Performance Comparison of PID Controller and H∞ Controller for integrating plus Time-delay process

Abstract

Time delays are common to many systems often caused by communication lag, material transport, delayed sensing etc. Time delay causes instability and generally, it is hard to control. In addition, integrating plus time delay process requires special care for stabilization. In this work, two design methods are adopted to achieve stability with good performance. In first case, a PID controller is designed for an integrating plus time delay process. A PID controller is known for its design simplicity, and it has universal acceptance in the industries. Because of simple understanding, the method is widely applicable to various processes having different dynamics. In this work, frequency response matching of actual and the desired closed loop systems at two low frequency points is used to design PID controller for integrating processes with delay. So, to design the PID controller for this process, two configurations are considered to get good set point response and load disturbance rejection. In first configuration, a double feedback loop is used where inner loop stabilizes the system by a gain, and the PID controller is placed in cascade before the inner loop to achieve desired set-point response and good load disturbance rejection. In the second configuration, a single loop is considered, and the PID controller is designed by considering a desired load disturbance rejection model of the system. In the second case, a model-matching H infinity controller is designed for the integrating process with delay for the same previous two configurations. Through simulation results, this work compares the performance of the above two controller with respect to set point tracking and load disturbance rejection. Also the value of ISE, IAE errors, gain margin, phase margin are calculated for the closed-loop systems with both the controllers.