Analysis On Interactive Influences Among Multiple Parallel Three-phase Inverters Based On Frequency Domain RGA Principle

Three-phase grid-connected inverter is an important part of AC / DC hybrid microgrid,which plays an important role in the reliable and stable operation of the system.As a bridge between distributed generation system and power grid,the redundancy design of parallel inverters provides an effective solution for large-scale distributed generation.In order to solve the problem of interaction among three-phase grid-connected inverters,which are mostly used in the multi-inverter grid-connected system and have relatively complex control structure,the frequency based relative gain array principle is used to analyze the degree of interaction between multiple three-phase grid-connected inverters quantitatively.And it can provide experience for optimal design of inverter control system and improvement of power quality of parallel inverter system.The relevant conclusions are as follows:Firstly,the research status and development trend of microgrid are introduced,including AC microgrid,DC microgrid and AC DC hybrid microgrid.The research status of parallel operation control strategy of three-phase inverter and the interaction effect between parallel inverters are summarized.The types of filters and related damping schemes in multiple threephase inverters grid-connected system are determined.The types of common filters are briefly introduced.The frequency characteristic curve and corresponding power loss of common passive damping schemes are described.Combined with their advantages and disadvantages,an active damping scheme of LCL filter based on capacitive current feedback is proposed.Secondly,based on the multiple LCL three-phase inverter grid-connected system structure,the overall control strategy of parallel operation is designed,including droop control,voltage and current double closed loop PR control and active damping control based on capacitor current feedback.The simulation results in Matlab/Simulink verify the correctness and effectiveness of the proposed overall control system.Thirdly,based on the principle of relative gain array in frequency domain,a quantitative analysis method of interaction degree between parallel three-phase inverters is proposed.Considering the nonlinear factors,the Norton equivalent model of the multiple LCL three-phase inverter grid-connected system in α-β coordinate is derived,and the relative gain array of the system is obtained by combining with the principle of relative gain array.Based on the elements in the array,the interaction between parallel inverters is quantitatively analyzed in details,which is related to the change of system operation mode,number of parallel inverters,system hardware parameters and system control parameters.The simulation results in Matlab/Simulink verify the effectiveness of the proposed quantitative analysis method of interaction degree between parallel three-phase inverters.Finally,the experimental platform of multiple three-phase inverter grid-connected system is built on d SPACE hardware in the loop simulation platform,and the experimental results are the same as the simulation results,which shows that the relative gain array principle based on frequency domain can effectively quantitatively analyze the interaction between parallel threephase inverters.