Water Level Control Research Of SG Based On The Two Channel Control Valve

There are a lot of scholars have paid attention to improving the control performance of the steam generator water level control.The dynamic performance of the steam generator water level control system is complex,and this system is containing typical nonminimum phase link.Operation of steam generator which is safty and stable with efficient is the basis to ensure the safty of the primary loop,the second loop and the generated output.So the subject of steam generator water level control needs to be continuously researched until to overcome this problem.The feedwater control valve which is the actuator of the steam generator water level control system is an important part of control system,whose regulation performance to feedwater flow is closely related with the system control ability.At present the steam generator feedwater system exists some problems at low power,such as the control valve movementing frequently,control valve opening too much and clamping stagnation caused by imprecise measuring results and the small flow control of the large channel.To solve these problems,the feedwater sysytem of nuclear power plant gives two solutions at present.One is setting main feedwater loop and initating feedwater loop in parallel,the other one is parallelly installationing the main feedwater control valve and the bypass feedwater control valve in the main feed pipe.However,aiming at these problems this paper proposes a new solution namely two channel control valve.A cold experiment system is set up to study the false water level problem of the steam generator water level control system.This cold experiment system can be used to simulate the thermal state physical phenomena of the steam generator.Main channel control valve flow characteristics experiment,bypass control valve flow characteristics experiment and water level transfer experiment of steam generator was carried out on this experiment system.The experimental datum of water level varied with feedwater flow,water level varied with draining flow,water level varied with bubbles suddenly appearing and suddenly disappeared.The experimental datum are used as the input and output values of the model identification.The matlab system model identification box and curve approximation method are used to identify the experimental system mathematical model of the steam generator.The identified model curve is highly fitted with the experimental curve.The theoretical research and simulation result show that the internal model controller of the steam generator water level control system has good control performance and robust stability.The internal model controller is designed as the feedback controller of the closed-loop system and PI(D)controller is got as the feedforward controller of the closed-loop system.The result of simulation shows that the present feedforward-feedback variable gain multi-model structure controller of the steam generator water level has good control performance tracking control well.Finally,two impulse water level control method is selected to design the water level controll system on the basis of PLC.Consequently,the control strategy designed in this paper has the engineering implementation capability.The two channel control valve design idea is proposed in view of the feed water flow control problem.A larger valve head and a smaller valve head in the same body is designed,which can control the big and small flow use one control valve.The numerical calculation model of the control valve passageway is established by fluid dynamics software Fluent.The numerical simulation has been done with the internal three-dimensional flow field of the main feedwater control valve,the by-pass feedwater control valve of main valve and two channel control valve based on the experimental data.The flow characteristic and resistance characteristic of the main feedwater control valve,bypass feedwater control valve and the two channel construct control valve have been gotten.Simulation results show that the flow characteristic of two channel control valve is similar to the main control valve when the main channel is used alone.The valve flow characteristic with low power channel working alone still can meet the requirement of small flow control,while there is a larger different to bypass valve of the flow characteristic.These work characteristics prove that the two channel control valve has great value of research and development.