A novel robust tracking controller based on hierarchical perturbation compensation

A robust tracking controller for mechanical systems is proposed by combining a robust perturbation compensator with a nominal tracking controller designed in a sliding mode control (SMC) frame. Basically, the robustness of the system is achieved by the perturbation compensator and this approach enables a smooth sliding mode in the control loop tracking without chattering problem. A unified view is given to a class of perturbation observers and three kinds of expressions for the perturbation of a plant is described. In terms of the view and expressions, we propose the feedforward perturbation observer (FFPO), the feedback perturbation observer (FBPO), and the sliding mode perturbation observer (SMPO). Then, by hierarchically adopting these three observers, the hierarchical perturbation compensator (HPC) is constructed. The adaptive and integral property of the HPC greatly enhances the performance and stability robustness of the system with just the necessary amount of control effort. Through the stability analysis, it is shown that the HPC has an inherent property to overcome the limit of existing perturbation observers. The experimental results for a mechanical system demonstrate the effectiveness of the proposed controller