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Digital Conversion of Nonlinear Compensators with Antireset-Windup Compensation: Studies, Analysis and Design

Abstract
All physically realizable systems are subject to saturations of one form or another. Control systems having saturations are susceptible to the nonlinear problem of reset-windup if the controllers within those systems contain one or more integrators. Reset-windup is a condition whereby the integrator continues to integrate the feedback error and add to the control signal, even in the presence of a decreasing error signal. This phenomenon can lead to excessive overshoot in the system in response to large setpoint changes. This paper discusses the problem of reset-windup in detail and presents several methods for correcting this problem in continuous-time systems as discussed in existing controls literature. Two approaches to the elimination of reset-windup are discussed in detail: the conventional anti-reset windup (CAW) scheme and the override signal (OS) scheme. The application of these methods to continuous-time systems is reviewed for simple example systems. The paper then proposes implementations of these methods for discrete-time systems, discusses problems associated with these implementations, including the phenomenon of "chatter", and presents design criteria to make these implementations useful. Finally, the practical application of antireset-windup compensation is discussed through the design of a digital controller for an existing system.
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Date
1992
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