Research On Control Strategy Of Parallel Operation Of Microgrid Inverter

With the continuous improvement of power levels in microgrid systems,a single inverter can no longer meet high-power and large-capacity applications.At this time,the parallel connection of micro-grid inverters has become the key technology to solve the problem,which not only expands the system capacity but also has flexibility.The parallel mode of inverter can be divided into independent DC bus and common DC bus,but either structure will bring the problem of circulation.The circulating current will affect the current quality of the system output,and even damage the system in severe cases.Therefore,this paper focuses on the in-depth research on the circulating current of the microgrid,mainly including the following aspects:（1）In this paper,the circulation generated by parallel inverters was taken as the research object,and the basic structure of a single microgrid inverter is established in order to suppress the circulation.Then,the mechanism of circulation generated by parallel inverters was analyzed,and the voltage and current double closed-loop control strategy was designed.（2）Aiming at the problem of circulating current caused by uneven power distribution in the independent DC bus parallel inverter structure,a control strategy combined with linear active disturbance rejection technology was proposed based on the analysis of the inherent defects of power distribution and voltage deviation in traditional droop control.The linear expansion state observer was used to compensate unknown disturbances such as parameter imbalance to maintain the consistent voltage amplitude of the output of the parallel inverter.Then the power equalization and circulation reduction can be achieved by adjusting the appropriate controller parameters.（3）At the same time,a zero-sequence circulation controller was designed to solve the zero-sequence circulation current loss caused by the common DC bus parallel inverter structure,and an improved linear active disturbance rejection control strategy was proposed.The controller increases the compensation of total disturbance estimation error in error feedback control and improves the performance of the controller.Thus,an accurate zero vector distribution factor can be obtained to regulate duty cycle,which can eliminate the difference between inverters and suppress the zero sequence circulating current.（4）Finally,this paper builds two parallel inverter structure models on the Matlab/Simulink simulation platform,and verifies the effect of linear active disturbance rejection control technology in circulating current suppression under various operating conditions,and achieves the purpose of circulating current suppression.Then it effectively improves the parallel operation ability of microgrid inverter.