Patch theory: Robustness/performance enhancement of power plant pid control clusters through analytical design

In the previous work the PID cluster robustification has been carried out. It consisted in imparting some of the robustness/performance attainable by a full-order H_∞ robust controller onto the existing power plant PID control clusters through compensating for the main structural and/or dynamic deficiencies of the PID-based designs. For this purpose, augmentation of the existing PID clusters with several static and/or dynamic robustifying links extracted from the full-order robust controller, without fully implementing the latter, has been proposed. To permit easy disabling of the additional control elements, if needed, they were run in parallel with the existing PID based controls. The high order of robustifying links has been reduced for implementing on the existing DCS control blocks. However, the robustifying links extraction procedure was heuristic and involved a very time consuming exhaustive search with no guarantee of the desired outcome. In this paper, a new methodology for the design of robustifying links, referred to as "patch theory" is introduced. The methodology proposed replaces the heuristic search with the consistent analytical design with guaranteed outcome. Simulation example is presented to show the efficacy of the new approach.