Robust linear output feedback control of a synchronous generator

In this article we propose a robust linear output feedback control scheme for the regulation and trajectory tracking tasks of the load angle variable in a widely used, nonlinear, single synchronous generator model. The proposed linear feedback scheme is based on the use of a classical linear feedback controller and a suitably extended high gain linear observer; aiding the linear feedback controller, in two important tasks: 1) accurate estimation of the input-output system model nonlinearities, 2) accurate estimation of the unmeasured phase variables associated with the load angle variable (shaft angular speed deviation, and shaft angular acceleration). These two key pieces of information are used in the proposed feedback controller to a) cancel, as a lumped unstructured time-varying term, the influence of the nonlinearities and b) devise a proper linear output feedback based on the approximate estimates of the phase variables. The robustness of the scheme is tested against a three phase short circuit of significant duration. The proposed, observer-based, feedback controller requires knowledge of only two constant parameters of the model. The closed loop responses are shown to be robust with respect to reasonable deviations of these parameters from their nominal values.