MMC-交 直流混合导纳建模及交直流耦合作用下的并网系统稳定性分析

With the advent of new energy power generation systems, the flexible DC transmission system is expanding rapidly， but the wide-band oscillation has posed a serious threat. The modular multilevel converter (MMC) is the key device in flexible DC transmission, and its admittance model is the basis of the system stability analysis. Considering the coupling effect of AC/DC systems, based on the harmonic state-space method, this manuscript proposes the hybrid AC/DC admittance model and realizes the accurate characterization of self-admittance and coupling admittance. Secondly, a wide-band oscillation analysis method for the MMC grid-tied system is proposed based on the hybrid AC/DC admittance model and schur matrix transformation theory. The proposed method can analyze the system's stability compared with traditional methods. At the same time, it can explicitly characterize the influence of stability on AC systems and DC systems and the coupling interaction between AC and DC systems. What’s more, it can effectively distinguish different causes of system instability, and reveal the mechanism of wide-band oscillation of grid-tied systems induced by coupling between AC and DC systems. Finally, by comparing with MATLAB/Simulink simulation results, the accuracy of the hybrid AC/DC admittance model, its advantage for grid-tied system stability analysis, and the correctness of the system stability analysis are verified.