Effects of load on voltage stability and performance limitations in excitation control

In this paper, voltage unstable phenomena are investigated when synchronous machine is under either manual or automatic excitations. The study shows that the machine under these excitations experience different ways of voltage instability. Moreover, this paper reveals a non-minimum phase characteristic of the machine flux linkage caused by heavy power system load, resulting in voltage instability problem and control performance limitations. Particular emphasis is given to investigate fundamental limitations in excitation control, imposed by open-loop right-half-plane pole. Bode integral technique is used for the investigation