H_∞ design to generalize internal model control

The internal model control (IMC) design method for stable plants has enjoyed much popularity due to its simple yet effective procedure. However, there are some shortcomings and inadequacies with the IMC design method for both stable and unstable plants which will be exposed in this paper. We propose a new H_∞ control design method that somehow captures the useful properties of the IMC design method but can be used for both stable or unstable plants (LTI, SISO) in a coherent framework. Moreover, some restrictive assumptions on the plant are relaxed and some of the IMC shortcomings and limitations are tackled.