An admittance-reshaping control method for improving the stability of multi-parallel grid-connected converters

The interaction amomg multi-parallel grid-connected converters (MPGCC) in weak grid often leads to stability challenges. This paper presents a converter admittance-reshaping control method designed to improve the stability of the MPGCC system. Firstly, a generalized mathematical model of a three-phase MPGCC system, which incorporates the interaction between converters, is established and the small-signal model is emplogyed for analysis. It reveals that kdq1(s) and kdq2(s) must satisfy the Nyquist criterion in a MPGCC system, where kdq1(s) represents the series interaction between the main grid and the MPGCC system, and kdq2(s) represents the interaction amomg the converters. Considering the uniqueness of stability analysis for MPGCC systems, this study integrates admittance reshaping-matrices into the control structure of the converters using the positive real method. This approach ensures that both the output admittance matrix of the converter and its inverse matrix are strictly positive real, thereby achieving passivity in the two-dimensional admittance model of the three-phase MPGCC output. This theoretically guarantees the asymptotic stability of the MPGCC system, thereby improving system stability. Finally, simulations and experimental tests are conducted on a device omprising three parallel-connected grid-connected converters to validate the effectiveness of the proposed control method. This paper is accompanied by a video that demonstrates the validation results.