Recent research in the area of describing function approaches (both random-input and sinusoidal-input) has laid the foundation for a systematic approach to designing controllers for nonlinear plants. This paper provides an overview of one school of thought in this area, typified by the following key ideas: 1. Quasilinear models of the nonlinear system that account for the operating range of system variables must be more realistic than conventional linear models. 2. A staged design approach that applies more power to "difficult" nonlinear plants than to "easy" ones is more sensible than a single design method. 3. The designer should be led to a nonlinear controller design if and only if it is really required. These points will be developed, illustrated and justified in this presentation.

A Systematic Nonlinear Controller Design Approach based on Quasilinear System Models

Load–frequency control of interconnected power system with governor backlash nonlinearities

The paper is concerned with recent developments in the application of harmonic approximants to predict limit-cycling conditions in multivariable feedback systems. Emphasis is placed on computational procedures giving graphical interpretations in the frequency domain which will be useful in the subsequent design of suitable linear compensator elements. Early work based on the single-harmonic approximant is reviewed, and it is shown how this can be subsequently extended and refined to generate more accurate solutions based on higher-order-harmonic approximants. Some of the numerical problems involved are described, and solutions are proposed which make efficient use of the computational effort available. An example is given which allows results obtained from the various methods described to be directly compared.

Prediction of limit cycles in multivariable nonlinear systems

Computer-aided control system design , Computer-aided control system design , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

Computer-Aided Control System Design

analytical design of control systems, in which the numerous graphical techniques employed are suited to automated computation using modern interactive graphical procedures. Such procedures are particularly relevant in the study of nonlinear systems in which, inevitably, the computational process can be protracted. This paper describes a set of computer-based methods which are applicable to the study of a limited class of nonlinear feedback configurations in which the nonlinearities exist as separable bounded elements in an otherwise linear system. The approach is based on the

J. O. Gray

Papers

Paper: Computer aided design of multivariable nonlinear control systems using frequency domain techniques