Random delay effect minimization on a hardware-in-the-loop networked control system using optimal fractional order PI controllers

Random delays have serious effects in networked control systems, which deteriorate the performance and may even cause instability of the system. Hence a controller which can make the plant stable at large values of delay is always desirable in NCS systems. Our previous work on OFOPI controller showed that fractional order PI controllers have larger jitter margin (maximum value of delay for which system is stable) for lag-dominated systems as compared to traditional PID controllers, whereas integer order PID controllers have larger jitter margin for delay-dominated systems. In this paper, a telepresence controller based on optimal fractional order proportional and integral (OFOPI) tuning rules is used to obtain the maximum value of delay (jitter margin) at which the system will be stable. To illustrate this, an extensive experimental study on the real-time Smart Wheel networked speed control system is performed using hardware-in-the-loop control. For this purpose, the real-time random delay in the world wide network is collected by pinging different locations, and is considered as the delay in our simulation and experimental systems. Comparisons are made with existing integer order PID controller. It is observed that the proposed OFOPI controller is a promising controller and has faster response time than the traditional integer order PID controllers. Also it is verified that since the plant into consideration viz. the Smart Wheel is a delay-dominated system, PID achieves larger jitter margin as compared to OFOPI tuning rules. Simulation results are presented to illustrate the effectiveness of the proposed OFOPI method.