Decentralised variable structure observation of nonlinear interconnected systems with time delay

Decentralised local variable structure observers are proposed for a class of nonlinear interconnected systems in which the system states experience time delay while the inputs and outputs are delay free. The interconnections are nonlinear, unknown and time delayed, which provides particular challenge for the case of decentralised observation. It is not required that the bounds on the uncertainties in the isolated subsystems are functions of the system outputs. Unlike much of the existing work where the designed observer is an interconnected system, the observers designed in this paper are a set of decoupled dynamics and thus decentralised, which is more reliable in real implementation. A set of sufficient conditions are derived such that in the considered domain the corresponding error dynamics are asymptotically stable where the Lyapunov Razumikhin approach is employed to deal with the time delay. The delays are time varying, and there is no limitation on the rate of change of the time delays. A numerical example is presented to show the effectiveness of the results obtained.