Research On Microgrid Droop Control Strategy Based On Virtual Impedance

Since the 21st century,Based on distributed generation,microgrid has attracted the attention of the international scholars because of its small size and strong flexibility.Therefore,inverter control technology is very important for microgrid to maintain high stability and power quality.In this paper,the control strategy of parallel inverters in low-voltage microgrid under island mode is studied.Among the control strategies for microgrid inverters,peer-to-peer control can automatically adjust the frequency and amplitude of the output voltage of the inverters according to the system load,which has high flexibility.Droop control strategy is one of the typical control strategies.However,the traditional inductive droop control strategy cannot meet the operation requirements of low-voltage microgrid.In order to make the droop control strategy further applicable to low-voltage microgrid,this paper adopts the resistive droop control strategy to make it more compatible with low-voltage microgrid.In the practical application of microgrid,due to the large difference in line impedance between each distributed generation and the main grid,the system cannot meet the conditions of reasonable load distribution.This paper introduces an adaptive virtual resistance on the basis of the traditional virtual impedance.This control strategy enables the virtual resistance to change according to the system operation situation in real time and carry on the track to the bus voltage at the same time,which can compensate the bus voltage to to some extent.Due to the inherent characteristics of resistive droop control strategy,when the output active power of each inverter exceeds the rated capacity,the amplitude of output voltage of the inverter will appear larger bus voltage drop.Moreover,the compensation effect of the adaptive virtual resistance is not obvious at this time.Therefore,a bus voltage compensation strategy is adopted in this paper.Firstly,the traditional resistive droop characteristic curve is combined with exponential function to reduce the voltage drop amplitude and ensure the voltage does not exceed the limit.Secondly,a bus voltage compensation strategy based on PI control is introduced,which can compensate the voltage drop caused by virtual resistance.Finally,the system is modeled and simulated on the simulation platform.The results show that when the line impedance is different and the system load changes,the improved control strategy adopted in this paper can not only make the load distribution more reasonable,but also compensate the bus voltage greatly,and the improvement effect is remarkable.