摘要:

In quantitative feedback theory, plant parameter and disturbance uncertainty are the reasons for using feedback. They are defined by means of a setQ= {P} of plant operators and a setD= {D} of disturbances. The desired system performance is defined by sets of acceptable outputsAuin response to an inputu, to be achieved for allP∈Q. If any design freedom remains in the achievement of the design specifications, it is used to minimise the effect of sensor noise at the plant input. Rigorous, exact quantitative synthesis theories have been established to a fair extent for highly uncertain linear, nonlinear and time-varying single-input single-output, single-loop and some multiple-loop structures; also for multiple-input multiple-output plants with output feedback and with internal variable feedback, both linear and nonlinear. There have been many design examples vindicating the theory. Frequency-response methods have been found to be especially useful and transparent, enabling the designer to see the trade-off between conflicting design factors. The key tool in dealing with uncertain nonlinear and multiple-input multiple-output plants is their conversion into equivalent uncertain linear time-invariant single-input single-output plants. Schauder's fixed-point theorem justifies the equivalence. Modern control theory, in particular singular-value theory, is examined and judged to be comparatively inadequate for dealing with plant parameter uncertainties.

DOI:10.1049/ip-d.1982.0050

出版商:IEE    

年代:1982

数据来源: IET

摘要:

During a manoeuvre it is frequently found that a ship's yaw dynamics vary widely. To obtain a consistent response to the helm, it is therefore advisable to provide an autopilot to cope with plant uncertainties. Using the method of Horowitz, a high-loop-gain linear system may be designed which achieves an acceptable spread of transient responses. Unfortunately, there is a penalty to be paid in the form of excessive rudder activity when course keeping. It is therefore desirable to find a way of reducing the loop-gain requirement by attempting to remove some of the plant ignorance. The paper therefore proposes to reduce the plant uncertainty by using an inverse nonlinear compensator derived from a simple linear time-invariant model of the ship. It is then possible to control the resultant modified (and of reduced ignorance) plant with a much smaller loop gain. The paper shows that the design results in consistent manoeuvring performance coupled with much reduced rudder activity during course keeping. The complete compensator is readily realisable in DDC.

DOI:10.1049/ip-d.1982.0051

出版商:IEE    

年代:1982

数据来源: IET

摘要:

In the paper, the use of principal gains and phases in assessing the robustness of the closed-loop stability property is examined. An improved version of the recently developed principal gain-phase method is presented, and conditions are derived under which the technique is insensitive to small perturbations.

DOI:10.1049/ip-d.1982.0052

出版商:IEE    

年代:1982

数据来源: IET

摘要:

The paper introduces a general approach for analysing linear systems with structured uncertainty based on a new generalised spectral theory for matrices. The results of the paper naturally extend techniques based on singular values and eliminate their most serious difficulties.

DOI:10.1049/ip-d.1982.0053

出版商:IEE    

年代:1982

数据来源: IET

摘要:

For diagonally perturbed linear time-invariant multivariable feedback systems, the problem of finding an improved characterisation of the stability margin is examined. A readily computable lower bound for diagonally perturbed systems is developed using Perron-Frobenius non-negative matrix results. The present theory improves upon the existing singular-value stability-margin theory, providing a simple constructive method for determining previously unspecified norm weighting parameters (i.e. scaling factors) so as to minimise the conservativeness of stability-margin bounds.

DOI:10.1049/ip-d.1982.0054

出版商:IEE    

年代:1982

数据来源: IET

摘要:

A simple guide to specifying the bandwidth of an optimal control feedback system (as measured by the unity-loop-gain crossover frequency) is developed. A brief description is given of how the guide helps in the design of robust optimally controlled systems. The only information necessary to use the guide is an open-loop gain plot for the plant, thus providing the designer with a powerful design tool, independent of the method used for solving the optimisation problem.

DOI:10.1049/ip-d.1982.0055

出版商:IEE    

年代:1982

数据来源: IET

摘要:

A technique is described for the design of linear multivariable systems in which the plant parameters are constant but unknown. These parameters are represented by random variables with known mean values and variances. A Wiener type of z-domain solution is derived to the resulting generalised linear quadratic optimal control problem. These results are also interpreted in the time domain, and the equivalent Kalman filtering solution is derived. To enable the controller to be applied in self-tuning control systems, the plant is represented in discrete polynomial form and a simple diophantine equation solution is also obtained.

DOI:10.1049/ip-d.1982.0056

出版商:IEE    

年代:1982

数据来源: IET

摘要:

Discrete-time systems with uncertainty are considered. The system description is given in terms of a basic state-space model, which is then extended by the use of inequalities. This approach enables the assessment of performance deterioration due to uncertainty and leads to a design of control system with a given degree of risk. Possible applications of the results to the case of discrete-stage systems are discussed.

DOI:10.1049/ip-d.1982.0057

出版商:IEE    

年代:1982

数据来源: IET

摘要:

A procedure is developed for maximising frequency-weighted stability-margin singular values for a multivariable linear time-invariant feedback control system subject to design constraints requiring decoupling and asymptotic tracking in the presence of unstable command and disturbance signals and closed-loop stability. The results are derived using Sarason'sH∞optimal interpolation results, together with a new multivariable realisability lemma.

DOI:10.1049/ip-d.1982.0058

出版商:IEE    

年代:1982

数据来源: IET

摘要:

A robust control strategy for a linear sampled-data control system such that the error is asymptotically zero not only at, but also between, the sampling instances, in spite of both continuous and discrete disturbances, is proposed. The tracking and the disturbances are assumed to satisfy a linear autonomous differential-difference equation. The control strategy consists of an analogue servocompensator driving the process, a digital servocompensator driven by the tracking error and driving the analogue servocompensator, and a digital stabilising compensator regulating an overall augmented discrete system formed by the discretised process and both the digital and analogue servocompensators. The analogue servocompensator contains the modes of the reference and the disturbance signals; the digital servocompensator contains the modes of the discrete reference and discretised disturbance signals. The tracking error is shown to be asymptotically zero at all times. Also, the control input to the analogue servocompensator is zero in the steady state. If the exogenous signal mode is at the origin, the analogue servocompensator need not contain a simple mode at the origin. However, in this case the control input to the analogue servocompensator is a constant signal in the steady state.

DOI:10.1049/ip-d.1982.0059

出版商:IEE    

年代:1982

数据来源: IET