Disturbance effects in nonlinear control systems and feedforward control strategy

This work concerns the development of a feedforward control strategy for measurable disturbance rejection in general nonlinear systems with feedback control. In other words, a separate design of disturbance feedforward controller is carried out to be augmented to an existing nonlinear feedback control system. With reference to a well known disturbance feedforward control of linear systems, feedforward control problem for general nonlinear control systems is formulated. The notion of disturbance effect is introduced with the aid of Lyapunov stability analysis of an asymptotically stable disturbance free nonlinear system with feedback control. With the establishment of the disturbance effect description, a feedforward control scheme that guarantees asymptotic stability in the presence of external disturbance is proposed and verified using the inverted pendulum system as an illustrative example.