Comparison of different techniques for nonlinear output feedback adaptive control

A number of techniques have been developed in the past for adaptive control of nonlinear systems using output feedback. These techniques have been compared from a number of viewpoints like the underlying class of nonlinear systems, the nature of the theoretical results (e.g., global versus semiglobal), and the issue of over-parameterization. One issue that has not received enough attention is how these different techniques compare when they can be applied to the same system. For example, the class of nonlinear systems in output feedback form, treated in the books by Krstic et al. (1995) and Marino and Tomei (1995), can also be treated by the high-gain observer method of Khalil (1996, 1997) and the H^∞ method of Tezcan and Basar (1999). We use simulation to compare the performance of different output feedback nonlinear adaptive controllers