Reduced-order observer design with unknown input for fractional order descriptor nonlinear systems

This paper investigates the observer design issues for the quadratic inner-bounded nonlinear descriptor fractional order systems. Considering the disturbances or inaccessible partial inputs, the order reduction of observer with unknown input is firstly implemented for effectively estimating the system state vectors. Then, for the purpose of the system conservatism reduction, the matrix F perpendicular to and the matrix generalized inverse technique are applied to design the reduced-order observer, which can deal with unknown input with less restrictions of coefficient matrices. By using fractional order Lyapunov direct method, sufficient conditions can be obtained to ensure the existence of the designed observer. Finally, a fractional order electrical circuit is applied to demonstrate the applicability of the proposed approach.