Research On Multiple Micro-source Coordination Control Strategy Of Low Voltage Microgrid

Microgrid is a small power generation,distribution and consumption system that integrates distributed power supplies,energy storage devices,energy conversion devices,control devices,monitoring and protection devices with energy transmission lines and loads.The distributed power supply in the microgrid is connected to the grid through the inverter device,and making full use of the advantages of the distributed power supply and the flexible controllability of the inverter device can lay a foundation for improving the power quality of the microgrid system.In the low voltage microgrid,the droop control is used to control the voltage drop when the power distribution of the micro-source inverter is realized.How to realize the equalization control of the inverter power and the stability of the voltage stabilization becomes the key problem of the stable operation of the low voltage microgrid.Therefore,this paper studies the droop control strategy based on virtual impedance.On this basis,the hierarchical coordination control strategy is used to improve the equalization control of inverter power sharing and voltage stability.Firstly,the paper has studied the common control strategy of microgrid and the control method commonly used in microgrid interface inverter.The mathematical model of wind turbine,photovoltaic cell,battery energy storage unit and fuel cell is established.And the output characteristics of the distributed generation unit are simulated by MATLAB/Simulink.Secondly,the paper analyzing the power transmission characteristics of inverter,designing power controller and devising loop controller of voltage and current.In order to solve the problems about the precise distribution of inverter's output power and balanced control of stable voltage,the thesis has proposed an improved droop control strategy.By introducing virtual impedance control loop,it can realize power decoupling and improve the power output accuracy of the inverter and voltage stability.Thirdly,in order to solve the problem of the voltage drop of the microgrid system,which is caused by the delay of the micro-source inverter and the slow response of the micro-source inverter during the transition period of the island,the paper has improved the measurement of energy storage battery and the power control loop of fuel cell and energy storage battery and has proposed the multi-micro-source coordinated control strategy of microgrid based on hierarchical control to ensure system transient stability.Finally,the control strategy of microgrid operation based on hierarchical control and islanding mode is simulated by MATLAB/Simulink simulation software.The simulation results show that the improved droop control strategy based on virtual impedance has a good control effect on the equalization control of power precise distribution and voltage stability,which is of great significance to the transient stability and power quality improvement of low voltage microgrid system.