Finite-time adaptive control based on fuzzy observers: Addressing unmeasured states and strict constraint conditions

For time-varying constraints in nonlinear systems with unmeasured states, a finite-time fuzzy tracking control strategy is constructed. A state observer based on fuzzy logic systems (FLS) is applied to not only approximate the unknown nonlinear functions, but also estimate the unmeasured states in the system. In numerous real-world facilities, state constraints are commonly encountered, which is a crucial factor resulting in system instability. In the construction of an adaptive controller, barrier Lyapunov functions (BLFs) are adopted to handle full-state constraints, and assure that every system state remains within the specified constraints. According to finite-time stability, the stability of the closed-loop system is assured, and the output is well driven to achieve the desired tracking effect in finite-time. Finally, the validity of this approach is proved by simulations of a direct-current (DC) motor system and a typical nonlinear system, the continuous stirred tank reactor (CSTR).