DESIGN OF STABILITY-GUARANTEED FUZZY-LOGIC CONTROLLER FOR NUCLEAR STEAM-GENERATORS

A fuzzy logic controller (FLC) and a fuzzy logic filter (FLF), which h ave a special type of fuzzifier, inference engine, and defuzzifier, ar e applied to the water level control of a nuclear steam generator (S/G ). It is shown that arbitrary two-input, single-output linear controll ers can be adequately expressed by this FLC. A procedure to construct stability-guaranteed FLC rules Is proposed. It contains the following steps: 1) the stable sector of linear feedback gains is obtained from the suboptimal concept based on LQR theory and the Lyapunov's stabilit y criteria: 2) the stable sector of linear gains is mapped into two li near rule tables that are used as limits for the FLC rules; and 3) the construction of an FLC rule table is done by choosing certain rules t hat lie between these limits. This type of FLC guarantees asymptotic s tability of the control system. The FLF generates a feedforward signal of S/G feedwater from the steam flow measurement using a fuzzy concep t. Through computer simulation, it is found that the FLC with the FLF works better than a well-tuned PID controller with variable gains to r educe swell/shrink phenomena, especially for the water level deviation and abrupt steam flow disturbances that are typical in the existing p ower plants.