Theory and design of robust direct and indirect adaptive-control schemes

A general approach for designing and the theory for analysing robust direct and indirect adaptive-control schemes for continuous-time plants is presented. The design approach involves the development of a general robust adaptive law and the use of the certainty equivalence principle to combine it with robust model reference and pole placement control structures. The global stability properties and robustness of the developed adaptive control schemes are established by using a general theory which relates the properties of signals in the mean sense over intervals of time. The developed theory and design approach are used to analyse and compare the robustness properties and performance of a wide class of robust adaptive laws which employ a dead-zone, fixed-σ, ε1, and a switching-σ modification as well as their variations.