An expert fuzzy control approach to voltage stability enhancement

The voltage stability control problem has become an important concern for utilities transmitting power over long distances. This paper presents a new approach using fuzzy set theory for reactive power control with the purpose of improving the voltage stability of a power system. Voltage stability index and controlling variables are translated into fuzzy set notations to formulate the relation between voltage stability level and controlling ability of controlling devices. Control variables considered are switchable VAR compensators, OLTC transformers and generator excitations. A fuzzy rule based system is formed to select the controllers, their movement direction and step size. The developed fuzzy system is tested on a few simulated practical Indian power systems and modified IEEE 30 bus system. The performance of the fuzzy system is compared with conventional optimization technique and results obtained are encouraging. Results obtained for a 82 node Indian power network and modified IEEE 30 bus system are presented for illustration purposes. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.