Dynamic Controllers Which Use Difference Approximates of Output Derivatives and Their Practical Stability

Abstract

The derivative feedback is a classical but representative means in the design of control systems, and for practical reasons it is often replaced by its difference approximation. As the resulting closed-loop system involves a time-delay, it does not necessarily preserve stability however accurate the approximation is. Following the terminology of Palmor (1980), it may be said that the practical stability is not always guaranteed. The present paper studies the condition under which the practical stability is guaranteed for approximating output difference feedback controllers.