Quantitative Analysis Method Based on Frequency Domain RGA for Coupling Degree of Parallel Converters

When LCL-type converters operate in parallel to increase system transmission capacity, the coupling will be generated by the difference of parameters, synchronization control and the change of grid impedance, which will reduce the cohesiveness of a single converter. The coupling analysis method based on the relative gain array (RGA) in the frequency domain is proposed in this paper to reveal the coupling mechanism of parallel converters. The transfer function model of the LCL-type converter with an active damping control loop is established. A high-order network matrix under multi-machine operating conditions is constructed based on the analysis of the impedance characteristics of a single converter. Combined with the principle of relative gain, the RGA model of parallel converters is established. And the main risk factors affecting the coupling characteristics of the parallel converter are quantitatively analyzed. Finally, the proposed analysis method is validated by simulation and experimental analysis. The proposed analytical method that can quantitatively analyze the coupling degree and reveal the coupling mechanism of parallel converters, which provides a theoretical basis for the optimization of the software and hardware parameters.