Composite tracking control of the nonlinear system with a partially unavailable state

The problem of composite tracking control is explored for a nonlinear system with partially unavailable state in this work. Specifically, the system states are categorised into available and unavailable states due to limitations in the sensor technology. Based on the perspective of the large-scale system theory, the nonlinear system is modelled as a composite of an available state subsystem (ASS) and an unavailable state subsystem (USS). To reduce system complexity and simplify the controller structure in the tracking control design process, a composite tracking control scheme (CTCS) is proposed, which combines the robust controller for ASS and multi-independent control input for USS. The robust controller is designed to manage the uncertain dynamics associated with the unknown vector function in ASS, while the multi-independent control input compensates for the uncertain dynamics of unavailable state. Compared with the existing methods, the proposed CTCS relies exclusively on available state variables, eliminating the need for estimated state from the observer. Finally, the effectiveness of CTCS is demonstrated by the velocity tracking of the quadrotor unmanned aerial vehicle simulation example.