Comparing 2DOF PI and DO-FPI controllers for the first-order plants

The paper compares a traditional two-degree-of-freedom PI controller (2DOF PI) with a disturbance observer based filtered PI control (DO FPI) with scalable filtering properties. Analytical tuning of both control loops is based on specifying position of their double real dominant poles. As in the papers [1], [2], a core structure of a filtered P controller (with adjustable filtering properties) is augmented to the DO FPI controller with an integral action based on an load (input) disturbance reconstruction using inversion of the plant dynamics. Thereby, the introduced filters may take arbitrary order by simultaneously keeping fixed position of the double dominant closed loop pole which enables noise attenuation adjustment without a necessity to repeat analysis of the optimal P controller tuning. This new simple modular approach is compared with the traditional 2DOF PI controller with an equally specified double real dominant pole. This one-parameter tuning procedures illustrated by an example of an optical plant control show possibilities of a significant increase of the closed loop performance by simultaneously remaining to be simple and transparent enough.