Design and analysis of iterative learning controllers for uncertain systems

Abstract

This dissertation deals with iterative learning controller design for uncertain linear systems and analyzes properties of iterative learning control systems in the frequency domain. Firstly, we consider the problem of how to design an iterative learning controller when the controlled plant has uncertainty. Plant uncertainty is classified into two categories: unstructured uncertainty and parametric uncertainty. For each uncertainty modeling, we derive sufficient conditions for the iterative learning control system to converge despite the presence of the uncertainty. Based on the derived convergence condition, we show that the iterative learning controller design problem can be investigated from the viewpoint of robust controller design problem. Consequently, it is shown that the iterative learning controller that guarantees convergence for all admissible plant uncertainties can be designed by well-established robust control design techniques such as μ synthesis. In addition, we investigate convergence property of iterative learning control systems where the initial condition of the plant with respect to the iteration. Secondly, we look into iterative learning control systems for plants with rotation mechanism. In this kind of systems, we cannot make the initial state of the plant identical for every iteration, instead the initial state at each period is equal to the final state at the previous period. Using this property, we convert the iterative learning control system with a feedforward control input into a closed-loop system with another internal loop including a time-delay element. We analyze convergence of the iterative learning control system by examining stability condition of the resultant feedback control system and showed that the obtained stability condition is equal to the convergence condition of the iterative learning control system with invariant plant initial state. In addition, we investigate frequency domain properties of the feedback control...