Robust Control of Wiener Systems: A Case Study

The robustness of a typical control scheme for Wiener systems is analyzed. Wiener systems consist of the cascade connection of a linear time invariant system and a static nonlinearity. Several approaches were reported in the literature in order to control this kind of systems. Most of these control schemes involve a transformation of the measured variable as well as the setpoint by using the inverse of the nonlinear gain. As regards the uncertainty in the Wiener model, it is usually described as a partitioned problem. The linear block is considered as a parameter-affine-dependent model. On the other hand, the nonlinear block uncertainty is analyzed as a conic-sector. The robustness evaluation is performed using mu-theory. The results are interpreted on the basis of a simulation of a pH neutralization process