A nonlinear disturbance observer scheme for discrete time control systems

This paper presents a modification to the original disturbance observer based control (DOBC) scheme by redefining the lowpass filter using a nonlinear element. The proposed technique improves the disturbance prediction performance for both small and large magnitude disturbance signals. The contribution of the current work is to unfold the stability and performance conditions under the proposed modification. A comparative set of simulation studies are discussed and it is seen that the proposed modification results in smaller disturbance prediction error energy and smaller tracking error energy when the plant model is discrete time and uncertain.