Dr. Xinggang Yan2024-12-102024-12-10https://dspace.academy.edu.ly/handle/123456789/762• Arobust observer is designed for nonlinear interconnected systems with uncertain ties where both the nominal isolated subsystems and interconnections are nonlinear. Anovelvariable structure dynamic system is designed to estimate the state variables of the interconnected systems asymptotically. • Sliding mode techniques have been utilised to design observers for a class of inter connected systems with both structured and unstructured uncertainties. For struc tured uncertainties, a robust sliding mode observer is designed using the distribution matrix of the uncertainties to guarantee that the error dynamics are asymptotically stable. For unstructured uncertainties, an ultimately bounded approximate observer is proposed to estimate the system states. • In the case that the interconnected systems have unknown time varying parame ters, adaptive observers are developed to estimate both the system states and the unknown time varying parameters simultaneously. A variable structure control technique is utilized to guarantee that the corresponding error dynamical system is convergent asymptotically while the parameter estimation error is uniformly ulti mately bounded. Moreover, adaptive sliding mode observer is proposed to estimate the inaccessible states in presence of unknown time varying parameters.ABSTRACT Some control design schemes need system states to develop controllers. In real applica tions, it might not be possible to measure all system states due to the cost of sensors or any technical issues. Therefore, Observers are needed to estimate unavailable states and then use the estimated states in control design schemes. This thesis focuses on the development of robust observers for nonlinear large-scale interconnected systems. System structures of nonlinear interconnected systems have been considered in the design to reduce conservatism and different techniques have been utilised in observer design to enhance the robustness. The main developments in this thesis include:sion system are employed to explain the designed observation scheme and to demonstrate that the designed adaptive observers can be applied to practical systems effectively.