Research On Key Technologies Of Flexible Operation Control Of Thermal Power Units

The continuous development of new energy power has far exceeded the carrying capacity of China's power grid,and large-scale consumption of new energy power has become a major problem of China's power system.The flexible operation of thermal power units is an important way to solve this problem.In the traditional sense,the unit itself has a certain flexibility,but in the face of the current environment and scheduling mode,its flexibility is far from the actual demand.The design and modification of the unit's main equipment and auxiliary equipment is an important basis to improve the flexibility of the thermal power unit.The operation and control technology is an important measure to deeply explore the flexibility and realize the rapid and deep load change of the unit.The main research direction of this thesis is key technologies of flexible operation control of thermal power units,which is studied from four aspects:optimization control of milling system,optimization control of coordination system,decoupling control of CHP units and multi-energy coordinated control of CHP units.The main contents include:1.Optimization control of the milling system for flexible operation.Considering that the dynamics of the milling system is an important factor affecting the response rate of the boiler,but its typical nonlinear,multivariable and strong coupling characteristics are the main contradictions that limit its response rate to boiler commands.For this reason,considering the principle and characteristics of the milling system,this thesis firstly establishes a nonlinear dynamic model of a milling system based on its mass and energy balance.Secondly,a new method of controlling the output of the milling system by using the coal powder at the outlet of the coal mill is proposed.The multivariable predictive control algorithm is taken as the core to design the control scheme,the compensation control of coal powder at the outlet of coal mill and the energy-saving control of temperature at the outlet of coal mill are also incorporated into the scheme,the effectiveness of the scheme was verified.Finally,the classic drum boiler model is improved based on the analysis of the milling system,simulation results show that the compensation control of primary air can improve the stability of the coordinated control system.2.Optimization control of the coordinated system for flexible operation.Since there is a large delay and inertia in the response from coal feed flow to main steam pressure and mid-point enthalpy,the performance of traditional PID controller with feedforward is poor.To fundamentally solve this problem,this thesis takes the stair-like generalized predictive control algorithm as the core,and combines the traditional feedforward and decoupling control concept to design the coordinated control system.Taking drum boiler and one-through boiler units as examples,the optimization control scheme of the coordinated system is designed based on each dynamics.The effectiveness of the scheme was verified in the laboratory.The results have been successfully applied to a 330MW drum boiler unit in Inner Mongolia and a 660MW one-through boiler unit in Fuzhou,and the performance is well.3.Decoupling control of CHP units for adapting to the deep variable load.Considering that "power determined by heat" is the main reason for limiting the CHP unit to change its load in depth,"thermal-electric decoupling" is an important way to solve this problem.To this end,on the basis of the flexibility transformation of a power plant in Northeast China,this thesis firstly analyzes the influence of absorption heat pump,two-stage bypass and heat storage tank on the thermoelectric characteristics of the unit.The calculation method of the safe operating area is given,and based on this,the thermal-electric decoupling capability and deep peaking capability are analyzed.Secondly,the nonlinear dynamic model of each auxiliary heating system is established,these models are connected according to the heating principle of the plant to form a simulation model of the combined heating system.Finally,a deep decoupling control system is proposed based on the model,which realizes the conventional,shallow and deep thermal-electric decoupling control of the CHP unit,and improves the peaking capability of the unit.4.Multi-energy coordinated control of CHP units for adapting to the rapid variable load.Considering that the CHP unit is a energy conversion system integrating multiple forms of energy in boiler,heat supply network and heat storage tank,there is a certain correlation and complementary characteristics between each form of energy.To this end,on the basis of analysis of the characteristics and limitations of these energies,a global optimization scheme for multi-energy coordinated control is proposed,this scheme is mainly composed of multi-energy coordinated scheduling system(MECSS),distributed energy coordinated control system(DECCS)and multi-energy online evaluation system(MEOES).Secondlly,the implementation methods and main tasks of each system are elaborated.The MECSS mainly completes the processing and distribution of electric load command;the DECCS mainly completes the coordinated control of energy storage in each system;the MEOES mainly performs evaluation of energy storage in each system.Finally,a multi-energy coordinated load control scheme is designed based on the model of the combined heating system,results show that the scheme can effectively cooperate with the each energy storage,the rapid load-changing capacity of the unit is improved and the heating quality of heat supply network is also guaranteed.