Research On Modeling And Coordinated Control Optimization Of Supercritical Units

In the specific historical period of large-scale interconnection of new energy sources,the role of thermal power units has being gradually transformed from the traditional main power generation unit to the main peak and frequency modulation power unit,which means better response capability of thermal power units are needed under fast load-changing conditions.Thus,there is an urgent need for thermal power flexible transformation.At the same time,with the supercritical units becoming the main thermal power supply,it is very meaningful to carry out the research on modeling and coordinated control optimization for supercritical units.The performance of coordinated control system is poor,due to lower heat storage capacity and strong nonlinearity in supercritical units.At the same time,compared with the subcritical unit,the operating pressure and temperature of the supercritical unit are higher.The working temperature of the superheater is close to the tolerance limit of metal materials,which caused frequent occurrences of bursting accident.This seriously affects the safety and economics of the unit operation.In order to carry out the above research,a supercritical unit model for characteristic analysis and controller design is established by the method of mechanism modeling.The model parameters are identified and verified by the actual operation data of the supercritical unit,and the model characteristics are analyzed.The simulation model of the coordinated control system of supercritical units is established based on a control logic applied in unit.Then the typical control logic is analyzed in detail,which lays a foundation for the subsequent optimization of the control system.Secondly,in order to effectively evaluate the optimization effect of the control system,the evaluation index for evaluating the flexibility control performance of thermal power units is selected and defined.Based on the analysis of AGC command signals,the division and judgment rules of AGC load demand states are established.By using different load command speed limit strategies in different states,the variable speed limit optimization based on the current load demand state is realized.Simulation results show the effectiveness of the optimization strategy.In view of the contradictions and deficiencies in the fuel calorific value correction logic,the disadvantage of fast adjustment of BTU correction coefficient for temperature control is proved by simulation experiment.The strategy of calculating fuel calorific correction coefficient is reconstructed so that the influence of load-heat nonlinearity on the calculation of BTU correction value is eliminated.Finally,aiming at the problem of safety control of superheater body,the direct cause of superheater tube explosion is analyzed from the point of view of temperature control.And the functions and shortcomings of the existing superheated steam temperature control system is analyzed.The above analysis reveals that the effective means to realize the safety control of superheater body are to prevent wall temperature from overheating and frequent flu ctuation.Based on the original steam temperature control logic of the unit,the optimization of steam temperature control system is carried out.The temperature setting values of each link in the superheated section is dynamically adjusted through the design of forward anticipatory control loop,backward regulation control loop and reverse compensation control loop,by which the optimal control of superheated steam temperature and superheater wall temperature is realized.In particular,the corresponding safety protection logic is designed to deal with the abnormal overtemperature of superheater wall.