This work presents an observer design methodology which guarantees stability as well as bounds for performance for simultaneous state and parameter estimation for a certain class of nonlinear systems. The approach is based upon the idea that the unknown parameters can be treated as augmented states of the system and stability of the state and parameter estimator is guaranteed by application of a variation of Kharitonov's theorem. Certain performance criteria can also be met with the design approach via a change of coordinates followed by application of Kharitonov's theorem. The presented technique is illustrated with an example where simultaneous state and parameter estimation is performed.
Proceedings of the 2005 American Control Conference, Portland, pp. 3610-3615 (2005)