The Research On Power Regulation Of Parallel Inverters In Microgrid Based On Virtual Impedance

With the rapid development of economic and social productivity,people’s consumption of energy has increased sharply.In order to protect the environment and achieve sustainable development of energy,renewable energy based on solar energy and wind energy has gradually attracted everyone’s attention.Distributed generation opens up new directions for the utilization of various renewable energy,but distributed generation is random,which will bring many problems to the grid connection of distributed generation.The proposal of microgrid can well solve the problem of distributed generation,and can effectively improve the utilization efficiency of renewable energy and optimize the energy structure.The droop control method is a commonly used control method for microgrid inverters.It can be used in grid-connected and islanded states.Therefore,this paper studies the problems of the microgrid parallel inverter system based on the droop control method.At first,the line impedance of the microgrid is usually resistive and inductive,which makes the power coupling problem in the control process.In this paper,the equivalent output impedance of the inverter is made inductive by introducing virtual inductance feedback control,which greatly improves the accuracy of power decoupling control in inductive droop control.Secondly,when high-power load switching occurs in the microgrid,due to the automatic adjustment of the droop control method,it is likely that the output voltage and frequency of the inverter will exceed the normal range,which will seriously affect the power quality.In this paper,a segmented curve droop control strategy is proposed.According to the conditions satisfied by the segmented curve droop control strategy,the general expression of the segmented droop curve is obtained,and a mathematical method is used to prove the logarithmic function segmented curve droop control.Compared with other types of curve control in power distribution,it can ensure that the voltage and frequency output by the inverter are always within the normal range,and the power quality of the grid can be guaranteed.Finally,the geographical distribution of the distributed generations in the microgrid are random,which leads to the fact that the impedance of each line is not equal,so that the power output by each parallel inverter cannot be reasonably distributed according to its droop coefficient,which will lead to serious system circulation and affect the stable operation of the microgrid.This paper proposes an adaptive virtual impedance control method.The virtual impedance value is obtained by multiplying the ratio of the reactive power value to the voltage amplitude value by the virtual impedance coefficient,which can effectively improve the equalization accuracy of the output power of the parallel inverter.By comparing the Bode diagrams before and after adding the virtual inductor,it is proved that the virtual inductor method can improve the power decoupling control effect.The control effect of the segmented curve droop control strategy in this paper is verified by simulation comparison.The effect of the method in reducing the reactive power sharing error is verified by detailed simulation and experimental comparison.