Research On Control Strategy Of Parallel Inverter

In recent years,with the rapid development of the economy,the demand for electricity in society has increased.Microgrid has received a lot of attention as a new type of power generation system.As the core converter device in the microgrid system,the inverter selects an effective control strategy,which has a decisive influence on ensuring the safety,stability and output of high quality electric energy of the entire microgrid system.Most distributed microgrid power generation systems are geographically dispersed,operating in island mode or as part of a larger grid.Therefore,it is of great and far-reaching significance to study the control strategy of the inverter in the microgrid system.In the microgrid system,the lines exhibit different impedance characteristics,and different impedance characteristics affect the selection of the inverter droop control strategy.By analyzing the characteristics of the equivalent output impedance of the inverter,the virtual complex impedance is introduced on the basis of the traditional droop control strategy,and the equivalent output impedance of the inverter is improved by adjusting the virtual parameters.Make each inverter have better power decoupling effect.By analyzing the relationship between the circulating current between the parallel inverters and the equivalent output impedance of the inverter,it is proved by simulation experiments that the droop control strategy that introduces the virtual complex impedance can not only reduce the circulation between the parallel inverters,but also make the inverse The power output of the transformer is more stable and has a better equalization effect.In a microgrid system,the inverter is connected to the load through different lines.The difference in line impedance causes different voltage drops on each line of the inverter,consuming different powers,resulting in an imbalance in the output power of the inverter.In this paper,two inverters with the same capacity are studied.By analyzing the cause of the voltagedrop,a PI equalization controller is introduced in the traditional reactive power droop control,which makes it possible to adaptively adjust the droop coefficient and automatically track the average reactive power to achieve reactive power sharing.And combined with the traditional active power droop control into an improved droop control strategy,the parallel inverter with the same capacity can achieve power sharing even when the line impedance is different.Based on the advantages of the integrated virtual complex impedance method and the improved droop controller method,an improved droop control method with virtual complex impedance is proposed.The simulation experiment is established.By analyzing the circulation diagram between the parallel inverters and the output power diagram of the inverter,it is verified that the improved droop control method with virtual complex impedance is not only able to reduce the parallel inverter in the microgrid with different line impedance.The circulation between the devices can also achieve power sharing between the parallel inverters.