Control of nonlinear systems using iterative feedback tuning

Iterative feedback tuning (IFT) is a tuning method based on minimizing some control criterion directly from experimental data. The method was originally developed for linear time-invariant systems, but many successful applications to nonlinear system have been reported in the literature. The contribution of this paper is to provide a preliminary analysis of IFT for nonlinear systems. This analysis sheds some light on the question of which nonlinear systems IFT may be expected to work for and also gives some guidance on how to choose the user's design variables for nonlinear problems. The discussions are backed up by simulations as well as an application to a DC-servo with backlash which initially exhibits a limit cycle.