Performance assessment of Synchronous Condensers vs Voltage Source Converters providing grid-forming functions

TL;DR

This paper compares synchronous condensers and voltage source converters with grid-forming control in power systems, analyzing their dynamic responses and contributions to system stability through detailed simulations.

Contribution

It provides a detailed comparison of SC and VSC grid-forming devices, highlighting their performance differences in transient and short-term responses.

Findings

Both devices perform similarly over seconds.

SC provides better initial stiffness after disturbances.

VSC offers faster resynchronization.

Abstract

Having sufficient grid-forming sources is one of the necessary conditions to guarantee the stability in a power system hosting a very large share of inverter-based generation. The grid-forming function has been historically fulfilled by synchronous machines. However, with the appropriate control, it can also be provided by voltage source converters (VSC). This work presents a comparison between two technologies with grid-forming capability: the VSC with a grid-forming control coupled with an adequate energy storage system, and the synchronous condensers (SC). Both devices are compared regarding their inertial response, as well as their contribution to the system strength and short-circuit current for an equivalent capacity expressed in terms of apparent power and inertial reserve. Their behaviour following grid disturbances is assessed through time-domain simulations based on detailed electromagnetic transient (EMT) models. The results show that both devices achieve similar performance in the time-scale of seconds. For shorter time-windows, however, they present a different behavior: the SC ensures a better stiffness in the first tens of ms following the disturbance, while the VSC offers a faster resynchronization.