一种适用于MMC-HVDC联接弱受端交流电网的附加频率–电压阻尼控制方法

A Supplementary Frequency-voltage Damping Control for MMC-HVDC System Connected to Weak AC Grid

提出一种新型附加频率–电压阻尼控制（supplementary frequency-voltage damping control,SFVDC）,可以有效改善联接弱受端交流系统的模块化多电平换流器直流输电（modular multilevel converter based HVDC,MMC-HVDC）的小干扰稳定性。该控制方法基于锁相环的输出角频率和引入的阻尼系数,产生交流电压的附加阻尼分量,用以抑制由于交流系统强度低而导致的系统小干扰失稳现象。首先建立了包含SFVDC在内的MMC系统的详细小干扰模型,并与PSCAD/EMTDC中的电磁暂态仿真结果进行对比,验证了模型的正确性。然后采用特征根分析法研究了阻尼系数对MMC系统小干扰稳定性的影响及其在不同短路比下的可行范围。最后,针对交流系统频率变化,研究了SFVDC控制下MMC系统的动态特性。结果表明,SFVDC控制可以有效抑制MMC联接弱系统时出现的小干扰不稳定现象,明显改善了系统的稳定性。

A supplementary frequency-voltage damping control（SFVDC） was proposed to improve the small-signal stability of modular multilevel converter based HVDC（MMC-HVDC） system under weak AC grid conditions. Based on the output frequency from phase-locked loop（PLL）, the SFVDC approach introduced a damping coefficient and then generated an additional AC voltage based damping component to suppress the system instability due to the weak AC grid conditions. Firstly, a small-signal model of MMC system including SFVDC was developed, and validated by the electromagnetic transient（EMT） simulation in PSCAD/EMTDC. Then, by the eigen-analysis, the impact of damping coefficient on the system small-signal stability and the feasible region of the damping coefficient under different short circuit ratio（SCR） values were investigated. Finally, the dynamic performances were investigated when frequency varies. The results show that the proposed SFVDC approach can effectively improve the system stability margin, when the MMC system is connected to a weak AC grid.