Browsing by Author "Morari, M."
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Item Design of Robust Digital Controllers and Sampling-Time Selection for SISO Systems.(1987) Zafiriou, E.; Morari, M.; ISRThe stability of a digital control system and its performance in terms of the continuous plant output are studied. A two-step controller design is proposed. In the first step, the assumption of no modelling error is made and a controller that combines properties of the algorithm that minimizes the sum of squared errors and a deadbeat-type algorithm is designed so that no intersample rippling appears. In the second step, a filter is designed so that appropriate conditions which guarantee robust stability and performance in the presence of model-plant mismatch are satisfied. The effect of the sampling time on the achievable performance and the robustness properties of the system is examined and the results are incorporated in a complete procedure for sampling-time selection and robust controller design. Finally, the procedure and some theoretical implications are illustrated with examples.Item Design of the IMC Filter by Using the Structured Singular Value Approach.(1987) Zafiriou, E.; Morari, M.; ISRThe Internal Model Control (IMC) structure has been widely recognized as very useful in clarifying the issues related to the mismatch between the model used for controller design and the actual process. The structure also gives rise to a two step controller synthesis procedure, of which the second step deals with the design of a low pass filter such that robustness with respect to model-plant mismatch is guaranteed. The Structured Singular Value (SSV) was introduced recently and it allowed the non-conservative quantification of the concept of robust performance. This paper deals with the design of the IMC filter by uaing the SSV and it demonstrates how this approach can be used with either an H{SUB 2^-} or an H{SUB INFINITY} optimal controller.Item Digital Controller Design for Multivariable Systems with Structural Closed-Loop Performance Specifications.(1988) Zafiriou, E.; Morari, M.; ISRThe problem of the direct design of the closed-loop transfer function matri'; is addressed for multivariable discrete systems. The limitations imposed by unstable zeros, time delays and the structure associated with these are quantified. A design procedure is formulated that provides the designer with quantitative measures for evaluating the tradeoffs between different closed-loop interaction structures and durations. The problem of intersample rippling is also considered. The procedure requires only linearalgebra operations, includes the eventual construction of the feedback controller in state space, and is presented in a way that allows its straightforward computer implementation.Item Digital Controller Design for Multivariable Systems with Structural Closed-Loop Performance Specifications.(1987) Zafiriou, E.; Morari, M.; ISRThe problem of the direct design of the closed-loop transfer function matrix is addressed for multivariable discrete systems. The limitations imposed by unstable zeros, time delays and the structure associated with these are quantified. A design procedure is formulated that provides the designer with quantitative measures for evaluating the tradeoffs between different closed-loop interaction structures and durations. The problem of intersample rippling is also considered. The procedure requires only linear algebra operations, includes the eventual construction of the feedback controller in state space and is presented in a way that allows its straightforward computer implementation.Item Digital Controllers for SISO Systems: A Review and a New Algorithm.(1987) Zafiriou, E.; Morari, M.; ISRSeveral digital control algorithms for linear single-input single-output systems are examined and the effect of the sampling period on their performance is analyzed in terms of rippling, overshoot and settling time. The problem is addressed in the frequency domain (ztransform) and it is shown that each controller works for some classes of systems but that none works for all. The similarities and differences of these controllers are established and an explanation of their deficiencies is given based on the location of the zeros of the discrete system. The insight gained leads to a simple new rule for the design of a controller which combines the advantages of the different algorithms but at the same time is free of their problems. A single tuning parameter is included which directly affects the closed-loop speed of response and bandwidth. The parameter can be used to detune the controller in the event that the real system differs from the model on which the controller design is based. No tuning is necessary when the available model is exact, unless smaller values for the manipulated variable, at the cost of a slower response, are preferred.Item Internal Model Control: Robust Digital Controller Synthesis for Multivariable Open-Loop Stable or Unstable Processes(1990) Zafiriou, E.; Morari, M.; ISRThe two-step Internal Model Control (IMC) procedure is presented for the synthesis of multivariable discrete controllers. This paper adds the following features to the IMC design methodology: (i) Extension to open-loop unstable plants. (ii) Design of the first-step (no model error) IMC controller so that the L2-error (sum of squared errors) is minimized for every setpoint or disturbance vector in a designer-specified set and their linear combinations. (iii) The second-step (model-plant mismatch) multivariable low-pass filter is designed for robust stability and performance by minimizing a non-conservative robustness measure, the Structured Singular Value. (iv) The potential problem in intersample rippling is avoided by introducing a modification in the first-step controller and formulating the robust performance objective for the continuous plant output.Item Internal Model Control: Robust Digital Controller Synthesis for Multivariable Open-Loop Stable or Unstable Systems.(1987) Zafiriou, E.; Morari, M.; ISRThe two-step Internal Model Control procedure is used for the synthesis of multivariable discrete controllers for open-loop stable or unstable plants. The plant models used in the proposed method are transfer function matrices. In the first step the controller is designed so that the L{SUB 2^-}error (sum of squared errors) is minimized for every setpoint or disturbance vector in a set and their linear combinations. A modification is then introduced to avoid the potential problem of intersample rippling. In the second step a low-pass filter is designed so that stability and good performance characteristics are maintained in the presence of model-plant mismatch. The continuous plant output is considered in order to avoid bad intersample behavior. The filter parameters are obtained as the result of a minimization of a non-conservative robustness measure, the Structured Singular Value. Special filter structures have to be used for open-loop unstable or ill-conditioned plants.Item Robust H{SUB 2^-}Type IMC Controller Design via The Structured Singular Value.(1987) Zafiriou, E.; Morari, M.; ISRThe two-step Internal Model Control procedure is used for the synthesis of robust controllers for multivariable open-loop stable or unstable plants. In the first step the controller is designed so that the Integral Squared Error (ISE) is minimized for every external input (setpoint or output disturbance) direction in a set and their linear combinations. In the second step a low-pass filter is designed so that stability and good performance characteristics are maintained in the presence of model-plant mismatch. The problem is formulated as a minimization of the Structured Singular Value (SSV) for robust performance over the filter parameters.Item Setpoint Tracking vs. Disturbance Rejection for Stable and Unstable Processes.(1987) Zafiriou, E.; Morari, M.; ISRThe issue of controller tuning for setpoint tracking versus disturbance rejection has been discussed in the process control literature for many years. The purpose of this paper is to review and explain the problem and to point out solution procedures. We do not make any claims about developing anything novel. We merely summarize what is available at different places in the literature and put it in perspective in a tutorial manner.