Closed-loop pole: Difference between revisions

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In [[control theory]] there are two main methods of analyzing feedback systems: the [[transfer function]] (or frequency ___domain) method and the [[state space (controls)|state space]] method. When the the transfer function method is used, attention is focused on the locations in the [[s-plane]] where the transfer function becomes infinite (the '''poles''') or zero (the '''zeroes'''). Two different transfer functions are of interest to the designer. If the feedback loops in the system are opened (that is prevented from operating) one speaks of the '''open-loop transfer function''', while if the feedback loops are operating normally one speaks of the '''closed-loop transfer function'''. For more on the relationship between the two see [[root-locus]].

'''Closed-loop poles''' are the positions of the poles (or [[eigenvalues]]) of a closed-loop transfer function in the [[s-plane]]. The [[open-loop]] transfer function is equal to the product of all transfer function blocks in the [[forward path]] in the [[block diagram]]. The closed-loop transfer function is obtained by dividing the open-loop transfer function by the sum of one (1) and the product of all transfer function blocks throughout the [[feedback loop]]. The closed-loop transfer function may also be obtained by algebraic or block diagram manipulation. Once the closed-loop transfer function is obtained for the system, the closed-loop poles are obtained by solving the [[characteristic equation]]. The characteristic equation is nothing more than setting the denominator of the closed-loop transfer function to zero (0).