Plant-robust and controller-robust discrete-time PID design

In this paper, we present a method to design a digital PID controller that is robust with respect to perturbation in the plant (plant-robust) and the controller (controller-robust). The method parallels an earlier approach developed for the continuous-time case and makes judicious use of an orthogonal transformation. The resulting controller maintains stability under simultaneous coefficient perturbations in the plant and the controller. Moreover, the controller can be designed to leave maximal room for tuning the controller parameters.