Dual parameterisation has recently been presented for the class of all stabilizing controllers for linear minimum phase rational plants. It is shown that the result can be extended to the parameterisation of all stabilising controllers for linear nonminimum phase rational plants. The parameterisation for nominal plants is a special case of the new parameterisation. Numerical examples are provided to illustrate the new parameterisation.

The authors discuss sufficient and necessary conditions guaranteeing the internal stability of systems. Counterexamples are constructed, and it is shown that conditions given by some current literature are not sufficient. The rigorous version is then given.

The Dahlin controller is studied in the complex-frequency domain in terms of performance and robust stability. Several well known digital control algorithms are compared with the Dahlin controller and found to be equivalent to it. The possibility of extending the Dahlin controller to the control of plants with zeros outside the unit circle and unstable plants is discussed. The essential cause of ringing is investigated and some ambiguous formulation is clarified. A new procedure is developed for digital controller design. Compared with conventional methods, it provides a more effective method of eliminating ringing. Finally, numerical examples are given to illustrate the new approach.

The existence of both right-half-plane poles and time delay makes it difficult to obtain a higher control quality. Recently, a modified Smith predictor for unstable processes with time delay was presented and good performance was obtained. In this paper, the modified Smith predictor is discussed. A modified structure is presented. The new one not only is simple for analysis and design but also avoids the improper element. Instead of introduction of an inner loop, a direct design procedure is given and analytical formulas for the controllers are provided. The time domain performance for both trajectory and regulatory responses is obtained quantitatively. Sufficient and necessary conditions for robust stability are also given. The new structure and design method can also be used for the control of integrating processes with time delay and stable processes with time delay. Numerical examples are provided to illustrate the proposed method.

In this paper, the Smith predictor, known as the dead-time compensator, is extended to the control of a class of nonminimum phase processes referred to as inverse-response processes. An analytical design procedure is developed based on modern H

Astrom et al. have proposed a new Smith predictor to control the process with an integrator and a long time delay. Though the method provides significant performance improvement, it fails to give effective tuning rules even when the integral constant is equal to 1. In this paper the method is extended to the general integrator/time delay process. A clearer and more logical design procedure is formulated, and simple tuning rules are developed. It shows that there is a minimum-order compensator for the process. Illustrative examples show the superiority of the proposed scheme in terms of both closed-loop performance and robustness.

In this note, the problem of minimal-order stabilization in the case where the plant is minimum phase is studied. A low bound on the order of stabilizers is derived and a set of minimal-order stabilizers are characterized. The low bound is related to the number and location of the plant’s unstable and lightly damped poles and the number of zeros. How to construct a minimal-order or low-order stabilizer for a general case is also discussed and the algorithm is provided. Numerical examples are given to illustrate the proposed method.

This paper presents a new PID controller design method for integrating processes with time delay and time constant. First, the conditions that guarantee the stability of closed-loop system are investigated. Then an optimization method using H∞ performance criterion is developed for deriving the controller. The stability and performance of closed-loop system are analyzed. The relationship between the closed-loop frequency response and the corresponding time-domain response is also examined. Examples are given to illustrate the proposed method. (1999 Elsevier Science Ltd. All rights reserved.

ln this paper, the conventional Smith predictor is modified, which leads to significant improvements in its regulatory capacities for reference inputs and disturbances. The proposed modification utilizes the existing prediction of the conventional time delay compensator and decouples the setpoint response from the disturbance response. The setpoint response and the disturbance response of the closed-loop system are adjusted by two parameters, respectively. This allows the designer to optimize them simultaneously. Illustrative examples are provided to show the advantages of the modified scheme.