A preliminary study on the Thevenin equivalent impedance for power systems monitoring

It is an important task to accurately estimate the Thevenin equivalent impedance seen from a load bus for power systems monitoring and control. The purpose of this paper is to investigate the mechanism and characteristics of the Thevenin equivalent impedance in a nonlinear circuit. A general model is introduced for investigating the Thevenin equivalent impedance in an analytical manner. Two typical approaches are presented to approximate the Thevenin equivalent impedance. A simple three bus system is employed to test the two approximate methods. In the simulations, three types of load models, i.e. constant impedance, constant current and constant power, are discussed, respectively, for the load inside the equivalent network. Some interesting phenomena have been observed, and these findings could be likely to bring a new idea to determine the Thevenin impedance for power systems, in an analytical manner.