Individual Channel Design Research Articles

The role of single-loop subsystems in multivariable control by individual channel design of 2-input and 2-output systems

Individual channel design is an applications-oriented framework for the analysis and design of multivariable control systems (O'Reilly and Leithead 1991). Whilst most previous work focuses on the analysis of multivariable systems using individual channel design, this present paper concentrates on some design aspects for 2-input 2-output systems. Two basic issues are examined: first, the role of single-loop subsystems (as opposed to channels) in multivariable control by individual channel design; second, how single-loop subsystems facilitate an attractively simple sequential design procedure for channels of any bandwidth. This sequential individual channel design procedure is based on two interesting results. First, there exists a dynamic performance relationship between the individual channels and their associated single-loop subsystems in that the deviation of the single-loop subsystem sensitivity function from the associated channel sensitivity function is the same for both channels. Second, provided th...

M-Input m-output feedback control by individual channel design Part 1. Structural issues

A new applications-oriented approach—individual channel design (ICD)—to multivariable feedback control for 2-input 2-output systems was presented and justified in a series of papers (O'Reilly and Leithead 1991, Leithead and O'Reilly 1991 a, b, 1992 a). This paper is the first part of a two-part investigation into the extension of the ICD framework, and the performance issues thereof, to general m-input m-output systems. The main results of this first part are fourfold. First, the ICD framework for general m-input m-output systems is justified for all multivariable system structures (RHP poles and zeros). In particular, it is shown that ICD on the original m-input m-output cross-coupled multivariable system is valid irrespective of the degree of cross-coupling. Second, the influence of (individual transfer function, channel, transmission) right half-plane zeros on controller design and closed-loop channel performance is elucidated. Third, the existence of fixed stabilizing controllers for uncertain m-input...

The Direct (Inverse) Nyqulst Array and Quantitative Feedback Theory Approaches to Multivariable Feedback Design : A Structural Assessment for 2-Input 2-Output Systems

A new applications-oriented approach-Individual Channel Design - to multivariable feedback control was presented in O'Reilly and Leithead (1991) and Leithead and O 'Reilly (1991 a, 1992a, b).There it was shown that Individual Channel Design is a transparent.flexible and supportive design methodology which directly aims to meet the user's control requirements and is well-suited to the engineering context. This paper is addressed to the question as to what is the relationship of Individual Channel Design to earlier frequency-domain methods for multivariable design such as the Direct (Inverse) Nyquist Array (Rosenbrock 1969, 1974) and Quantitative Feedback Theory (QFT) (Horowitz 1991). More generally, given that Individual Channel Design is a framework for the evaluation of any linear time-invariant muJtivariable controller, this paper provides an interpretation and assessment of these two important frequency-domain methods; it highlights their advantages and establishes for what classes of multivariable problems they are valid. For ease of exposition, the investigation focuses on 2-input 2-output multivariable systems (O'Reilly and Leithead 1991): the conclusions extend, With the necessary changes, to general m-input m-output systems (Leithead and O'Reilly 1992c).

Performance issues in the individual channel desigm of 2-input 2-output systems Part 3. Non-diagonal control and related issues

A new applications-oriented approach—individual channel design (ICD)—to multivariable feedback control—was presented in an earlier paper (O'Reilly and Leithead 1991). This paper is the final part of a three-part investigation into the performance issues raised by ICD for 2-input 2-output strongly coupled multivariable systems. Parts 1 and 2 (Leithead and O'Reilly 1991, 1992 a) respectively show that fixed stabilizing controllers exist regardless of the structure of the multivariable system and that the use of phase and gain margins and SISO Nyquist-Bode loop shaping design is justified. The three-part series of papers also develops an analytic framework for investigating and understanding the potential and limitations of the feedback design of any linear time-invariant controller. The main results of this final part are threefold. First, restriction to diagonal feedback control in ICD (O'Reilly and Leithead 1991) or elsewhere is not a significant restriction on performance. Second, non-diagonal feedback c...

Performance issues in the individual channel design of 2-input 2-output systems. Part 2. Robustness issues

In this second part of a three part series of papers examining the performance issues raised by the introductory paper (O'Reilly and Leithead 1991) on individual channel design for multivariable control, attention is focused on robustness: that is, on the meeting of performance specifications—in particular closed-loop system stability—in the face of plant uncertainty. The main results are that the use of phase margins and gain margins to assess robustness of 2-input 2-output multi-variable systems is justified. Further, it is shown that controllers for uncertain 2-input 2-output multivariable systems can be designed by classical SISO Nyquist-Bode local loop shaping using stable minimum phase controllers. Several additional results are also described in the paper.

Multivariable control by ‘individual channel design’

Abstract A new approach—individual channel design (ICD)—to an enduring problem— multivariable feedback control—is presented. The approach is applications-oriented: it starts from the engineering premise that feedback control design is interactive; it involves an interplay between customer specification, uncertain plant characteristics, and the multivariable feedback design process itself. It is shown that individual signal transmission channels arise naturally from customer specification on selected plant outputs with no loss of structural (loop interaction) information. By invoking customer performance specification on different channels, highly successful single-input single-output classical (Nyquist-Bode) design is made possible. ICD is not a design method per se per se; rather it is a global structural framework wherein the possibilities and limitations for local-loop-shaping design (e.g. Bode or Nichols) of a particular plant are made apparent from the outset. Also, the conditions are established whereby channel gain and phase margins are robust measures of stability. In this way, a transparent, flexible and supportive design methodology is developed which directly aims to meet the users’ control requirements and is well-suited to the engineering context. An automotive gas turbine control case study illustrates the salient features of the processs of ICD.

Performance issues in the individual channel design of 2-input 2-output systems Part 1. Structural issues

Performance issues in the individual channel design of 2-input 2-output systems Part 1. Structural issues