A Modified IMC Structure to Independently Select Phase Margin and Gain Cross-over Frequency Criteria

Abstract

In this paper, a modified internal model control (IMC) is proposed to improve transient response by introducing an additional PD controller in the control loop of a first order plus time delay (FOPTD) system. The controller is tuned to satisfy phase margin (φm) and gain cross-over frequency (ωg) independently. In the proposed methodology, φm and ωg can be selected from a ωg - φm plane whereas basic IMC gives freedom to select φm and ωg from a ωg -φm line. Therefore, it improves the freedom for selection of these specifications by broadening the domain of selection from a line to a plane, also improving the overall response. Further the impact of the proposed controller is verified by considering transient parameters such as rise time (Tr), settling time (Ts) and maximum overshoot (%Mp) and the controller effectiveness is measured in terms of performance indices like integral square error (ISE), integral absolute error (IAE) and integral of the time weighted absolute error (ITAE).