| As the last link of power system,distribution network has not only the closest relationship with the users,but also the most direct impact on overall performance efficiency and power supply quality.So that its operation control level is closely related to the quality and reliability of the power supply and consumption.With the gradual increase of the proportion of distributed energy and the development of diversified loads like electric vehicles,energy storage devices and etc,the traditional distribution network can not meet the requirements,so it becomes inevitable to construct the smart distribution network."Distribution network construction and transformation action plan from 2015 to 2020" formulated by the National Energy Board made it clear that “meeting the power demand,improving the reliability and promoting the intelligentialize as the goals,adhering to unified planning and unified standards,overall urban and rural,coordinated promotion as the principles,sparing no effort to solve problem of weak development of distribution network urban and rural,comprehensively speeding up the construction of modern distribution network,supporting economic development and servicing social and people's livelihood."How to ensure the security of distribution network in the case of the access of large-scale distributed generation,and how to use micro grid technology to improve the power supply reliability of system key load,are the focus of research in the power field.This paper is completed at the National High Technology Research and Development Program(863 Program)funding including the following aspects: transient real-time simulation analysis of smart distribution network,real-time self-healing control of smart distribution network and micro grid control,long time-scale operation optimization of smart distribution network.Furthermore,distribution network operation is introduced in planning level,and locating and capacity-determined of micro grid considering the needs of distribution network operation is also researched in this paper.Specific work and innovation is reflected in:(1)Transient real-time simulation modeling of smart distribution network containing distributed photovoltaic power and solid oxide fuel cells is researched in this paper,and real-time simulations of smart distribution network based on real-time simulator RTDS are completed.On this base,the transient characteristics of the system caused by all kinds of disturbances such as changes of environmental conditions,external faults of system and changes of power commands,which might happen when distributed generations connect to the power grid,are analyzed.Then the guiding ideology for transient characteristics analysis of self-healing control of smart distribution network containing a variety of distributed generations is supplied.(2)The system architecture of smart self-healing control of distribution network is established,and self-healing control strategies of smart distribution network containing distributed generation and energy storage devices are proposed,including a focus on risk assessment and prevention control before fault occurrence,and emergency control in fault occurrence,and planning island after fault occurrence.In this way,the possibility of fault is recuded as much as possible to achieve the goal of fast fault response and processing of distribution network,then the power distribution reliability of key users is guaranteed.Results of simulations and experiments verify the correctness and effectiveness of the proposed control strategies.(3)Control objectives of micro grid in the case of self-healing control of smart distribution network are analyzed,and an improved feedforward f-P / V-Q droop double loop control strategy is proposed.This strategy enables the seamless switching between grid connected and grid isolated.When it's operating isolatedly,the changes of micro power or loads can be responded quickly to stabilize the voltage amplitude and frequency of the micro grid.On the other hand,when the grid is connected,real-time voltage signal of distribution network can be followed rapidly to avoid the occurrence of impulse current.Finally,uninterruptible power supply of sensitive critical loads is guaranteed by micro grid,and power supply reliability and power quality of sensitive critical loads is also improved,thus the needs of self-healing control is met.Simulations and experiments verify the correctness and effectiveness of the proposed control strategies.(4)An optimization mode of distribution network operation based on probabilistic power flow is proposed in this paper.In the computation of probabilistic power flow,the uncertainty of wind driven generators,photovoltaic power generations and loads are all considered to reflect the operation characteristics of distribution network in various states effectively.In allusion to the unique mode of closed-loop structure,open-loop operation of distribution network,considering the basic loop matrix,Neighborhood search method is used to solve to ensure that every solution is feasible solution.This traversal strategy based on the basic loop can avoid the local optimum effectively and reduce the computation time.Simulation results show that it can lower voltage deviation of distribution network in different operating conditions and improve the power quality of distribution network with a fast calculation.So that it reflects adaptability of the distributed generation supply and loads fluctuations.(5)The distribution network is extended to the planning level,and a locating and capacity-determined algorithm of micro grid connecting to distribution network is proposed in this paper.First of all,on the two points of view on economy and stability,considering the different control strategies of micro grid,long time scale load parameters are introduced,and optimization configuration mathematical model of micro grid connecting to distribution network is solved by improved PSO algorithm.Examples show that the location and capacity determined by this method in high permeability condition can lower the voltage deviation of distribution network sharply when the micro grid connect to distribution network,as well as the effective improvement of the operation of the system,the reduction of the line losses of distribution network,and the increase of economic benefit of the power grid.The optimization operation and control mothod of smart distribution network proposed in this paper can improve the reliability of power supply of distribution network effectively,promote the power quality,and provide a reference for our future dispatcher control of distribution network. |
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