Large-Signal Stability Analysis of MMC-HVDC System Under Grid Voltage Dips Based on Mixed Potential Theory

Abstract

Modular multilevel converters (MMCs) are widely used in high voltage direct current (HVDC) transmission systems due to their superior performance. However, when modular multilevel converter based high voltage direct current (MMC-HVDC) system become unstable under the large-signal disturbance of grid voltage dips, the small-signal analysis method would be no longer available. In this paper, the large-signal stability of MMC-HVDC system under grid voltage dips is studied based on mixed potential theory. First, a simplified state-space averaging model of MMC-HVDC system is established. Furthermore, the large-signal stability criterion is obtained by using the mixed potential theory and the system large-signal stability working area is delineated. Then, the influence of system parameters and the degree of grid voltage dips on the large-signal stability is studied. Finally, aiming at the unstable situation, a solution to adjust the system parameters and control parameters is proposed based on the large-signal stability criterion. Time-domain simulations conducted in Matlab/Simulink are used to verify the effectiveness and accuracy of the large-signal stability analysis method.