Simulation Study On Water Level Control Of Steam Generator

Steam generator (SG), an important heat exchanger that connects pressured water reactor's primary circuit with secondary circuit, is considered the intersection of primary circuit and secondary circuit. The main function of steam generator is transferring the heat from the reactor core carried by primary side coolant to secondary side water through U-tube, then secondary side water change into steam which is carried to the turbine. Water level has a direct effect on steam and the safety of steam generator. Therefore it is important and necessary for us to control water level of steam generator and it is valuable to have study on water level control.SG level control system, a kind of multi-input single-output system with the character of nonlinearity and time varying, is one of the most complex systems of nuclear power plant. Due to the existence of so-caller "false water level", it is hard to control SG water level satisfactorily by traditional PID methods. The fuzzy control technology does not rely on the mathematic model and has excellent robustness characteristics. It is fit for the control of SG water level.On the basis of study steam generator's operating principle, a fuzzy feedforward-cascade water level controller with a supervision item is designed in this paper. Under this control system the master controller is a FUZZY-I controller. The change of water level and changing rate of water level are designed as the input of master fuzzy controller. The integrator is used to eliminate the steady state error. Slave controller is a single input single output fuzzy control which applied to response quickly due to feedwater disturbance. Fuzzy feedforward item is applied to compensate the impact of measurable disturbance on system output. The fuzzy supervising item is utilized to attenuate the impact caused by non-minimal phase factor. Then the proposed strategy is applied to control of one certain SG water level, the results of simulation show that under this control strategy the system may overcome the disadvantageous influence given by "false water level" phenomena, and it has smaller maximum overshoot than traditional feedforward-cascade PID control system.