Analysis of Small-Disturbance Stability of Onshore Wind Power All-DC Power Generation System and Identification of Leading Factors

The application of conventional AC collection for the integration of large-scale renewable energy sources may lead to issues concerning harmonic resonance and reactive power transmission. Conversely, the utilization of an all-DC power generation system for wind power (WDCG) can effectively circumvent such issues. In contrast to the conventional power system, the interdependence among subsystems in the WDCG renders it susceptible to oscillation instability in the presence of minor disturbances. To address this concern, this paper first establishes a small-signal model for the WDCG, and validates the accuracy of this model by comparing it with an electromagnetic transient model based on PSCAD/EMTDC. Secondly, employing the eigenvalue analysis method, the principal oscillation modes of the WDCG are identified, and the state variables strongly correlated with these modes are analyzed using the participation factor method. Moreover, a quantitative assessment of the impact of operational and control parameters closely associated with the strongly correlated state variables on the negative damper oscillation model is conducted. The findings of the analysis reveal that the small-disturbance stability of the WDCG is significantly influenced by the operational parameters of the outlet capacitance of the ma-chine-side converter (MSC), the outlet capacitance of the direct current wind turbine (DCWT), the sub-module capacitance of the modular multilevel converter (MMC), and the inductance of the bridge arm. Additionally, the stability is al-so affected by the control parameters of the constant DC voltage control on the DCWT side, the voltage outer-loop-current inner-loop control, and the circulation suppression on the MMC side. The simulation results based on PSCAD validate the efficacy of the proposed method in identifying the dominant factors.