On-Line Transient Control of Capacitor Switching to Improve System Stability

Switching of series capacitors to improve system stability is of current interest. Investigations indicate that modern control theory might be applied to determine switching of a combination of series capacitors so that the system may be transferred from one state to another in minimum time and in a nonoscillatory manner. In these studies, a simplified voltage-reactance equivalent of the one-machine infinite bus system was used. The material presented in this paper shows that this simplified model does not predict the performance of a one-machine infinite bus system with the accuracy necessary to determine the capacitor switching times so as to achieve the control objectives. However, it is shown that computation accuracy may be improved by including system losses. It appears that in order to apply optimal control techniques it will be necessary to develop more accurate models of the power system components. Also, faster than real time iterative, on-line, computation techniques as simulatedc in this paper should be implemented and used to calculate the switching times. Until these obstacles are overcome, optimal control theory will have little impact upon the power industry.