Iterative feedback tuning (IFT) enables the data-driven tuning of controller parameters without the explicit need for a parametric model. It is known, however, that IFT can lead to nonrobust solutions. The aim of this paper is to develop an IFT approach with robustness constraints. A constrained IFT problem is formulated that is solved by introducing a penalty function. Essentially, the gradient estimates decompose into: 1) the well-known IFT gradients and 2) the gradients with respect to this penalty function. The latter are obtained through a nonparametric model of the controlled system. This guarantees robust stability while only requiring a nonparametric model. The experimental results obtained from the motion control systems of an industrial wafer scanner confirm enhanced performance with guaranteed robustness estimates.
Heertjes, M. F., Velden, van der, B. J. C. H., & Oomen, T. A. E. (2016). Constrained iterative feedback tuning for robust control of a wafer stage system. IEEE Transactions on Control Systems Technology, 24(1), 56-66. https://doi.org/10.1109/TCST.2015.2418311