Robustness of Unified Power Flow Controller to the Variations of Control Operating Conditions

Unified power flow controller (UPFC) is of multiple control functions to regulate AC voltage, active power and reactive power flow. Research has found that existence of dynamic interactions among those multiple control functions may result in poor control performance and even closed-loop system instability. This paper investigates the UPFC's controllable parameter region with variations of UPFC control operating conditions as far as UPFC control interactions are concerned. Results in the paper demonstrate that the UPFC's controllable parameter region and existence of interactions change with variations of UPFC control operating conditions. Suggestions are given in the paper to improve UPFC robustness to the variations