Research On The Flexibility Improvement Method Of Coal-Fired Units Based On Solar-Coal Energy Complementarity

In order to achieve the goal of " emission peak and carbon neutrality " as soon as possible,accelerating the construction of renewable energy has become one of the effective ways to optimize and reform Chinese energy structure.However,renewable energy power generation has certain time-varying characteristics,which brings a great challenge to the stable operation of the power grid.As the main power generation unit in China,its controllability makes it a regulating power supply.However,coal-fired units have the characteristics of large lag and large inertia.With the large-scale and rapid development of renewable energy,coal-fired units are no longer competent for peak shaving.Therefore,improving the operation flexibility of coal-fired units has become one of the most effective ways to achieve Chinese " emission peak and carbon neutrality" goal.The complementary operation mode of solar-coal energy has made rich research achievements in improving the efficiency of coal-fired units.At the same time,integrating the heat storage link into the solar-coal energy complementary system can improve the energy storage characteristics of coal-fired power generation system to a certain extent,and then improve the operation flexibility of coal-fired units.However,the current research results show that the research on improving the operation flexibility of coal-fired power generation system based on solar-coal energy complementary units is not enough.Therefore,based on the typical solar-coal energy complementary system,this paper uses the method of modeling and simulation to improve the operation flexibility of coal-fired units.The main research contents are as follows:（1）Based on MATLAB/Simulink,modular modeling method is adopted.According to the laws of energy conservation and mass conservation,the mechanism models of key modules such as trough solar collector,heat storage/cooling water tank and oil-water heat exchanger are established by using lumped parameter method.The modules are connected according to the flow direction of working medium in the complementary system,and the mechanism model of photothermal system is established,which can be applied to the study of dynamic characteristics of solar-coal energy complementary system.（2）This paper takes 330 MW coal-fired unit as the research object,and couples the unit with photothermal system.There are three coupling modes: the photothermal system is connected in parallel with No.1 high-pressure heater,the photothermal system is connected in series between No.1 high-pressure heater and No.2 high-pressure heater,and the photothermal system is connected in parallel with No.2 high-pressure heater to form the mechanism model of solar-coal energy complementary system.At the same time,the dynamic characteristics of solar-coal energy complementary units under different DNI working conditions are analyzed.Based on the mechanism model,the step simulation experiments of coal feed rate,the opening of steam turbine regulating valve and the opening of heat transfer oil flow regulating valve are carried out.The effects of different input step disturbances on key parameters such as unit load and main steam pressure are studied.By analyzing the simulation results,the input,output and coordinated control model structure of the coordinated control system are obtained,and the unknown variables in the transfer function are solved by parameter identification.The model basis is established for the subsequent control strategy to improve the flexibility of the unit.（3）In order to improve the flexibility of the unit,two new control strategies are proposed:the first coordinated control system is a "three input two output" structure,which takes the new coordinated control of three coupling modes in series and parallel as the research object.The second new coordinated control system is a new coordinated control system based on multi-scale decomposition of load instructions.Through the step and slope simulation experiments of the two control strategies,and through the comparison of the key parameter images,IAE and ITSE values,it is concluded that in the first coordinated control system,the coordinated control effect of the photothermal system in parallel with No.2 high pressure heater is the best;In the second type of coordinated control system,the combined coordinated control system of parallel No.1high-pressure heater and parallel No.2 high-pressure heater based on multi-scale decomposition of target load signal has the best control effect.It can greatly improve the flexibility of the device.