Designing a Robust Controller to Damp Sub-synchronous Oscillations in Power Systems

Series compensation using capacitor banks is a common technique used in power transmission systems, to improve the power transferring capability. However, it may lead to the generation of some natural frequencies due to the combination of inductor and capacitor. These frequencies are called as sub-synchronous frequencies which are below the power frequency of the power systems. They can give rise to sub-synchronous resonance (SSR). The SSR can cause physical damages to the power system equipment unless it is detected and mitigated prudently. This paper presents a robust controller which can be used to damp undesirable sub-synchronous oscillations. The small signal model required to design the controller is constructed using dynamic phasor approach. The performance of the controller is demonstrated using IEEE first benchmark model (FBM) for SSR studies. It's shown that the proposed robust controller satisfactorily work under different operating conditions.