Model-based piecewise affine variable-gain controller synthesis

In this paper, we introduce piecewise affine variable-gain controllers as a means to improve performance compared to linear controllers. Variable-gain controllers can improve upon the tradeoff between low-frequency tracking and sensitivity to high-frequency disturbances. However, performance-based tuning of the variable-gain controllers, is far from trivial. The piecewise affine control structure introduced in this paper allows to synthesize the shape of the variable-gain controller, by means of model-based optimization of a certain performance objective. Subsequently, this allows the controller design to be tuned for the disturbance situation at hand while optimizing performance. The proposed nonlinear performance-based controller synthesis strategy is applied to a model of a wafer stage of a wafer scanner.