Stability Analysis of Oscillations in SVCs

Static var compensators (SVCs) have been popularly installed to provide voltage support. It is well known by the grid industry that large voltage control gain may lead to instability, especially in weak grids when the grid impedance becomes large. Analytical models have been developed for eigenvalue analysis. This approach requires tremendous modeling efforts besides the electromagnetic transient (EMT) simulation test bed setup. In this paper, we use measurements obtained from an EMT simulation test bed to extract the linear model that reflects the relationship between SVC’s susceptance command and the point of connection voltage magnitude. Analysis based on the open-loop system consisting of the voltage controller and the learned linear model shows that oscillations are mainly due to time delay introduced by thyristor switching devices and digital control. Increasing voltage control and reducing the system strength push the oscillation mode towards the right half plane (RHP). The measurement-based stability analysis approach provides a simple, straightforward, yet powerful tool to characterize stability issues.