Systems Identification of a Cascade Controlled Servomechanism using Frequency Domain Analysis

Abstract

In this paper experiments aimed at identifying the systems parameters of a cascade-controlled servomechanism using both the time domain step  response method and frequency response domain Bode plot methods were investigated. In the cascade configuration, the velocity feedback  attenuator gain caused the response to become overdamped. Hence, the overdamped response made the step response systems identification  method inadequately as it requires at least an overshoot to correctly infer the systems transfer function. Nevertheless, using the frequency  response based Bode plot it was possible to parameterise the transfer function of the servomechanism. Furthermore, the obtained model of the  servomechanism, which was simulated in MATLAB, depicted the effect of varying the velocity feedback gain from 0.3 to 1 in both open and closed-  loop configurations. Finally, the output response of the transfer function for the experimental servomechanism which was obtained via the  frequency response method has been compared and validated against the experimental system’s output response Also, recent methods for systems  identification of transfer function parameters based on genetic algorithm and particle swarm optimisation have been compared. The  output of the transfer function model obtained via the frequency response-based method is in good agreement with the output response of the  experimental servomechanisms. Hence, this validates the frequency response-based method.