Multi-source Coordinated Low-carbon Optimal Dispatching For Interconnected Power Systems Considering Carbon Capture

With the proposal of the national strategy of carbon peak and carbon neutrality,the development and utilization of large-scale new energy and low carbon power generation of conventional fossil energy have become the prominent features of the development of the new power system in our country in the future,and it is an important way to promote the transformation of energy power to the direction of clean and low-carbon.However,on the one hand,the output of new energy is random,intermittent and highly fluctuant.The increase of its permeability in power grid will affect the power flow distribution,aggravate the peak regulation pressure,and bring great challenges to the traditional dispatching decision.On the other hand,coal-fired thermal power is still the main power structure in our country at this stage,whose slow adjustment speed,insufficient adjustment ability and high carbon emissions lead to the poor overall flexible adjustment ability of the system,which is not conducive to the realization of the carbon peak and neutrality targets.Therefore,it is currently a very important research topic how to reasonably and widely allocate flexible adjustment resources,improve the accommodation capacity of large-scale new energy,and coordinate the safety,economy,flexibility and low-carbon operation of different dispatching agents.In this context,the existing coal-fired units can be transformed into carbon capture power plants through carbon dioxide capture technology and coordinated dispatching with other flexible resources can effectively improve the accommodation level of new energy and fully tap the dispatching potential of flexible resources with different characteristics.In addition,considering the cooperative optimization of different dispatching agents and flexible regulation resources can improve the flexibility of multi-dispatching agents and reduce the operation risks of power grid.This paper carries out in-depth research on power system optimization operation from four aspects:more flexible resources coordination,multi-area interconnected coordination.AC/DC hybrid coordination,and multi-level coordination of transmission and distribution.The main contents are as follows:(1)From the aspect of more flexible resources coordination,aiming at the problems of increasing permeability of new energy in power grid and large capacity nuclear power units with full power base load aggravating the peak regulation pressure of power grid,a low-carbon optimal dispatching scheme of multi-resource access with multi-time scale is proposed.Firstly,the net output characteristics and quick power adjustment ability of flue gas split carbon capture power plants are quantitatively analyzed,and the ability of carbon capture power plants to participate in the peak regulation of power grid is evaluated.According to the actual peak regulation experience of nuclear power units,the output characteristics of nuclear power plants participating in peak regulation are optimized to improve the accuracy of the peak regulation model.Secondly,a multi-source coordinated and multi-time scale low-carbon optimal dispatching model with nuclear power units and carbon capture power plants as controllable generation units is proposed.Considering that nuclear power units are more suitable to participate in power grid operation by daily load following in the actual operation process,which can be dispatched in the day-ahead stage.In terms of the lower net output limit and faster power regulation speed of carbon capture power plants,the dispatching potential of carbon capture power plants in different time scales is fully explored.Finally,the simulation analysis shows that the proposed multi-time scale dispatching scheme can relieve the peak regulation pressure of power grid,improve the accommodation level of new energy,reduce carbon emissions,and promote the dispatching flexibility and operation economy of power grid.(2)From the aspect of multi-area interconnected coordination,in order to effectively promote the new energy accommodation of the sending and improve the problem of the receiving power grid’s insufficient flexible adjustment ability,a decentralized and coordinated robust low carbon dispatching strategy for multi-area interconnected power system including nuclear power plants and carbon capture power plants is proposed.Firstly,the mathematical model of the carbon capture power plants with comprehensive flexible operation mode is established,and the range of operating interval of net output power is discussed,so as to give full play to the characteristics of peak shaving of the carbon capture power plants with this flexible operation mode.Secondly,to be compatible with the current dispatching mode in China,the decentralized and coordinated dispatching framework of multi-area interconnected system is constructed based on analytical target cascading(ATC)method,and the optimization problem is decomposed into the master problem of superior dispatching center and the subproblem of subordinate dispatching centers.Among them,the proposed transmission power model of tie-line is considered to be included in coordination and optimization in master problem,and the dispatching plan of tie-line is formulated by superior dispatching center.Meanwhile,based on the robust optimization to deal with the uncertainty of the wind output in subproblem,and the robust unit combination models considering multiple types of flexible resources are established in subordinate dispatching centers.The model is solved by using column and constraint generation algorithm(C&CG)and strong duality theory to realize the coordinated optimization of tie-line and flexible resources in sending and receiving areas.Finally,the simulation analysis shows that the proposed dispatching strategy can effectively improve the accommodation capacity of new energy in the sending area and improve the flexible adjustment ability of load center.In addition,operators can adjust the uncertainty budget parameters according to the actual engineering needs to flexibly change the conservative degree of interconnected power system,to achieve the balance between robustness and economy.(3)From the aspect of AC/DC hybrid coordination,in view of the strong randomness and fluctuation of photovoltaic and load,and the inability of the converter station to control the power flow of all lines,which lead to the increase of safety operation risk of the hybrid system,a low-carbon two-stage optimal dispatching model for AC/DC hybrid power system is established considering safety risk.Firstly,based on the technology of ATC in the first-level optimal dispatching,the day-ahead optimal dispatching problem of hybrid power system is divided into AC-area unit combination,converter station coordinated control optimization operation and DC network optimization operation.A DC power flow controller is considered to be configured in the DC power network,and a multi-period optimization model of DC power network with voltage-change DC power flow controller is established.Secondly,in the first stage of the second-level optimal dispatching,an improved nonparametric kernel density estimation model is proposed to describe the randomness and fluctuation of photovoltaic output and load.A joint probability distribution model of photovoltaic output and load correlation based on Copula theory is constructed,and correlation samples are extracted to calculate probabilistic power flow.The inequality constraints of optimal power flow are modified by reserving enough safety margin.In the second stage,the multi-objective evolutionary algorithm based on decomposition is used to calculate the multi-objective optimal power flow of the AC/DC hybrid system equipped with DC power flow controller,so as to coordinate the economy and low carbon of the system.Finally,the simulation analysis shows that the proposed model can realize the cross-area accommodation of new energy,accurately describe the uncertainty of new energy and load,improve the power flow control ability of DC grid,effectively reduce the operation risk of the system,and provide theoretical support for the optimal operation of AC/DC hybrid power system.(4)From the aspect of multi-level coordination of transmission and distribution,aiming at the problem that the fragmented transmission and distribution dispatching mode is easy to lead to insufficient coordination in the development of power generation and consumption plans between transmission networks and active distribution networks,in the framework of source-network-load-storage interaction,the decentralized coordination robust low-carbon optimal dispatching method of transmission and distribution power system is studied.Firstly,the uncertainty of centralized wind power,distributed renewable energy and exchanged power at the boundary is described respectively by robust optimization method,and the energy exchange interval at the transmission and distribution boundary is described,so a two-stage robust low-carbon optimization dispatching model is established.Secondly,a decentralized coordination two-stage robust dispatching model for transmission and distribution power system is constructed based on alternating direction method of multipliers(ADMM).The optimization problem of transmission and distribution system is decomposed into the transmission and distribution network operators to solve the robust optimization problems of each sub-area respectively.At the same time,an iterative loop method based on ADMM(ILM-ADMM)is proposed,which nested C&CG,to deal with mixed-integer programming and solve the uncertainty problem,and its convergence is proved.Finally,the simulation analysis shows that the proposed method can make the transmission network effectively assist the active distribution network to deal with the uncertainty of distributed renewable energy output,coordinate the uncertainty and adjustment ability of the power transmitted by the boundary,and has significant advantages in protecting data privacy,reducing communication pressure and improving algorithm convergence,which can satisfy the practical engineering application.