Design of synchronous generator excitation controllers in multimachine power systems using inverse Nyquist array

Using a four-machine power system as an example, a basis for a systematic procedure is described for determining the feedback-gain settings of excitation controllers in a multimachine system over a wide spectrum of system-loading conditions. For illustrative purposes, electrical power and speed are used as the local feedback signals on each machine in addition to voltage feedback, whose gain setting is assumed fixed. For a given loading condition the inverse Nyquist array (i.n.a.) method is employed to estimate a range of feedback-gain settings for dynamic stability. For all machines of interest, a set of fixed gain settings is then chosen which provides a satisfactory small-signal dynamic performance over the range of system loading conditions. Some advantages of this application of the i.n.a. method are highlighted.