Optimization Of Coordination Control System For Thermal Power Units Under Ultra Low Loads

The grid-connected generation of renewable energy as well as the complexity of the power consumer side load cause double random disturbances in the power grid and require frequent and drastic adjustment of the power generation load of the thermal power units to eliminate the disturbance.In particular,the thermal power unit is involved in the deep peak adjustment of the power grid,which is the long-term operation under the ultra-low load of less than 50%,easily results in a series of problems such as instable boiler combustion,low combustion temperature in the hearth and reduced safety of water circulation.Conventional load section coordination control systems,such as turbine following boiler mode and boiler following turbine mode,can only achieve a single control target,such as power or stability of the pre-machine pressure,but will result in fluctuations in the amount of fuel and turbine trim.Excessive fluctuation of the fuel quantity under ultra-low load can cause the fire extinguishing in the hearth,while the drastic change of the gas regulating valve can cause the turbine vibration,differential expansion and axial displacement to increase.Therefore,the unit needs to avoid the fuel quantity and the valve excessive fluctuation in the operation of ultra-low load to ensure the safety and stability of the operation.Combining turbine following boiler mode and boiler following turbine mode control features,this paper designs a flexible control system based on turbine following boiler mode and boiler following turbine mode and builds a flexible factor.By changing the flexibility factor,the system can be switched steplessly between them,and complete the control requirements of multiple control targets(AGC response rate,Boiler stable combustion),while stabilizing the unit operation.This paper analyzes the theoretical constraint relationship between performance index and actuator amplitude through modeling and derivation of transfer function of equivalent controlled object for the coordinated control systems of turbine following boiler mode,boiler following turbine mode and DEB,and verifies the constraint relation between pre-machine pressure and fuel quantity under disturbance of AGC command.At the same time,SIMULINK simulation model based on flexible control system of turbine following boiler mode and boiler following turbine mode is built to simulate and analyze the influence on the flexible control system when the flexible factor is switched at static and dynamic.Finally,the flexible factor is constructed by the weighted algorithm of boiler load and operator.The simulation results show that the flexible factor at the input of the controller will not disturb the flexible control system when it is switched under steady state conditions.However,the flexible factor at the input or output of the controller is switched under changing conditions,disturbing the flexible control system.The flexible control system provides a new idea for the optimization of the coordinated control system of thermal power units under ultra-low load,and has certain reference value.