A Decoupled Complementary Design Framework for Robust Tracking Control

Robust tracking control for unstable or non-minimum phase systems with unknown disturbance and/or modeling uncertainty is well-known to be challenging. In this paper, a new complementary design framework is proposed to achieve robust tracking control. The proposed controller consists of two parts: an inner loop control which stabilizes the plant while also conducting compensation of disturbance/uncertainty at the same time, and an outer loop nominal tracking control which can be designed with the existing methods based on the stabilized plant model without disturbance/uncertainty. The purpose of the inner loop compensation is, hence, to suppress the impacts of disturbance/uncertainty on the plant so that the nominal tracking performance could be recovered in an environment with unknown disturbance/uncertainty. Since the design of outer loop tracking control is conducted on the compensated plant model, the challenge is eliminated effectively for the robust tracking control of unstable or non-minimum phase plants. Simulations are presented to show the superior tracking performance with much improved robustness.