Research On Optimal Scheduling Of Integrated Electricity And Heat Energy System With Promoting Wind Power Integration

In recent years,with the rapid development of wind power,the total installed capacity of wind power in China has reached 164 GW by the end of 2017,ranking first in the world.Wind power in China is mainly focused on large-scale centralized development and mainly concentrated in the areas of "Three Norths"(northeast,northwest and north China).However,wind power is largely curtailed in integrated electricity and heat energy systems due to the the thermoelectric coupling constraint and the operational principle of "electricity being determined by heat" of combined heat and power units(CHP).In 2017,the total amount of curtailed wind power reached 419 GWh in China.The amount of curtailed wind energy in the"Three North" regions accounted for 99%of the total amount of curtailed wind energy in the country.In some provinces the wind curtailment rate even reaches more than 20%.Wind power curtailment has become an important factor which restricts the further development of wind power.In this dissertation,from the point of view of integrated electricity and heat energy system,we explore some new measures to promote wind power integration and the corresponding optimal scheduling models.This article studies from three aspects,namely power-to-hydrogen,power-to-gas and flexible heat load.Firstly,the dissertation analyzes the main components and characteristics of heat sources,heating network and heat users in the central heating system.Based on the analysis,the overall structure of the integrated electricity and heat energy system for wind power integration is constructed.The definition and characteristics of system flexibility are summarized.Based on the mechanism of supply and demand of system flexibility,the supply and demand of the flexibility of the sources,networks,loads and storages are quantitatively analyzed.According to the principle of system flexibility balance,we analyze the key factors that affect the wind power integration in the integrated electricity and heat energy system from a new perspective.The scheduling framework of integrated energy system is established and the mathematical principles of deterministic optimization scheduling,rolling scheduling and scenario-based stochastic scheduling model are analyzed,which lay the foundation for the research of optimal scheduling of integrated energy system.Secondly,based on the idea that hydrogen can be used for power generation and hydrogen trading market after hydrogen energy is converted into hydrogen,we propose a method to promote wind power integration by introducing power-to-hydrogen system which includes hydrogen sales.Power-to-hydrogen system is modeled,and then a two-stage stochastic scheduling model of the integrated electricity and heat energy system considering the power-to-hydrogen system is established.The first stage is the pre-scheduling scheme under the wind power forecasting scenario,which is used as the implementation plan of the outputs of CHP units and heat storages.The second stage is the re-scheduling plan after the error scenarios are realized,which ensures that the power-to-hydrogen system and the conventional power generating units have enough adjustment ability to deal with all possible wind power prediction errors.The model takes into account the constraints of the sales of hydrogen and the capacity of hydrogen storage.Through the simulation,we analyze the benefit of power-to-hydrogen system in promoting wind power consumption and study some other factors which influence the system operation such as the installation location of power-to-hydrogen system and the price of hydrogen.The results demonstrate the effectiveness of the method.Thirdly,In the context of integrated electricity-heat-gas energy system,a method of promoting wind power integration by using power-to-gas is proposed:by utilizing the large-scale gas storage capacity of natural gas systems,excess wind power can be converted into natural gas by power-to-gas technology,and then the natural gas can be converted into electricity and heat when necessary.An optimal scheduling model of integrated electricity-heat-gas energy system considering power-to-gas is established based on the requirements of power supply,heat supply and gas supply,aiming at minimizing the the operating cost of the integrated energy system.The model takes into account the constraints of the natural gas network,power system and heating system.The simulation results show that power-to-gas can effectively promote the wind power integration and reduce the operating cost of the integrated energy system.Moreover,power-to-gas can reduce the congestion of transmission lines and increase the pressure of the vulnerable nodes in the natural gas network.In addition,the electricity and thermal load level will influence the operation of the power-to-gas.Fourthly,starting from the heat demand side,a method of improving the operational flexibility of CHP units by using the adjustablity of building thermal load is proposed,which also creates the favorable condition for the promotion of wind power integration.Firstly,based on the heat balance equation of buildings,the mathematical relationship between the indoor temperature,outdoor temperature of the building and the heat load of the building is established.The mathematical model of the flexible heat load is established while keeping the indoor temperature of the building within the temperature comfort zone of the users.Then the flexible heat load is integrated into the optimal scheduling system of integrated electricity and heat energy system.The scheduling model takes the user's comfort,power trading and interruptible load into consideration.In addition,a rolling scheduling model based on the model predictive control is established considering the wind power and temperature forecasting errors and the time correlation of indoor temperature of buildings.The model can be divided into two stages:the day-ahead scheduling and intra-day scheduling.In the intra-day scheduling stage,rolling optimization and feedback correction are considered to improve the accuracy of the optimal scheduling.The simulation results show that the proposed method can make use of the flexibility of building thermal load to enhance the flexibility of CHP units,reduce the power and heat outputs of CHP units during the period of high wind power,and then provide more space for the promotion of wind power.