A nonlinear disturbance observer scheme for discrete time control systems

Abstract

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.

An enhanced bandwidth disturbance observer based control– S-filter approach

“…Further, the conclusions of the current paper are different from those of [30] in that the required bound for the 1-norm expressions are different. This work should therefore be viewed as a complementary work of [30] that guides the practicing engineers. This paper is organized as follows: The second section presents an expansion of the Q-filter and derives the governing equations according to variables defined within this new scheme.…”

“…Discrete time version of the same block structure requires g k 1 < 1/2 for stability. Here,g k represents the impulse response of the corresponding quantity in [30].…”

“…The framework considering the discrete time conditions is presented in [30]. The discrete time case of [30] assumes a saturation function, where a finite gain around zero is a necessity, whereas, the current paper considers a signum function leading to a totally different theorem and proof.…”

“…The framework considering the discrete time conditions is presented in [30]. The discrete time case of [30] assumes a saturation function, where a finite gain around zero is a necessity, whereas, the current paper considers a signum function leading to a totally different theorem and proof. Further, the conclusions of the current paper are different from those of [30] in that the required bound for the 1-norm expressions are different.…”

“…The discrete time case of [30] assumes a saturation function, where a finite gain around zero is a necessity, whereas, the current paper considers a signum function leading to a totally different theorem and proof. Further, the conclusions of the current paper are different from those of [30] in that the required bound for the 1-norm expressions are different. This work should therefore be viewed as a complementary work of [30] that guides the practicing engineers.…”