OPERATOR CONTROL THEORY AND A NEW CLASS OF NONLINEAR CONTROLLERS.

An operator formalism is used to extend the Internal Model Control (IMC) design approach to nonlinear lumped parameter systems. It is proven that the attractive properties of IMC - as studied in linear control system design - carry over to the general nonlinear case: for open-loop stable systems the feedback controller can be designed like a feedforward controller: the structure of the nonlinear controller is determined by the physical system while the stability issue can be disregarded during the initial stages of the design procedure; robustness, i. e. stability in the presence of plant model mismatch, can be addressed directly. Simulation examples from chemical engineering demonstrate the simplicity of the design procedure, the excellent performance of IMC for nonlinear lumped parameter systems and show that IMC works well even in the case where no linear controller can yield stable behavior. These promising results are an incentive to solve some of the theoretical questions which had to be left unanswered and to pursue experimental testing of the scheme.