Stability of Cascaded Takagi-Sugeno Fuzzy Systems

A large class of nonlinear systems can be well approximated by Takagi-Sugeno (TS) fuzzy models, with local models often chosen linear or affine. It is well-known that the stability of these local models does not ensure the stability of the overall fuzzy system. Therefore, several stability conditions have been developed for TS fuzzy systems. We study a special class of nonlinear dynamic systems, that can be decomposed into cascaded subsystems. These subsystems are represented as TS fuzzy models. We analyze the stability of the overall TS system based on the stability of the subsystems. For a general nonlinear, cascaded system, global asymptotic stability of the individual subsystems is not sufficient for the stability of the cascade. However, for the case of TS fuzzy systems, we prove that the stability of the subsystems implies the stability of the overall system. The main benefit of this approach is that it relaxes the conditions imposed when the system is globally analyzed, therefore solving some of the feasibility problems. Another benefit is, that by using this approach, the dimension of the associated linear matrix inequality (LMI) problem can be reduced. Applications of such cascaded systems include multi-agent systems, distributed process control and hierarchical large-scale systems.