Robust loopshaping using iterative feedback tuning

Iterative Feedback Tuning (IFT) is a direct tuning method using closed loop experimental data. The method is based on numerical optimization and in each iteration an unbiased gradient estimate is used. In this contribution we show how to use IFT to do robust loopshaping. One method, based on the approach suggested by Glover and McFarlane [1], uses an approximate H_∞ cost function and alternates between updating the loop gains and the robustness margins. In a second, H₂ based method, a joint criterion of robustness and performance is optimized. The methods are illustrated on numerical examples.