Tuning of PID Controllers for Networked Control Systems

As the use of computer networks grows rapidly, applications, such as networked control systems (NCS), have emerged. NCS suffer from varying time-delays that bring new problems to the control loop. This paper discusses tuning of a discrete-time PID controller for NCS. A discrete-time PID controller is selected as a controller, because it is widely used in industry. Minimising of a cost function is a powerful tool in control design. Here the optimisation technique is used to find the best parameters of a PID controller, when the system has time-varying or stochastic delays. The cost variance is used as a robustness measure of the tuning. Comparisons to the Ziegler-Nichols and IMC tuning methods are given in a case where the process and the controller are distributed over the Internet. The tunings done in simulations are further verified on a real process. Despite of the simplicity of the PID controller adequate performance is still achieved and it is shown that the optimisation tuning is robust in the presence of a varying time-delay