Eliminating the DC component in steady state tracking error for unknown nonlinear systems: a combination of fuzzy logic and a PI outer loop

This paper presents a novel real-time control approach for a class of nonlinear unknown systems. The system is assumed to be represented by an affine model where all the involved nonlinear functions are online estimated by fuzzy logic units. Using these online estimations, an adaptive nonlinear control algorithm is established which consists two loops, the inner loop and outer loop. The inner loop is used to compensate the unknown nonlinearities whilst the outer loop is utilised to eliminate the DC component in the tracking error for the closed loop system. A real application to a pH control process in paper making has been made and desired results have been obtained