Adaptive Observers With Persistency of Excitation for Synchronization of Chaotic Systems

We address the problem of master-slave synchronization of chaotic systems under parameter uncertainty and with partial measurements. Our approach is based on observer-design theory hence, we view the master dynamics as a system of differential equations with a state and a measurable output and we design an observer (tantamount to the slave system) which reconstructs the dynamic behavior of the master. The main technical condition that we impose is persistency of excitation (PE), a property well studied in the adaptive control literature. In the case of unknown parameters and partial measurements we show that synchronization is achievable in a practical sense, that is, with "small" error. We also illustrate our methods on particular examples of chaotic oscillators such as the Lorenz and the Lu oscillators. Theoretical proofs are provided based on recent results on stability theory for time-varying systems.