Research On Micro-grid Inverter Control Strategy Based On Improved Droop Control

Under the dual pressures of energy demand and environmental protection,the micro-grid that makes full use of new energy to generate electricity has received more and more attention.Droop control is an important control strategy in micro-grid.It can improve the stability,safety and reliability of the micro-grid during islanding and grid-connected operation.However,this control strategy is still subject to interference from different line impedance characteristics and harmonics,and will cause deviations in the bus voltage.This topic is mainly aimed at timproving he shortcomings of traditional droop control strategies in low-voltage micro-grids.For the problem of distributed generation output coupling of traditional droop control in low voltage micro-grid,a mathematical model of the inverter with droop control is established in the dq coord:inate system.Combined with the comprehensive analysis results of the distributed generation transmission characteristics and the droop curve,a virtual impedance is added to the control strategy.At the same time,the influence of the virtual impedance control loop on the output characteristics of the system is analyzed.The voltage-current dual-loop controller and the virtual impedance droop control model of the control strategy are designed.And the micro-grid model was established in MATLAB/Simulink to verify the effectiveness of the improved droop control method.Due to the existence of a large number of power electronic devices and non-linear loads in the micro-grid,the distributed generation output voltage is affected by harmonics.A second-order generalized integrator is added to the virtual impedance loop to suppress harmonics.And the droop control model based on second-order generalized integral virtual impedance is established.The simulation results of the micro-grid isolated and grid-connected harmonic suppression are carried out.The results show that the method can effectively suppress harmonics,and the larger the value of virtual impedance,the better the harmonic suppression ability.For problem of the bus voltage deviation caused by the virtual impedance droop control strategy during use,the system voltage is too low.Based on the second-order generalized integral virtual impedance droop control,the voltage deviation real-time calculation compensation link is added.Through the simulation study of the voltage compensation method,the results show that the bus voltage can be kept at the rated value during the whole operation of the micro-grid,thus avoiding the adverse effect of the bus voltage deviation on the micro-grid system.