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Stability studies of voltage-source converter HVDC (VSC-HVDC) systems are mainly based on small-signal linearization techniques. However, when VSC-HVDC systems become unstable due to large-signal disturbances, the small-signal analysis method would be no longer available. In this paper, the large signal stability of VSC-HVDC system is studied based on mixed potential theory. A simplified state-space averaging model of VSC-HVDC system is established under the synchronous rotating reference frame. Based on this model, the stability prediction criteria for VSC-HVDC system under large-signal disturbances is obtained through Brayton-Moser's nonlinear potential method. On this foundation, the influence of system parameters on the large-signal stability is studied and the boundaries of stability are located as well. Time-domain simulations conducted in Matlab/Simulink are used to test the stability of the working points next to the stable boundary, which aim to prove the correctness of the obtained stability criterion. Aiming at the unstable situation, the time-domain simulation results prove the feasibility of the method of adjusting the system parameters according to the stability criterion to make the system stable, which further verifies the correctness of the stability criterion. [ABSTRACT FROM AUTHOR]

The existing research on voltage-source converter HVDC (VSC-HVDC) system stability mostly focuses on small-signal stability analysis methods. However, when large-signal disturbances occur, the intrinsic nonlinearity of the VSC-HVDC system becomes inevitable so that the small-signal studies are no longer valid. In this paper, a large-signal stability analysis method of the VSC-HVDC system is proposed based on the estimation of domain of attraction (DOA). This method can not only analyze the asymptotic stability of the operating point, but also answer the question of how large deviations from the operating point can be tolerated by the system. By using Takagi-Sugeno (T-S) fuzzy model and Lyapunov stability theorem, the DOA of the VSC-HVDC System at the operating point is estimated, and the large-signal stability of VSC-HVDC System is analyzed. On this foundation, the influence of system parameters on the large-signal stability is studied. The results can be used to guide the adjustment of system parameters to solve the problem of system instability. The time-domain simulations conducted in Matlab/Simulink are used to test the stability of the system under large-signal disturbance in the range of DOA. The simulation results verify the feasibility and effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]