Dynamic performance of a unified power flow controller for stabilizing AC transmission systems

This paper presents dynamic control and performance of a UPFC under a fault condition in a dual-feeder transmission system. The transmission system discussed in this paper consists of two feeders in parallel, which are installed between two power stations. When interruption occurs in one of the two feeders, active and reactive power flow are reduced to half because the line impedance doubles. The UPFC is installed in one power station, and keeps the total amount of active power flowing through the dual feeder constant. In this paper, control stability and power-flow regulation under the single-feeder interrupt are theoretically discussed, and are verified by computer simulation and experiments using a 10-kVA laboratory setup. As a result, it is clarified that a conventional control scheme may cause a large amount of overshoot in active and reactive powers after single-feeder interrupt. On the other hand, "advanced control" can control the active and reactive power faster than the power fluctuations, and thus make it possible to eliminate the power variation accompanied by single-feeder interrupt.