Model reference control in two degree of freedom control systems: adaptive min-max approach

The design of a control system, that provides a model reference performance specification for the command response and, at the same time, achieves some prespecified feedback properties, is discussed. The use of a particular configuration of a two degree-of freedom controller allows the feedback and performance specifications to be tackled independently through the design of a feedback controller for the nominal plant and the model reference part by means of model matching in a min-max sense. A closed-form solution is provided for the optimal min-max controller. This closed-form solution will be very useful when using this controller in an adaptive way. The resulting adaptive controller consists of a fixed feedback part and an adaptive open-loop part. Only one degree-of-freedom is adapted. An example shows that it is possible to match the model reference performance specification, even near the stability limit