Research On Electricity-heat Coordinated Control Of Once-through CHP Unit

In order to adapt to China’s " carbon peak and carbon neutrality" development goal,coal-fired units need to transform and develop from basic supporting power sources to flexible power sources that support the consumption of new energy.The modification of existing coal-fired unit heating part can improve energy efficiency and achieve energy conservation and consumption reduction.Currently,there are many supercritical units electric power plants have completed heat supply transformation in China.With the continuous promotion of policies such as " increasing the size of large units to reduce the size of small ones " and heat supply transformation,the proportion of Once-through CHP Unit in China’s thermal power installed capacity will continue to increase.However,the operation mode of " determining power based on heat" of this type of unit limits the variable load capacity,making it difficult to meet the assessment requirements of automatic generation control(AGC)in the power grid,which contradicts the development requirements for improving the new energy absorption capacity of the power system.In addition,(ultra)supercritical units use once-through boilers,where is no obvious steam water separation interface,makes the modeling and control of such units more complex than drum boiler units.To address these issues,this paper aims to achieve rapid response to grid load demand on the power supply side of the electric power system,takes the Once-through CHP Unit as the research object,conducts research from two aspects:unit dynamic characteristics and coordination control strategies for electric load and thermal load.The main work of the paper includes:(1)Based on the method of mechanism modeling and data identification,a simulation model of the coordination of electric and thermal power of Once-through CHP Unit is established.Based on on-site operation data,a dynamic characteristic model the unit’s thermal-electric conversion about the impact of heating extraction flow disturbance on the power generation load of the unit is established.A nonlinear control model of coordinated control of once-through boiler CHP units is established by integrating this model with the traditional coordinated control model of the unit and boiler.(2)An electricity-heat coordination control strategy which is combine the thermal load active response and self-recovery is proposed,which improves the operational flexibility of the unit.Use the dual control scheme,the unit’s power generation load control is divided into two load control loops:the main loop is the heating and steam extraction regulation loop,which uses its fast response characteristics to improve the unit’s load change rate;the secondary loop is the fuel quantity regulation loop to ensures the power supply and heating recovery throughout the entire regulation process.At the same time,using the integral mean value theorem,a parameter signal Dh that can reflect the changes in the heating load during the entire adjustment process is reconstructed to avoid affecting the user experience of the heating network during the load change process.(3)Taking a 1000 MW unit as an example,simulating the actual variable load operation of a power plant verifies the effectiveness of the control strategy proposed in this paper.After the standby unit has been operating stably,by applying different types of load commands to the unit,to compare the unit response curves,various assessment indicators and heating recovery effects under the two strategies.The results show that the unit’s load change rate under the control strategy proposed in this paper is better than that under the general coordination control strategy,and the comfort level of the heating network user is not affected.