Transient stability augmentation by programmed power angle relationship using Unified Power Flow Controller

Improvement in transient stability can be achieved by adequate system design and discrete supplementary controllers. The emerging Flexible AC Transmission System (FACTS) controllers are considered to be suitable for this purpose due to their speed and flexibility. The Unified Power Flow Controller (UPFC) is a voltage source converter based FACTS controller which injects a series voltage and a shunt current. In this paper, a control strategy is developed to achieve maximal improvement in transient stability using UPFC. It is shown that for a single machine infinite bus system, maximal improvement in transient stability can be achieved by maximizing the electrical power output of the generator w.r.t. the control variables. This result can be extended to multimachine systems and maximizing power flow on a critical line can improve transient stability. The control strategy is evaluated by a simulation study on the 10 generator 39 bus New England system.