Showing papers on "Robust control published in 1975"

Multivariable tuning regulators: The feedforward and robust control of a general servomechanism problem

Abstract: A new notion of compensator identification, as opposed to the conventional plant identification problem, is introduced in this paper. It is assumed that it is desired to synthesize a robust feedforward-feedback controller for an unknown plant so that asymptotic tracking, in the presence of disturbances, occurs. The only assumptions made regarding the description of the plant model are that 1) the plant is linear and time-invariant and 2) the uncontrolled plant is stable. Note that it is assumed that the order of the plant model is unknown. It is assumed that the control inputs to the plant can be excited, that the outputs of the plant which are desired to be regulated can be measured, and that the class of disturbance inputs and reference inputs is known. In addition, it is also assumed in the feedforward controller case, that the disturbance inputs can be measured and be excited; this assumption is not required in the robust feedback controller case. Necessary and sufficient conditions which allow the robust feedforward-feedback compensator to be synthesized so that the controlled system is stable and so that asymptotic tracking, in the presence of both measurable and unmeasurable disturbances, occurs are obtained. An algorithm which allows the controllers to be synthesized is given. Some numerical examples are included to illustrate the results.

The robust decentralized control of a general servomechanism problem

Abstract: The decentralized robust control of a completely general servomechanism problem is considered in this paper. Necessary and sufficient conditions, together with a characterization of all decentralized robust controllers which enables asymptotic tracking to occur, independent of disturbances in the plant and perturbations in the plant parameters and gains of the system, is obtained. A new type of compensator called a decentralized servo-compensator which is quite distinct from an observer is introduced. It is shown that this compensator, which corresponds to an integral controller in classical control theory, must be used in any decentralized servomechanism problem to assure that the controlled system is stablizable and achieves robust control; in particular, it is shown that a decentralized robust controller of a general servomechanism problem consists of two devices (i) a decentralized servo-compensator and (ii) a decentralized stabilizing compensator. It is then shown that, under certain mild conditions, there almost always is a solution to the robust decentralized servomechanism problem for any composite system consisting of a number of subsystems interconnected in any arbitrary manner. This last observation has important implications for process control.

An Inverse Optimal Control Problem and Its Application to the Choice of Performance Index for Economic Stabilization Policy

Abstract: The specification of a performance criterion is one of the basic requirements for the formal analysis of quantitative decision processes. A procedure of quantitatively selecting the performance index for economic stabilization policy by solving the so-called inverse optimal control problem is developed. When a closed-loop system with a known control policy is given, the inverse optimal control problem is to determine performance indices for which the given control rule is optimal. A sufficient condition is developed for the solution of the inverse problem for long-run economic stabilization policy, and an explicit solution is obtained for short-run economic stabilization policy by considering a special case where the performance index does not penalize the costs of implementing control policies. The solution of the inverse problem is found to be not unique in general, which implies that the optimal control policies are fairly robust against different performance indices. Also, it is found that the solution of the inverse problem for a linear regulator holds true for the linear tracking problem, which makes the analysis much simpler. A procedure is developed for the selection of the performance index along with the optimal feedback control policy by which the economic system is to reveal the desired characteristics. The procedure demonstrates the determination of the steady states as policy goals, the computation of the feedback control policy, and the construction of a performance index, through a small econometric model.