Abstract In this paper, the distributed fault estimation problem of discrete-time nonlinear interconnected systems is studied. Unlike in continuous-time interconnected systems, the coupling terms between interconnected subsystems make the design of fault estimation observer for discrete-time interconnected systems more difficult. An augmented interconnected system is constructed, and the global error dynamical equation of interconnected systems is formed from a global perspective, which is convenient for handling the coupling terms. Furthermore, the unknown input observer-based distributed fault estimation design is proposed to completely decouple external disturbances, and a multi-constrained design is given to calculate the matrix gains of the fault estimation observer. The sufficient conditions of this design are presented in terms of linear matrix inequalities. Finally, simulation results of the tripled-inverted pendulum model are given to verify the effectiveness of the present design techniques.
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