Research On Stochastic Planning Method For AC/DC Hybrid Microgrid And Its Clusters

The AC/DC hybrid microgrid,that does not need a large number of converter links and converter devices,has the advantages of simple structure,low operating loss,and flexible network regulation and control,and its scale can be continuously expanded through interconnection of microgrid clusters.However,the strength of the upper-level distribution network,the dynamic factors existing in the engineering cycle and the uncertainty of the output of the distributed generation(DG),will influence the planning and operation of AC/DC microgrid and its clusters.In this thesis,considering the above factors,a scientific and reasonable planning method is studied of optimization of AC/DC hybrid microgrid and its cluster.The work of the thesis includes the following:(1)Basic model of AC/DC hybrid microgrid and the uncertainty analysisBy analyzing the basic structure and operation mode of the AC/DC hybrid microgrid,as well as the faults and transfers of the power supply path between the distribution grid and the common coupling point of the microgrid,a method is proposed for computing the off-grid operation probability of the microgrid.According to the operating characteristics of the micro-source,the output power model is established,including wind turbine,photovoltaic output power model and battery energy storage lifetime model.Then,the stochastic characteristics are analyzed of DG output and the techniques of random scene generation,fusion and reduction.This basic model and uncertainty analysis method provide the basis on which the modeling and solution of the subsequent microgrid stochastic planning are carried out.(2)Single-stage stochastic planning method of AC/DC hybrid microgridConsidering the influence of the structure of distribution network and the uncertainty of DG output on the operation of microgrid,the off-grid operation probability and the output power model of micro-source is embedded into the planning problem based on DG stochastic output scenario for carrying out integrated optimization modeling.In this model,the objective function is the sum of the investment costs of DG,energy storage and converter in the microgrid,and the expected value of the operating cost of each random scenario in the connected-grid and off-grid mode,with the associated constraints from the installation and operation random scenarios in conneted-grid and off-grid modes.The nonlinear problem is transformed into a mixed integer programming model by putting into 0-1 integers and real variables.The case study verifies the economy and robustness of the microgrid stochastic planning method by analyzing and comparing the influence of upper-level distribution network structure,project duration,and DC load ratio on the microgrid power planning scheme.(3)Multi-stage stochastic planning method of AC/DC hybrid microgridAccording to the dynamic factors,which includes the staged alteration of the upper-level distribution network,the reduction of micro-source costs and the load growth,the microgrid planning period is divided into multiple stages,and a high reliability distribution network transformation scheme is proposed for meeting the demand of users for reliability.Based on the single-stage stochastic planning model of the AC/DC hybrid microgrid,taking the minimum sum of the comprehensive costs of all stages as the objective function with the installation and operation constraints of each stage,and a multi-stage optimization configuration model is thus established and solved.According to the actual project,the alteration of each stage of the distribution network is determined and the improvement effect on the off-grid operation probability of the microgrid is verified.The case study compares and analyzes the economy of the yearly planning and multi-stage planning of microgrid,and verifies the robustness and economy of the microgrid multi-stage stochastic planning method with multiple dynamic factors.(4)Multi-stage stochastic planning method of AC/DC hybrid microgrid groupConsidering the limited capacity of a single microgrid,multiple AC/DC hybrid microgrids are combined into microgrid clusters,and the basic structure and typical operating mode of the microgrid clusters are analyzed.The sub-microgrids are encouraged to operate through short-term interconnections to ensure reliable power supply for important loads through off-grid operation.Based on the multi-stage stochastic planning model of the AC/DC hybrid microgrid,with the minimum sum of the integrated costs of multiple microgrids taken as the objective function,and considering comprehensively the installation constraints of each stage and the operational constraints of group grid connection and group off grid,the AC/DC Multi-stage optimal configuration model of DG is developed,as well as those for energy storage and converter in the hybrid microgrid cluster.The case study compares and analyzes the planning method of the microgrid cluster system considering short-term interconnection and the multi-microgrid system neglecting the energy cooperation,the results of which demonstrates the robustness and economy of the microgrid cluster stochastic planning model.