Reseach On A Control Method Based On Gain-switching For Intermediate Point Temperature Of Supercritical Pressure Boiler

As the advanced signal of main-steam temperature control,the control quality ofintermediate point temperature in supercritical boiler is directly related to coal-water ratioin the supercritical boiler and the quality of the main-steam temperature,and related to theeconomy and security of units.There are two control schemes of the intermediate pointtemperature at present,which are schemes by correcting the flow of feedwater andcoal.When use the method by correcting the flow of coal to control temperature,waterflow do not change frequently. However,this method exist large time-delay,wnich havebad influence upon the economy of operation. The method by correcting the flow offeedwater can regulate the temperature quickly,which keep the intermediate pointtemperature within a narrow rang.However, frequent changes in water flow lead to thefluctuate of separation.It can result in local over heating in low load,which threat to thesafety of operation. The paper put forward a combination of two present methods on thecontrol of coal-water ratio,and introduce a gain-switching control scheme to achieve thecontrol quality of intermediate point temperature.This paper makes a thorough analysis on the research object of a660MWsupercritical boiler.Focus on the static effect of main parameters in supercritical unit fromthe disturbance of heat and water flow.An approximate calculation is made to achieve theamplification factor.On this basis,a distributing parameter model is made. The analyticalsolution is simplified by using the method of undetermined function to achieve thetransfer function.In order to solve the problem of a big hysteresis,large inertia system,thispaper simple active disturbance rejection control to linear.Apply the liner activedisturbance rejection control to the control method by correcting the flow of coal.Theintermediate point temperature deviation and its rate of change is used as judgingcondition. When the intermediate point temperature’s deviation and rate of change aresmall,it uses the method by correcting the flow of coal with linear active disturbancerejection controller. When the intermediate point temperature’s deviation and rate ofchange are large,it uses the method by correcting the flow of feedwater with PIDcontroller.Based on the idea of fuzzy control,putting forward the strength coefficient toaccomplish non-disturbance switching between the two coal-water ratio controlmethod.Make a simulation on distributing parameter model of a660MW supercriticalunits by using the novel control scheme under three typical working conditions. Simulation results show that the gain-switching control scheme combines the advantagesof the two existing control scheme. This method resolves the contradiction between theregulating rapidity of intermediate point temperature and the stability of separation.It issatisfactory on the control of the intermediate point temperature under different loads.