Research On Optimal Placement Methods Of Energy Storage Devices For Improving Micro-grid Transient Stability

With large-scale distributed generations(DGs)connecting to grid,it brings same benefits to the power system.However,it also brings an impact to the stable operation of the power system due to the intermittent of distributed energy.In order to improve the scale of DGs connecting to grid,the method of combining energy storage technology and DGs has attracted the attention of people.And,the effects of energy storage devices(ESDs)have a close relationship with its installation and capacity.Base on the above understanding,the optimal placement of ESDs in interconnected microgrids(MGs)has been researched in detail and depth in this thesis.1.The current energy crisis and environmental problems are firstly summarized.Then the main problems of DGs connecting to grid are analyzed,and using energy storage technology to solve the problems is put forward.And then,the optimal placement of distributed energy storage is introduced.Finally,the research status of energy storage devices and the optimal placement of ESDs in MGs are elaborated.2.The Lyapunov’s theory of stability is first studied.Then,the problems of traditional energy function used in the analysis of MG transient stability are analyzed.The MG transient energy function based on simple model is builded.And then,the MG structure preserving energy function is builded,which is a powerful tool for analyzing transient stability and optimizing placement of ESDs in MGs.3.In order to solve the transient stability problems of MG and large power system interconnected system,using ESDs for achieving partition decoupling control of interconnected system is proposed,which is proved to be feasible through theory analysis.The optimal placement of ESDs in interconnected system is researched for mitigating the amplitude of power on transmission line of interconnected system.4.The problems of using ESDs for improving transient stability of MGs interconnected system are studied.Then two kinds of special cases in the interconnected system are researched:with one or two ESDs installed on transmission line,how it affects the fluctuation of transmission line power;the transient stability of interconnected system is studied when ESDs cannot fully absorb the power fluctuation.Finally,the optimal location of ESDs determined by voltage security domain method is studied.5.The optimal placement of ESDs in multi-microgrids interconnected system is researched,which will adopt a new optimization method called MG branch transient energy function method.The method is builded based on MG structure preserving energy function,in which the external potential energy of MG structure preserving energy function is equivalent to each branch.By looking for maximum potential energy branch,the weakest branch of the system will be determined.Thus,the optimal location of ESDs is determined.Finally,main concluding remarks are summarized and presented at the end of this thesis as well as some interesting problems which deserve further study.