Cascade proportional integral retarded control of servodrives

Abstract

The goal of this work is to propose a new time-delay control law called the cascade proportional integral retarded controller, which is aimed at position control of DC servodrives. The proposed controller has a cascade inner loop-outer loop structure. The inner loop is endowed with an integral retarded algorithm, and regulates the servodrive angular velocity. A proportional controller closes the outer loop whose goal is to regulate the servodrive angular position. The tuning of the cascade proportional integral retarded controller is accomplished into two steps. In the first step, the velocity of the inner loop is tuned by assigning a triple dominant root. The second step tunes the outer position loop. It is also possible to modify the cascade proportional integral retarded controller to avoid velocity measurements without adding extra filters. Moreover, the cascade topology of the cascade proportional integral retarded controller makes it easy to introduce a nonlinear saturated gain in the outer loop. This controller termed as the cascade nonlinear proportional integral retarded controller prevents overshoots for large values of the set point, avoids excessive control effort, and maintains a prescribed value of the angular velocity. Experiments in real-time using a laboratory prototype allow assessing the performance of the proposed controllers.