Control of a Hybrid Shunt FACTS Compensator for Voltage Collapse Prevention in Interconnected EHV Power Transmission Systems

This article presents the converter topology for a hybrid shunt compensator (HSC) and its control suitable for an extra-high-voltage (EHV) power transmission system that helps to prevent voltage instability/collapse in multimachine interconnected power systems. Similar compensators combining a static VAR compensator (SVC) and a static synchronous compensator (STATCOM) have been proposed in the literature for power factor correction and active filtering, which are issues mostly related to the distribution system. However, for application in EHV transmission and voltage stability, the existing hybrid structures may not be suitable. This article particularly focuses on the prevention of voltage collapse that takes place in large EHV power transmission systems due to the mismatch of system-wide reactive power generation and consumption. The HSC proposed here is formed by the series combination of a STATCOM having a voltage rating of just 0.15 p.u. and an SVC having a voltage rating of 0.85 p.u. A suitable control strategy is formulated for the HSC that results in a modified operating (
$V\text{--}I$
) characteristic enabling the compensator to behave like a STATCOM (with a STATCOM of considerably low voltage rating) and inject constant current even when the voltage at the point of common coupling falls as low as 0.7 p.u.