients.

Abstract

In this paper, frequency dynamics in modern power systems with a high penetration of converter-based generation is analysed. A fundamental analysis of the frequency dynamics is performed to identify the limitations and challenges when the converter penetration is increased. The voltage-source behaviour is found as an essential characteristic of converters to improve the initial frequency derivative of Synchronous Generators (SGs). A detailed small-signal analysis, based on the system's eigenvalues, participation factors and mode shapes, is then performed in a reduced system for different converter penetrations, showing that the flexibility of grid-forming (GFOR) converters as well as the system's inertia reduction may lead to have a more controllable system frequency. First-order frequency responses can be programmed for high converter penetrations, when GFOR operation can impose their dominance over SGs. These results have been validated in the IEEE 118-bus system simulated in PSCAD.

Figures (17)

• Figure 1: Measured frequency probability in Australia. Data from AEMO2023b.
• Figure 2: Frequency dynamics of a conventional power system: (a) Reduced-order model; (b) Effect of SG inertia.
• Figure 3: Frequency dynamics with an $\alpha$ penetration of GFOL VSC: (a) without frequency support ($\beta=0$); (b) with proportional frequency support ($\beta=1$).
• Figure 4: Frequency nadir and RoCoF evolution for different values of VSC penetration ($\alpha$) and proportion of active VSCs in frequency support ($\beta$).
• Figure 5: Power-frequency droop control in GFOR operation.