Analysis of Parallel Control Structure for Efficient Servo and Regulatory Actions

Abstract

This paper investigates an intriguing issue about the tuning aspects of the parallel control structures. This parallel control structure essentially decouples the servo action from the regulatory action and provides an opportunity to the control engineer for separately deciding the ability of the controllers for servo and regulatory action. This paper provides a thorough comparative study and thereby suggesting an appropriate combination of tuning rules for achieving better efficiency of the control structure. Three different well accepted tuning rules viz. Ziegler Nichols, Direct Synthesis (DS) and Gain Margin Phase Margin formulae have been considered and a critical analysis of the control tuning rules combinations have been performed. The performance of considered tuning rules combinations is assessed on the basis of a transient response criterion, i.e., overshoot, an error-based criterion, i.e., Integral of time-weighted absolute error for both setpoint and disturbance rejection, and a measure of controller output aggression, i.e., Integral of absolute rate of controller output. On the basis of performed studies for a first-order plus dead time system, it may be inferred that DS–DS tuning rule combination provided superior performance among all the considered cases for nominal as well as plant-model mismatch case.