Research On Super-critical Thermal Unit Dynamics Of FCB Process

In the past few decades,large-scale blackouts at home and abroad have occurred from time to time,which has caused great inconvenience and heavy economic losses to the people's production and life,and has even caused casualties.The electric power researchers have carried out many explorations and experiments and put forward a variety of coping strategies.The rapid load shedding of the unit is undoubtedly one of the great ideas.The supercritical unit with Fast Cut Back(FCB)function can quickly disconnect the unit from the power grid in the event of a power grid failure,allowing the unit to quickly load-reject the plant and operate in isolated islands.After the power grid fault is discharged,it can quickly increase the load as the power grid start-up power.FCB has greatly accelerated the speed of grid recovery,reduced the time of large-scale power outages,and reduced the number of unit shutdowns.Its economic significance and social significance are self-evident.The FCB unit required the unit to cut the load to the power load with the plant in a short time.The parameters of the various parts of the FCB unit change very violently and pose a threat to the safe operation of the unit.Therefore,the control system of the unit needs to have fast response and rapid action performance.This research establishes the dynamic model of the main part of the unit in order to explore the dynamic characteristics of the super-critical unit FCB process,and provides a reference for the design of the unit controller.Firstly,the dynamic mathematical model of supercritical unit super-heater was established by using mechanism method,and the FCB simulation experiment was conducted on MATLAB.The comparison with historical data shows the correctness of the model.According to the simulation results,the dynamic processes of main-steam pressure and temperature in the FCB process are similar,and they both climb quickly first at FCB initial time and then the volatility decline and gradually to a steady state.The main steam valve opening step disturbance simulation test was conducted to further investigate the dynamic response characteristics of the main steam.The main steam pressure response speed was faster than the main steam temperature response speed.Then,the transfer function model frame of the bypass valve opening-bypass pressure system was selected according to the characteristics of the thermodynamic object with self-balancing capability,and the parameters of the bypass valve system were identified by the particle swarm optimization algorithm(PSO).The transfer function model of the bypass system of the steam turbine was obtained.And the advantages and disadvantages of the differential-smooth film controller and the traditional control was compared,the simulation results showed that the derivative-based sliding film controller had better tracking control effect and is superior to the traditional sliding film controller.Finally,the dynamic mathematic model of the built-in deaerator was established by the partition method.The FCB simulation test was conducted to obtain the dynamic process of the deaerator pressure and water level in the FCB process of the unit.The dynamic characteristics of the deaerator water level and pressure during the FCB process were analyzed.The control strategy of the deaerator water level and pressure was proposed to ensure the parameters of the deaerator during FCB process within safe limits.