Control Strategy Of Interconnected Converters In AC/DC Hybrid Microgrid

Energy has always been a booster for the development of human society.Faced with the increasingly severe problems of fossil energy depletion and environmental pollution,renewable and clean energy has attracted more and more attention.In order to better solve the problem of local consumption and grid connection of renewable energy,the microgrid came into being.With the increase of the DC characteristic load such as electric vehicles,AC/DC hybrid microgrid as a typical form of microgrid can better accommodate distributed power and load with different AC and DC properties,reducing the transformation link,and the AC and DC subnets can be combined with a separate grid and have a flexible operating mode.As an important link between AC and DC subnets,interconnected converters play a role in maintaining the power balance of the microgrid and the stable operation of the supporting system.Therefore,the research on interconnected converters has great practical significance and application value.In this paper,the three-phase two-level interconnected converter is taken as an example to analyze the operating characteristics and control strategy of the interconnected converter.In this paper,the overall structure of AC/DC hybrid microgrid is introduced from two aspects: variable grid and fixed grid.The effect of variable grid structure on power balance between subnets is analyzed,and the fixed grid structure is detailed.The grid structure and the number and types of micro-sources contained in this paper and the corresponding control strategies are described.The control and modeling of photovoltaic,battery and interconnected converters are studied in detail,and Simulink simulation is built.Secondly,the research analyzes the comprehensive droop characteristics of AC and DC subnets.Based on the comprehensive droop characteristics,the typical three interconnected converter control strategies are studied,namely,double droop control,unitized control of droop characteristics,and based on unitized mixed droop characteristics.Through the mathematical theory,the operation characteristics of the control strategy and the selection of the active reference value are analyzed.It is concluded that the traditional converter control strategy will generate unnecessary power flow,which may cause the operating subnet in the interconnection to deviate from the rated state to a large extent.Finally,for the research of typical interconnected converter control,an interconnected converter control strategy based on mode switching and integrated droop control is proposed.The operation rules,mode selection and application scope of the control strategy are analyzed.The comprehensive droop coefficient is derived and the current compensation link in the mode smooth switching is designed.The application scope and feasibility of the control strategy are verified by Simulink.