A robust nonlinear feedback control approach for the two-inertia servo drive systems

In this paper, a robust version of 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 treat the unknown disturbance as an extended state variable to be augmented with the plant model, and then design an extended state observer to estimate both the states and the disturbance, and a disturbance compensation mechanism is incorporated into the framework of the original CNF control, so as to alleviate the steady state bias due to disturbances, while retaining the fast transient performance of the CNF control. There is no explicit integration action introduced in this method, thus the headache of integrator windup will not occur. The new control method is then applied to design a two-inertia servo drive system. Simulation studies are conducted to verify that this control method can achieve good transient performance and steady-state accuracy in set-point tracking and is more robust to amplitude variations of disturbance/set-point.