Application of UPFC to Enhancing Oscillatory Response of Series-Compensated Wind Farm Integrations

Flexible ac transmission systems, as a key building block of transmission-level smart girds, have shown effective functionalities in promoting the system operation security and service reliability. Facing with series-compensated lines, subsynchronous resonance (SSR) may strike the power system by jeopardizing its stability and mechanical facilities. The operation of such transmission lines is broadening as a direct result of emergent desire to exploit distant wind energy resources in large scales. This paper verifies the capability of unified power flow controller (UPFC) in attenuating SSR in wind farm integrations. SSR is local in its nature; hence, local measurements are merely employed here for controlling the series convertor while wide-area signals could be as well utilized in parallel for other objectives such as inter-area oscillation damping. An equivalent self-excited induction generator (SEIG) represents the wind farm and is connected to the system through a series-compensated line. The UPFC is located at the wind terminal of the linking line; thus, the needed reactive power of SEIG is produced by the shunt branch of UPFC. Both SSR types, namely generator effect and torsional interaction, are examined here. Simulations are carried out on the IEEE first SSR benchmark model integrated with a SEIG wind turbine.