Improvement of system security with unified-power-flow controller at suitable locations under network contingencies of interconnected systems

The operation and planning of large interconnected power systems are becoming increasingly complex. To maintain security of such systems, it is desirable to estimate the effect of contingencies and plan suitable measures to improve system security/stability. The paper presents an approach for selection of unified-power-flow-controller (UPFC-) suitable locations considering normal and network contingencies after evaluating the degree of severity of the contingencies. The ranking is evaluated using composite-criteria-based fuzzy logic for eliminating masking effects. The fuzzy approach, in addition to real-power loadings and bus-voltage violations, also used voltage-stability indexes at the load buses as the post-contingent quantities to evaluate the network-contingency ranking. The selection of UPFC-suitable locations uses the criteria on the basis of improved system security/stability. The proposed approach for selection of UPFC-suitable locations has been tested under simulated conditions on a few power systems and the results for a 205-node real-life equivalent regional-power-grid system of three interconnected utility systems are presented for illustration purposes.