Research On Power Sharing And Pre-synchronization Control Of Microgrid

Economic development has brought the serious energy shortages and environmental problems,widely used in the clean pollution-free renewable energy to become the development trend of future energy,solar energy,wind energy to generate power of distributed power generation technology by more and more people's attention,but because of the influence of factors such as geography,climate,solar and wind power electricity vulnerable to fluctuations in the output,directly connected to the power grid may reduce its power grid power quality.In order to fully develop distributed power generation and solve its adverse effects,micro-grid technology emerges at the right moment.The stable operation of microgrid cannot be separated from good control mode,and the control of microgrid is mainly reflected in the control of microgrid inverter.Based on micro power grid three-phase inverter as the research object,on the inverter control strategy choice droop control method in the micro containing multiple distributed power grid,according to the traditional droop control output characteristic curve were analyzed,and the data suggest that active power system can be carried out in accordance with the proportion of distributed power supply capacity allocation,but due to the voltage of the inverter output will be affected due to the different of line impedance,and affect the inverter capacity according to the proportion of output reactive power,and the micro inverter application droop control makes the bus voltage amplitude and frequency is reduced,and the power grid voltage exists certain deviation.It is hoped that based on the traditional droop control and by improving the control strategy of the inverter,the reactive power of the system can be reasonably distributed under the condition of arbitrary line impedance,and the control goal of smooth grid-connection of the microgrid can be achieved according to the needs.In this paper,two operating modes of microgrid,island and grid-connection,control strategies of microgrid and three control strategies of microgrid inverter are introduced.The mathematical model of three-phase inverter is established and the simulation analysis of single inverter is carried out on the basis of traditional droopcontrol.Then,the mechanism of active power and reactive power distribution in the micro grid with two inverters in parallel is analyzed,and the factors affecting the rational distribution of reactive power and the limitations of traditional droop control are obtained.Next,the principle of virtual impedance method is introduced.By adding virtual impedance link into the inverter,the negative effect of traditional droop control is reduced.However,the virtual impedance with fixed resistance value still cannot eliminate the reactive power distribution error in the system.Later,on the basis of the proposed adaptive virtual impedance control method and its mathematical model is set up,by add amount of reactive power in active droop equations of active power variation,which is obtained by feedback adaptive virtual impedance value,ultimately achieve accurate distribution of reactive power,eliminate the error of reactive power distribution.In addition,because of the sagging control inverter can cause loss of busbar voltage amplitude and frequency of makes and outlets of reach grid voltage requirements,this article collected by double phase lock loop and network and the information of the power grid voltage,on the amplitude and phase synchronization control strategy to achieve smooth micro power grid interconnection control targets,and finally,in the Matlab/Simulink simulation verifies the correctness of this control strategy.