The system under consideration is shown in block diagram form in Fig. 1.1. P denotes a given system, usually called the plant, whose output is y and whose inputs are the controller output u and disturbance d (for example P is the model of an airplane whose output is its flight path, y, due to its control surface variations, u, and wind disturbances d). Fr is an external command. G is the controller whose tasks, as will be shown in the next section are (i) reduction of the plant output response, y, to disturbance d; and (ii) reduction of the response variation, y, from the desired output, if the plant deviates from its assumed model P. H models the sensor which measures the plant output y, and in general is a good approximation to the plant output, y. Noise n, which is not correlated to y, is added to the measurement Hy.
KeywordsPlant Output Plant Input Infinite Time Interval Linear Time Invariant Nonlinear Plant
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