Variable universe fuzzy control of once-through steam generator feedwater

The feedwater control of once-through steam generators (OTSGs) is critical to the safety and stability of nuclear power plants. As traditional PID control methods are difficult to ensure good control of OTSGs under flexible operating conditions, a variable universe fuzzy control (VUFC) method is proposed for OTSG feedwater. The widely-used cascade control structure was first adopted for the OTSG feedwater control system. Then the outer-loop pressure and inner-loop feedwater controllers were designed as fuzzy controllers with their fuzzy universes adjusted adaptively during plant operations. To assess the performance of the VUFC method, dynamic responses of an OTSG employing the fuzzy controllers were compared with those adopting the well-designed PID controllers under typical load change transients. Comparison results illustrate that the VUFC method can provide much better OTSG pressure control with smaller overshoots and shorter settling times, demonstrating the applicability of the VUFC method for OTSGs to provide excellent feedwater control.