Research On The Relationship Between The Interations Of UPFC Control And It's Control Operational Condition

Unified Power Flow Controller (UPFC) is the most powerful new-generation FACTS (Flexible AC Transmission Systems) device providing the most advanced control performance. One of its important characteristics is its multiple control functions, including load flow control, voltage regulation and stability enhancement. For each of those control functions, a SISO (Single-input Single-output) is arranged. That has been the current practice of designing UPFC. However, from the point of view of multi-variable control theory, that arrangement is inherently infective, as when multiple SISO controllers are assigned to a MIMO (Multi-input Multi-output) system, stability of closed-loop system cannot be ensured if the transfer function matrix of the system is not diagonally dominant. That means even if each SISO controller can be designed, successful joint operation of multiple SISO controllers cannot be guaranteed. This is so-called problem of interactions among multiple SISO controllers in the MIMO system. Current publication has demonstrated the existence of control interactions among multiple UPFC control functions that are one of problems affect the normal operation of UPFC. In the worst situation, closed-loop UPFC system may become unstable due to the interactions. Hence, it has been of the most frontier research work to study the interactions of UPFC control.This thesis reviews the history and recent advancement in the research on the interactions of FACTS control. On the basis of defining the new concept of control operational condition of UPFC, relationship between the interactions of UPFC control and its control operational condition is systematically studied. In order to exclude the effect of difference in UPFC parameter setting on its control performance when interactions are studied, in the thesis, changes of controllable parameter regions of UPFC with variations of its control operational conditions is calculated, that reveals their relationship more clearly. The New England 10-machine 39-node power system is used in the thesis.