Analog simulation of a digital three-mode controller

Abstract

Textbook designs of digital systems are often based on classical responses produced by specific closed- loop transfer functions, and offer little assistance to the "analog" engineer who is required to convert a number of analog loops to digital control while maintaining product specifications. To ensure uni form operation of the plant during the conversion, it is desirable to have as little change as possible in the response of individual loops in order to minimize unexpected side effects. This paper describes a simulation procedure which enables the engineer to incorporate the familiar analog concepts of proportional, derivative, and integral modes into the digital software and to identify the mode coefficients with corresponding software variables. Thus the digital controller can be tailored to provide mode emphasis similar to that of the analog device being replaced. The whole sys tem, including the digital software, is simulated by analog means and the gain of each mode is adjusted independently until the desired response is obtained.