Study On Drop Control Strategy Of Low Voltage Microgrid Inverter Based On Virtual Impedance

In recent years,due to the shortage of fossil energy and the rapid growth of electricity demand,microgrid technology based on distributed generation technology is more widely used in power system.The distributed power in microgrid mostly makes the inverter as an interface converter,and the access of multiple distribute power forms multi-inverter parallel environment in microgrid.As the main control method of parallel microgrid inverter,the droop control can realize reasonable power distribution without communication lines,and has the advantage of high redundancy.However,the traditional droop control is realized based on the inductive characteristics of the line under high voltage conditions.It is difficult to achieve a reasonable distribution of output power by parallel inverter transmission in the low voltage microgrid.Therefore,thesis analysis the power distribution and voltage stability of parallel inverters with droop control in low voltage microgrid.Firstly,the three-phase inverter was taken as the research object.On the basis of the analysis of mathematical model and structure of the three-phase inverter,the voltage and current double-loop control parameters and filtering parameters are analyzed,and the Inverter with having different impedance characteristics is realized by changing the control parameters.Secondly,according to the power transmission characteristics of the inverter,the type and application range of the droop control are discussed.In addition,the conditions for accurate power distribution between parallel inverters under low-voltage microgrid are studied,and the correctness of droop control and power allocation conditions is verified by simulation.Thirdly,because the output power of parallel inverters is correlated with the line impedance,an improved control strategy based on virtual impedance was proposed and the principle and method of virtual impedance were analyzed.To solve the voltage sag problem caused by virtual impedance control strategy,a control method based on output voltage amplitude feedback is proposed,which effectively improves the power quality of parallel system by extending the amplitude of the output voltage before the introduction of virtual impedance.In order to further improve the output power allocation accuracy of parallel inverters,an adaptive virtual impedance control strategy is proposed,which introduces a integral control link into the virtual impedance,and adaptively adjusts the virtual impedance by power information to achieve accurate power distribution.Finally,the simulation model is built by Matlab software,and the result showed the accuracy of the proposed voltage amplitude feedback control strategy and adaptive virtual impedance control strategy.