Research On Voltage Fluctuation Control Of DC Bus In AC/DC Hybrid Microgrid

As a renewable energy utilization form combining the advantages of DC microgrid and AC microgrid,AC-DC hybrid microgrid has attracted more and more scholars'attention.Because there are many micro-power sources in AC/DC hybrid microgrid,how to coordinate the micro-power sources to ensure the stability of DC bus is a key point in the research of AC/DC microgrid.In this thesis,the purpose and significance of the research is described,and the current situation of dc bus control technology at home and abroad is analyzed.Then,by analyzing the micro-grid architecture,the ac-dc hybrid micro-grid is taken as the research target,and the ac-dc hybrid micro-grid architecture used in the experiment of this topic is designed,and the system capacity configuration required by the experiment is explained.The principle of photovoltaic power generation system,battery energy storage system,diesel generator simulation and simulation model in MATLAB/simulink are introduced.The voltage grade selection and stability deviation of dc bus are analyzed.Secondly,the influence factors of dc bus fluctuation are analyzed.In order to ensure the stability of dc bus and coordinate the distributed generation,energy storage device and load,a coordinated control strategy based on dc bus voltage is designed.According to the voltage range of the dc bus,the control strategy determines the critical threshold of each micro power supply and divides it into four modes.According to the state of controller in each mode,the stability of dc bus is realized through cooperative control.Aiming at the defects of conventional droop control,an improved droop control strategy is designed,which can improve the voltage drop of dc bus and inhibit the circulation caused by the unbalanced output voltage of the parallel converter.Finally,the AC-DC hybrid micro-grid platform and a two-photovoltaic DC micro-grid platform are built in MATLAB/simulink software,and the coordinated control strategy and improved droop strategy are simulated and verified respectively.The simulation results show that the coordinated control strategy based on DC bus voltage can coordinate the micro-power supply and stabilize the DC bus voltage within the voltage deviation range.Compared with the traditional droop control strategy,the improved droop control strategy can effectively suppress the circulating current and increase the voltage drop deviation by about 1.2%.The deviation of DC bus voltage is stabilized within the range of rated voltage± 10%.