A design of switching supervisory control based on fuzzy-PID controllers for VVER-1000 pressurizer system with RELAP5 and MATLAB coupling

Abstract

The safe operation of Pressurized Water Reactors (PWRs) is highly dependent on the Pressurizer (PRZ) system to stabilize the primary coolant pressure fluctuations during normal operation and maintain the pressure within specified boundaries. The behavior of the PRZ system is inherently non-linear and time-variant. Thus, it may not appropriate and precise enough to model it by the use of transfer functions or linear time-invariant state-space forms. As far as the authors know, the RELAP5 thermal-hydraulic code is one of the best platforms to represent a best-estimate (realistic) model for the PRZ system so far. Although the RELAP5 is capable of modeling the PRZ as a non-linear, time-variant, and dynamic system in an unknown model structure, it only uses classic controllers such as PID and Lead-Lag. According to the above issue, the RELAP5 code and MATLAB software are coupled together in this paper to use the capabilities of both the MATLAB software (the ability to implement advanced controllers) and the RELAP5 code (providing an accurate thermal-hydraulic model for the PRZ system). Conclusively, this coupling provides a new platform for designing and utilizing various intelligent and advanced controllers for the PRZ system. Moreover, this paper fully presents a switching supervisory control based on Fuzzy-PID controllers (as a model-free and intelligent controller) for the VVER-1000 PRZ system to adjust both its pressure and level outputs. In this work, the PRZ is modeled as a Multi-Input Multi-Output (MIMO) system with consideration of the interactions between outputs (pressure and level). Eventually, the designed control system is used for several case studies. The results show the high performance of the presented control system for the VVER-1000 PRZ system that can be applied for other PRZ systems.