Study On Fast Response Characteristics Of Primary Frequency Modulation For Heating Supply Units

With the establishment of the UHV interconnected power grid and the random and volatile solar energy and wind energy,new energy sources are connected to the grid,the pressure on grid frequency stability is increasing.In the Three North Region,China has vigorously developed combined heat and power units to achieve district heating,and new energy resources are also abundant.In order to absorb more new energy and improve the stability of the power grid,it is urgent to study the participation of heating units in the primary frequency regulation of the power grid.This article takes a typical extraction type heat supply unit as the research object,and comprehensively analyzes the structure of the steam turbine system and the computer theory of the thermal system.According to the hierarchical modeling thought of complex systems,the steam turbine system is divided into different basic computing units for modeling research.According to the mathematical model,a simulation model such as the regulating stage,pressure stage group,heater,deaerator,and condenser of the steam turbine system is sequentially built on the MATLAB/Simulink simulation platform and packaged into subsystems.The subsystems are then connected together to form the overall simulation model of the steam turbine system.The calculation of the thermal properties of water vapor used in the modeling process is based on IAPWS-IF97.MATLAB programs are written and packaged into modules for calculation calls.The relative error between the simulation results of the model and the design value of the heat balance diagram is within 2%,which agrees well with the experimental disturbance curve,which verifies the correctness of the model’s static and dynamic calculations.Based on the simulation model,the primary frequency regulation characteristics of heating units are studied.Under the heating condition,the unit’s frequency regulation ability is insufficient,and the larger the heat extraction steam flow,the less the frequency regulation response ability,which is mainly reflected in the insufficient response amplitude.In order to improve the frequency response of the unit under the heating conditions,the heat storage network energy storage and condensate water throttling were involved in a frequency modulation simulation study.Through the operation of the heating fast-closing valve opening,the heat network energy storage is used to participate in the primary frequency regulation of the unit,which significantly improves the frequency regulation ability of the unit under heating conditions,and the response rate is better than the non-heating conditions.For a 300 MW unit,a 3%～5% action of the heating fast-closing valve can meet the requirements of a general frequency modulation load.A 7%～12% action combined with a high-adjustment door can meet the maximum load command,which significantly improves the unit’s load response capability.Condensate throttling is not ideal for participating in one frequency adjustment under unit heating conditions,especially under large heating conditions,Under the heating conditions,the heat extraction steam supply causes the inlet steam flow of the low-pressure cylinder and the extraction quantity of each low-pressure cylinder to be greatly reduced,so the condensate and low-pressure extraction quantities are small.Very small,the unit load response is not obvious.Under the heating conditions,the unit should improve the primary frequency response capability of the unit through heat network energy storage.