构网型柔性直流换流站低频段振荡分析及抑制策略OA

The grid-forming flexible DC converter stations based on the single closed-loop voltage control exhibit excellent voltage support capability for the AC power grid.However,it faces a high risk of oscillation in the low-frequency power range(0～100 Hz),especially in the near-fundamental frequency band(46～54 Hz).Firstly,a detailed theoretical analysis model of the flexible DC converter station is established,the open-loop transfer function of the power angle at the point of common coupling is derived,the generation mechanisms of power oscillations in the near-fundamental frequency and low-frequency ranges are revealed,and corresponding suppression principles are proposed.Secondly,targeting the two types of oscillation risks,a low-frequency damping control strategy is proposed,and the influence of this strategy on the power angle open-loop transfer function and low-frequency impedance is analyzed.The results show that the impedance provided by the damping controller can be separated from the original impedance of the modular multilevel converter into an additive analytical expression.On this basis,a parameter design method for compensating the integral area of negative damping in the low-frequency range is proposed,and the analytical selection range of parameters is given.Finally,the correctness of the proposed model and damping control strategy is verified through both theoretical analysis and electromagnetic transient simulations.