Research On Improved Droop Control Of Wind-solar Storage Microgrid Based On Virtual Impedance

With the continuous progress of science,technology and social economy,the use of renewable energy becomes more and more important,so distributed generation technology emerges as the times require.However,distributed generation technology also has many drawbacks in control and crisis management.In order to solve these problems,the concept of microgrid has been proposed.As the most important part of the micro-grid structure,the control of inverters is related to the safety and stability of the micro-grid.In view of the current energy demand and scientific and technological hotspots,it is of great significance and value to develop the control method of inverters for wind,solar and storage microgrids in off-grid state.The main contents of this paper are as follows:Firstly,the classification and characteristics of microgrids with different structures are introduced,and three control methods commonly used in inverters are briefly analyzed.According to the data access and the analysis of the three control methods,the shortcomings are pointed out.Secondly,the working principles of wind power generation system,photovoltaic array and storage battery are deeply analyzed.The mathematical models of the three distributed generators are established,and the simulation models of the three distributed generators are built in Simulink.Based on the established simulation model,the disturbance observation method with duty cycle disturbance is used to control the power of wind turbine.The output power of photovoltaic power generation system is controlled by disturbance observation method with voltage as disturbance.The charging and discharging control of storage battery is realized by bidirectional DC/DC power converter.The constant voltage charging method is adopted in battery charging,which realizes faster charging at the initial stage of charging,and reduces charging current at the later stage of charging,so as to protect the battery.The maximum power tracking control of wind power generation and photovoltaic power generation uses S function to build S imulink model,while the control of storage battery is a double closed-loop control of voltage and current built directly in S imulink.The simulation experiments of the above control methods are carried out.Finally,the power output characteristics of microgrid inverters are analyzed.In view of the weak coupling between the active and reactive components of the output power of the inverters and the disadvantage that the traditional droop control method is only applicable to the high voltage power grid,an improved droop control method based on virtual impedance is proposed.A simulation model of off-grid operation of microgrid is established in Simulink with wind-solar storage as distributed power supply,and the simulation experiment of this inverter control method is carried out.The simulation results verify the feasibility and effectiveness of the proposed method.