PID Controller with Effective Integral Control Ensures Robustness against Bounded Uncertainties

Modern industrial processes are increasingly gaining complexities as they are coupled-MIMO and nonlinear in nature, thus use of nonlinear MIMO controllers is unavoidable. However keeping in view better robust properties of PID controller it is preferable to employ a hybrid solution, which should be composed of PID and modern controller designs. Feedback linearization (FL) is one of such methods which give solutions to diffeomorphic nonlinear industrial control problems. input-output exact linearization (IOEL) cancels-out all the nonlinearities of plant by nonlinear feedback-controller, whereas a fixed structure linear controller, in outer loop, keeps the plant at required equilibrium position in state-space. In this study PID controller as preferable candidate for the outer loop design is investigated. It was found that, albeit, PID controllers are more robust then LQR design (thus it is a preferable choice), it does not always ensure robustness until-and-unless the loop should contain an effective-integral-control action