On Fractional PI Controllers: Some Tuning Rules for Robustness to Plant Uncertainties

The objective of this work is to find out optimum settings for a fractional PI controller in order to fulfil three different robustness specifications of design for the compensated system, taking advantage of the fractional order, λ. Since this fractional controller has one parameter more than the conventional PI controller, one more specification can be fulfilled, improving the performance of the system and making it more robust to plant uncertainties, such as gain and time constant changes. For the tuning of the controller, an iterative optimization method has been used based on a nonlinear parametric minimization routine. Two real life examples of application are presented and simulation results are presented to illustrate the effectiveness of this kind of unconventional controllers.