Research On Power Control Strategy Of Multiinverter In Microgrid

Inverter parallel control technology is one of the key technologies to achieve the expansion of micro-grid,improve the power quality and ensure stable operation of the micro-grid,so it is very necessary to conduct research on this technology.Aiming at the influence of line impedance difference in parallel inverter system on the power sharing accuracy of the system,an improved robust droop power control strategy is proposed and studied in this paper.It can effectively improve the system power sharing accuracy and suppress the circulating current in the case of large difference in line impedance.At the same time,it has good dynamic performance.The main research contents and outcomes completed in this paper are as follows:(1)Based on the analysis of several classical control methods for independent operation of the inverter,the methods of double-loop PI control and repeated control are selected for detailed study,and the models of double-loop PI control inverter system and repeated control inverter system are established.Carrying out simulation and comparative analysis,a composite control method based on double-loop PI control and repeated control has been proposed.Through the simulation experiment,the conclusion is drawn: the composite control method performs better than the single double-loop PI control and repeat control.(2)Based on the analysis of equivalent circuit model of parallel inverter system,power droop control principle and system circulation characteristics,the model of parallel inverter system is established by using composite control method and droop power control strategy which the equivalent output impedance is resistive.And it has been carried on the simulation research under the environment of MATLAB/Simulink.Conclusion: the power droop control strategy in which the equivalent output impedance of inverter is resistive can realize the system power sharing,but larger in line impedance difference and output voltage,power sharing accuracy of system will be affected,and even lead to system instability.(3)For the problem that the line impedance and output voltage difference of the parallel inverter system affect the system power sharing accuracy and the circulating current,an improved robust droop power control strategy has been proposed based on the conventional droop power control strategy.Firstly,based on the research on the adaptive virtual impedance link,the integral link in the active power loop and the voltage initial value link,an improved droop power controller model is established.Secondly,doing a simulation analysis of improved robust droop power control strategy and conventional robust droop power control strategy in the MATLAB/Simulink module.The results verify that the improved method has higher power sharing accuracy and circulation suppression capability than conventional methods,especially in the dynamic response performance,the transition can be completed in a shorter time and the power fluctuation is smaller.It proves the effectiveness of the strategy proposed in this paper.The difference in line impedance of the parallel inverter system will increase the voltage amplitude and phase difference between the inverter units.The proposed method can effectively reduce the influence of these differences on the system power sharing accuracy and circulating current,and has good dynamic performance and steady state performance.