Thermal Power Plant Modelling And Control Strategy Of Quick Load Change

With the large-scale renewable energy generation urgently need to be connected to the power grid,the instability of renewable energy,such as wind energy and solar energy,causes coal-fired power plant load commandchange range and rateare growing,some parameters dynamics are relatively violent,which is easy to exceed the safety value based on traditional control technology.Therefore,thermal power plant flexibility needs to be improved.The mathematical model of thermal power plant was established based on the method of mechanism analysis,and the plant dynamics under large disturbance conditions were analyzed.Main parameters control technologies under quick load change conditions were put forward.The improved thermal power plant coordinated controlled mathematical modelssuitable for quick load change conditions were established.Coordinated control technologies of quick load changebased on steam turbine energy storage depth utilization were proposed.The main research contents are as follows.Firstly,a mathematical model of thermal power plant was built up,basing on the balance principles of mass,energy and momentum,using lumped parameter modelling method,introducing the block modelling technology,combining with the relevant empirical formula.The model includes boiler steam-water system,fuel system,feedwater system,bypass system,steam turbine system and other equipment.Model was validated by the field tests of feedwater heater cut-off and put-in,simulation error was within the allowable range,model can be used for the study of dynamicsof thermal power plant under the condition of large disturbance.The control strategies for the main parameters of thethermal power plantfast cut back(FCB)were proposed by simulating the FCBprocess.Secondly,aiming at the quick load change conditions of thermal power plant,combining with the gray correlation analysis,linear active disturbance rejection control(LADRC)and feedforward compensation,the gray correlation compensation control for the speed of feedwater pump turbine was proposed,the active disturbance rejection compensation control technology combined gray correlation(LADRC-GCC)of boiler drum water level was proposed,and the linear active disturbance rejection control combined with feedforward compensation control technology(LADRC-FCC)of steam turbine bypass valve temperature was proposed.The above technologies can effectively protect the key parametersin the safe range,and the control effect was better than traditional control techniques,which laid the foundation for achieving flexibility of thermal power plant.Thirdly,in order to improve the applicability of the thermal power plant coordinated control mathematical model,basing on the mechanism model,under the certain assumptions,the model was simplified.A thermal power plant coordinated control mathematical model considered feedwater system was established.The model was validated by the field test of feedwater heater cut-off.Moreover,a simple and accurate model of thermal power plant suiting for the FCB control technology research was established in this work.The improved coordinated model covers turbine extraction system,steam turbine bypass,and boiler feedwater system.Model inputs were feedwater flow rate,steam turbine throttling valve opening,high pressurebypass valve opening,and coal mass flow rate.Model parameters were identified by 100% economize continue rate(ECR)load FCB field test and validated by 50% ECR FCB field test.The above coordinated controlled mathematical modelswere relatively accurate and can be used for the study for coordinated control technology of quick load change.It provided models support for the research on the coordinated control technology of quickload change.Finally,in order to improve the flexibility of thermal power plant,steam turbine storage was deeply utilized,referring to the thought of "load decomposition,joint control".Thiswork put forward the method of steam turbine extraction steam throttling participation in coordinated control,by using the high-frequency signal part of load command and the main steam pressure deviation signal to control the team turbine extraction steam throttling valve.The work also put forward the method that steam turbine feedwater bypass was involved in coordinated control system,the high frequency signal of load command and the main steam pressure deviation signal control the opening of feedwater bypass valve.The low-frequency signal of the load command feedforward compensation technologywas proposed,and the low-frequency signal of the load command was used as a feedforward compensation signal for the fuel amount command.The above thermal power plant flexibility control technologies can effectively inhibit the main steam pressure fluctuation under the condition of load command changes,reduce the fluctuation of the fuel amount command,and improve the flexibility of the thermal power plant.