Enhancement of power system damping using VSC-based series connected FACTS controllers

An equivalent model is proposed to analyse the capabilities of voltage source converter (VSC)-based series connected flexible AC transmission system (FACTS) controllers of various types to damp power system oscillations. A universal control strategy using a fuzzy logic method is developed for controlling these VSC-based series connected FACTS controllers. Only the magnitude of the injected voltage needs to be controlled, along with its phase angle which is always set to be constant at pi/2 with respect to different reference voltage vectors for the different controllers. Local measurable signal - voltage phase angle difference between two local buses is selected as an input base. Two inputs, namely the speed rate and acceleration, derived from the phase angle difference, are required for the fuzzy controller, which is robust and easy to tune, to damp power system oscillations. Case studies for a single machine infinite bus (SMIB) and two-machine test systems are conducted at the switch level using the well-established PSCAD/EMTDC software package.