Research On Power Distribution Strategy Of Parallel Operation Of Inverters Based On VSG

As the installed capacity of renewable energy continues to expand,distributed power sources need to use multiple inverters in parallel to improve the capacity and reliability of the microgrid system.The traditional inverter control does not have inertia and damping characteristics,and the stabi lity of the grid system is easily affected by the power electronic converter,so the traditional inverter control loses its advantages.VSG control is based on the traditional inverter control,with inertia link and damping characteristic link.When the microgrid is running off-grid,the application of VSG control can improve the stability of power supply from multiple distributed power sources to electric loads.Therefore,it is very important to study the inverter parallel control strategy with VSG control as the core.This paper is mainly to study the output power distribution strategy of the VSG inverter parallel system in the off-grid mode,aiming at the coupling between the active and reactive power of the inverter output under the low-voltage microgrid and the line impedance mismatch caused by the inverter capacity For the problem that the reactive power cannot be divided equally,the virtual complex impedance control is adaptively improved,and the adaptive virtual impedance control strategy is adopted to improve the reactive power distribution accuracy,and the common bus voltage drop is small.The main research contents are as follows:(1)Establish a three-phase power inverter analysis model based on the dq coordinate system,design the parameters of the LC filter and the voltage and current double closed-loop control parameters after introducing compensation,and draw the voltage and current double closed-loop transfer function after the compensation link is introduced.Bode diagram,verify that the double closed loop has good control performance.(2)Combined with the model principle of the synchronous generator,the power frequency controller and excitation controller of the VSG are studied.Explore the selection principles of several important parameters of VSG and their influence on the stable operation of the system.The VSG model is simulated,and the simulation results are used to study and analyze how the important parameters of the VSG affect the control performance of the power frequency converter and the exciter.(3)Study the uniform distribution conditions of the output power of the VSG control system.For the coupling between the output active and reactive power under the low-voltage microgrid,and the line impedance mismatch caused by the inverter capacity,the power cannot be divided equally,and the virtual complex impedance control is introduced.Decoupling of power and matching the line impedance to the inverter capacity improves the accuracy of output power distribution.Using Matlab/Simulink to establish a simulation model of virtual complex impedance control for research and analysis,the simulation results show that although the introduction of virtual complex impedance can improve the accuracy of reactive power distribution,it also causes a serious drop in bus voltage.(4)In order to further improve the accuracy of reactive power distribution and reduce the bus voltage drop,the virtual complex impedance control is adaptively improved,and the adaptive virtual impedance control strategy is adopted to adaptively adjust the equivalent output impedance in the system to accurately match the output impedance.The inverter capacity improves the accuracy of reactive power sharing,and alleviates the contradictory relationship between the accuracy of reactive power distribution and the quality of bus voltage and power.The system simulation model based on the adaptive virtual impedance control strategy under different working conditions is established.The simulation results show that the improved control strategy improves the precision of reactive power sharing and the common bus voltage drop is smaller.