Robust composite nonlinear feedback control with application to a servo positioning system

A new robust composite nonlinear feedback (CNF) control method is proposed to achieve fast and accurate set-point tracking for linear systems subject to input saturation and disturbances. The basic idea is to incorporate disturbance estimation and compensation into the framework of the original CNF control so as to eliminate the steady-state bias due to disturbances and retain the fast transient performance of the original CNF control. There is no additional integration action introduced in the new method, which is in contrast with the previous work, i.e., the enhanced CNF control. The new method is applied to design a control law for a dc servomotor positioning system. Simulation and experimental results show that the new method can achieve better transient performance and steady-state accuracy in set-point tracking and is more robust to amplitude variations of disturbance/set point compared to integration-based control.