Minimally invasive control loop performance evaluation

Nowadays, companies are facing a strong pressure for industrial plant and machine optimization in order to achieve energy and material savings and increase product quality. Control loop performance assessment techniques create one cornerstone of this challenge. In process control applications, the performance is frequently compared just to the minimum variance controller. It is known that when optimizing process controllers having fixed structure (e.g. PIDs) different concepts must be applied. In authors recent work, the systematic approach for a class of fractional-order processes was presented. The method uses only a limited a priori information about the process. The performance index is defined as a difference between reference and actual sensitivity function at selected frequencies. In this paper, a minimally invasive method for performance index estimation is proposed. It employs running discrete Fourier transform. Next, the paper discusses various practical aspects and verifies the method on real temperature process.