Research On Key Technologies Of AC/DC Hybrid Microgrid

The dissertation is supported by the international science cooperation projects,named “Optimizing Operation and Control of Micro-grid Integrated by Distributed Generations”(No.2011081054).It is proposed to aim at increasingly intensifying air polluted,increasingly scare fossil energy and low efficiency renewable energy resources.Microgrid brings great convenience and chance for solving many problems of utility grid,which also provides new ideas for utilizing various distributed generations high efficiently.Recently,the topics related to AC/DC hybrid microgrid are researched extensively by Scholars from worldwide,certain results have been achieved in many aspects.However,AC/DC hybrid microgrid is extremely complex distribution network,there are some problems of the whole system including cooperation control,economy,reliability and optimization,etc.the technologies are not yet mature.Hence,the research on key technologies about aforementioned problems has important theoretical value and current significance.According to the aforementioned problems about AC/DC hybrid microgrid,a combination of theoretical analysis,structure modeling,simulation and experiments are employed in the dissertation.Pay attention to the research about control strategy,economy,effectiveness and optimization of AC/DC hybrid microgrid.The research content is as follows:Building the model of AC mcirogrid,DC microgrid and AC/DC hybrid microgrid.The operating principles are analyzed in detail based on their modeling.Three control modes widely used including P/Q control,V/f control and droop control are analyzed and compared.The use occasion is opointed out.The droop curves are depicted and control principle are analyzed in detail.The simulation is done to verify the control principles.According to the problem of distribution power at rated power in traditional droop control.The maximum cost linear droop control function is presented bases on establishing generated cost function.That is the relationship of maximum generated cost and minimum frequency,maximum generated cost and voltage.The experiments circuit is built,for microsources,which is to test the inverse relationship of the power generation and generated cost.For microgrid,which is to verify small frequcency variation,steadily operating and low generated cost.Hierarchical control strategy can solve the problem of various levels of power source in DC microgrid which are put to run in different time sequence.Becausede of the resistance of transmission line,power distribution is unreasonable among the microsources.Therefore,the improved multimodes control is presented,that is V/P droop control.Multistage DC microgrid is proposed based on various levels voltage dc microsources and dc loads.Structural model is constructed and all mode operation principle is analyzed in detail.As an example of neighbour two dc bus,the neighbor bus power transmission is deduced deeply.Two levels dc microgrids is built to verify the saving converters and higher effectiveness.According to the existence problems of AC/DC hybrid microgrid cooperation control,the operating principle of grid-tied and islanded is analyzed deeply.Grid-tied operation,as a reference of dc bus voltage,improved dc droop control is put forward.The size and direction of bidirectional AC/DC converter is deduced.Islanded operation,as a reference of ac bus frequency,improved ac droop control is put forward.The size and direction of bidirectional AC/DC converter is deduced.Combined with the above two cases,a normalized approach is proposed,power transmission formula is detailed derived and control flow chart is researched.The Superiority of above control method is verified through simulation and experiment.According to existence problems of microsources optimization in AC/DC hybridmicrogrid.The combination of improved particle swarm optimization and some advantages of NSGA-II,hybrid intelligent optimization algorithm is advanced.The proposed algorithm Optimal solution optimization and convergence are verified with three basic test function.Applied to microgrid,objective function and restrictions are appropriately selected.TOPSIS strategy is used to get the optimal configuration scheme.As case of location and capability of distributed power and storage battery,the simulation results improve the proposed optimization.