Fixed-Time Disturbance Observer Design for Brunovsky Systems

This brief presents a fixed-time disturbance observer for Brunovsky systems. The proposed disturbance observer is composed of a uniform convergent part and a finite time convergent part. The uniform convergent part first drives the estimation error trajectories into a compact set containing the origin and then the finite time convergent part achieves exact disturbance estimation. The proposed disturbance observer can achieve exact disturbance estimation within finite time upper bounded by a constant independent of initial estimation error. In addition, the upper bound of the estimation time can be calculated theoretically. Numerical simulations are provided to demonstrate the effectiveness of the proposed disturbance observer and verify the declared fixed-time property.