Analysis On Stability Domain Of Two-Degree-of-Freedom Controller And Its Applications On Thermal Plant

Desired dynamic equation method (DDE) is a two-degree-of-freedombased tuning method for PI/PID controller, which establishes a relationshipbetween the parameters of the controller and the coeffients of the desireddynamic equation of the control system, so that makes the physical meaningof the parameters more explicit. A large number of studies on simulationexperiments and practical applications have demonstrated good performanceof this method, but seldom studies have been conducted to systematicallydiscuss the stability of the controller. It is no doubt that the confirming of thestability domain of the controller can deal with this problem. Otherwise, thecalculation for the stability domain also gives help to the optimization of thecontroller.In the first place, a new method modified from open-loop D-partition(OLDP) method was proposed to calculate the stability domain of thecontroller, which can specify not only the boundaries but also the inner areasof the stability domain at the same time. To illustrate the feasibility of the newmethod, several typical examples were cited, including first-order plant,second-order plant, high-order plant, and non-minimum phase plant, whichoften appear in thermal processes.In the second place, a calculation method was introduced to work out thestability domain of the DDE-PI and DDE-PID controller based on themodified OLDP method. Furthermore, according to the results of thecalculation, the characteristics of the stability domain were drawn out, whichalso provided a theoretical analysis and explanation of the stability of theDDE-PI/PID controller.In the last place, the digital electric-hydraulic control system (DEH) forsteam turbogenerator unit was cited as an application of the stability domainof the two-degree-of-freedom controller. By optimizing the parameters in the stability domain, a DDE-PI controller was designed to accomplish successfulcontrol of the system.