Research On Control Stability Of AC Microgrid In Island Mode

With the increasing shortage of primary energy and the aggravation of environmental problems,the traditional energy consumption structure is facing severe challenges.New energy sources,such as wind energy,solar energy,and water power,have become the focus of academic research and direction of electric power industry for their renewability and environmental friendliness.As the best form of equipment to accept new energy generation,microgrid and researches about it can effect the future of China power industry,even the process of Energy Internet directly.At present,there are mainly two problems in the study of new energy power generation technology and microgrid technology.The first is the power fluctuation of new energy power generators,which can result in power unbalance.The second is that there is a large number of electronics device in microgrid,and too fast regulation speed of them can reduce control system inertia.Both of the problems set a higher request for the safe and reliable operation of microgrid.In order to realize the breakthrough in this field,the research on the stability of microgrid control must be deeply studied As the necessary conversion equipment between new energy power generators and microgrid,VSC and its control capability directly determine the control stability of microgrid system.Although related studies are conducted in this field,there are still lots of problems to be studied.In particular,the system-level stability analysis that takes into account the coordinated control strategy between VSCs remains to be further explored.Above all,this thesis conducted the following works:1)First of all,this thesis started with individual VSC control structure and established a complete small-signal-model of VSC with droop control strategy in the environment of resistance lines.Then we analyzed the fluence of control parameters of individual inverter control stability according to the model quantitative analysis The reseach provided an effective theoretical basis for the selection and correction of control parameters.2)Secondly,taking the otherness of line impedance into full consideration,this thesis builded the model mentioned above and verified the effectiveness of the ‘virtual impedance technique' in the decoupling of droop control power.The principle of virtual impedance configuration was also given in this part.3)At last,the small-signal-model of the classical mocrogrid system in island mode was established and the influence of various control parameters on the stability of holonomic microgrid model wass studied.The model was built by combining the droop control model,constant power model and load model.Based on the model,the influence of various control parameters on the stability was discussed and corresponding recommendations for the microgrid controller configuration parameters was given.This part is the most important and innovative technical point of the research,and of great significance to the research on microgrid stability.In summary,on the basis of the previous achievements,the system level con trol model of microgrid islanding mode was established and improved in this thesis,and it was more responsive to the state of microgrid systems.Based on the model,some suggestions for the configuration of the control parameters in the system were put forward with the stability analysis of the microgrid system.This thesis is aimed at the study on the influence of the various parameters of the microgrid on the stability of the system.The influence of various parameters of microgrid on system stability is studied,and the internal mechanism is also analyzed in this thesis,which can provide strong support for the design and operation of AC microgrid.