Design of Improved Fractional Filter Based IMC-PID Controller for SOPTD Process Using ISE Minimisation

This article concentrates on the design of PID based on a prominent IMC (Internal Model Control) scheme in combination with fractional filter to achieve control over a SOPTD (Second Order plus Time Delay) system, which is one among the most common type of system found in industrial applications. The structure of the controller consists of IMC based PID and an IMC filter which is fractional in nature. An optimum higher order fractional IMC filter structure is chosen and additionally Pade's procedure is incorporated for higher order approximation of time delay. The performance of the controller is determined by the IMC filter structure used for designing the controller. Here, the control parameter which include controller gains and coefficients of fractional filter are optimized using ISE (Integral Square Error) minimization. Simulations have been carried on a generic second order system with significant time delay with the help of Simulink model and math script developed for control parameter optimization. The performance of the control strategy with proposed control parameter values in tracking the set point is evaluated by comparing the obtained results with the existing conventional control schemes present in the literature, by comparing the standard performance metrics yielded through them. The robustness of the controller is also tested by analyzing its performance under the influence of disturbance and also the efficiency of the controller in tackling the measurement noise is also observed. Also, analysis is carried out on all the mentioned controllers to investigate the performance deterioration for uncertainties in the controller parameter. The proposed control parameters obtained using ISE minimization shows improved closed loop performance in terms of disturbance rejection and set point tracking.