IJCAS

With the increasing demands on system performance and reliability in engineering practice, fault tolerant control and disturbance rejection control are widely concerned by researchers, in which state and unknown input observation is the fundamental segment. Extended state observer (ESO) and disturbance observer (DO) are two mainstream tools in this field. However, lower triangle system structure is required in ESO design, and the application of DO relies on state measurement. In this paper, a robust composite observer is proposed to estimate states and faults simultaneously for one-sided Lipschitz uncertain nonlinear systems. At first, fault signal is split to matched and mismatched parts. Secondly, extended nonlinear unknown input observer (ENUIO) is designed to estimate system states and mismatched faults. Based on above estimated information, nonlinear disturbance observer (NDO) is utilized to reconstruct the matched faults. Then, synthesis condition derivation and rigorous stability analysis are conducted with the help of one-sided Lipschitz and quadratically inner-bounded conditions. Finally, two numerical examples are given to illustrate the validity and effectiveness of the proposed method.

Keywords: Multiple faults reconstruction, nonlinear disturbance observer, one-sided Lipschitz nonlinear system, unknown input observer.