基于零序环流控制器的海上风电MMC-HVDC并网系统小干扰稳定分析与优化控制

Small Signal Stability Analysis and Optimization Control of Offshore Wind Power Generation MMC-HVDC Grid-connected System Based on Zero-sequence Circulating Current Controller

基于模块化多电平换流器(modular multilevel converter,MMC)的高压直流(high voltage direct current,HVDC)输电技术广泛应用于海上风电并网工程,并网系统的小干扰稳定性问题一直备受关注。文中围绕MMC零序环流控制器对海上风电MMC-HVDC并网系统稳定性的影响展开研究,首先采用复矢量和谐波状态空间的方法建立MMC闭环频域模型,进而推导出考虑零序环流控制器的MMC单输入单输出阻抗模型,其次建立海上风电与集线网络阻抗模型。基于以上模型探究零序环流控制器对并网系统稳定性的影响规律及作用机理。分析结果表明,海上风电场出力过大时,系统易出现振荡风险;零序环流控制器的投入等效增大了桥臂电阻,增强了系统阻尼,能够有效抑制孤岛控制模式下MMC的阻抗谐振峰值。最后,从增强系统阻尼的角度设计零序环流控制器参数优化方案,通过仿真验证理论的正确性和方案的可行性。

The high voltage direct current(HVDC) transmission technology based on modular multilevel converter(MMC) is widely used in the offshore grid-connected wind power generation projects. Small signal stability problems of the grid-connected system have been attracted great attention. This paper focused on the influence of the zero-sequence circulating current(ZSCC) controller on the stability of the offshore wind power generation MMC-HVDC grid-connected system. The closed-loop frequency domain model was derived by means of complex vectors and harmonic state space firstly. Then the paper developed the single-input-single-output(SISO) impedance model of MMC which considering the ZSCC controller. In addition, the impedance model of the offshore wind farm and the distribution network were established. Based on the impedance model, the influence law and mechanism of the ZSCC controller on the stability of the offshore wind power generation MMC-HVDC grid-connected system were explored. The analysis results show that when the output power of wind is too large, the system is prone to oscillation. The application of the ZSCC controller equivalently increases the bridge arm resistance and enhancing the system damping, which effectively suppressing the resonant peaks of MMC impedance in island control mode. Finally, from the point of view of enhancing the damping of the system, the parameter optimization scheme for ZSCC controller was designed, and the correctness of the theory and the feasibility of the scheme were verified by simulations.