王鋆鑫, 汪晋安, 许建中. 不平衡网压下混合模块化多电平换流器子模块电容过压抑制策略[J]. 现代电力, 2023, 40(5): 853-862. DOI: 10.19725/j.cnki.1007-2322.2022.0071
引用本文: 王鋆鑫, 汪晋安, 许建中. 不平衡网压下混合模块化多电平换流器子模块电容过压抑制策略[J]. 现代电力, 2023, 40(5): 853-862. DOI: 10.19725/j.cnki.1007-2322.2022.0071
WANG Yunxin, WANG Jinan, XU Jianzhong. Overvoltage Suppression Strategy of Hybrid MMC Sub-modules Capacitor Under Unbalanced Grid Voltages[J]. Modern Electric Power, 2023, 40(5): 853-862. DOI: 10.19725/j.cnki.1007-2322.2022.0071
Citation: WANG Yunxin, WANG Jinan, XU Jianzhong. Overvoltage Suppression Strategy of Hybrid MMC Sub-modules Capacitor Under Unbalanced Grid Voltages[J]. Modern Electric Power, 2023, 40(5): 853-862. DOI: 10.19725/j.cnki.1007-2322.2022.0071

不平衡网压下混合模块化多电平换流器子模块电容过压抑制策略

Overvoltage Suppression Strategy of Hybrid MMC Sub-modules Capacitor Under Unbalanced Grid Voltages

  • 摘要: 通过注入一定量的二次谐波电流,能够抑制模块化多电平换流器(modular multilevel converter, MMC)的子模块电容电压纹波,降低对电容值的需求,从而减少MMC换流阀的体积和成本。此外,当电网电压不平衡时,子模块电容电压纹波将会变大,如果不采取合适的策略,有可能会造成子模块的过电压。针对上述问题,提出一种适用于混合型MMC在不平衡网压工况下的二次谐波电流注入策略。首先建立不平衡网压工况下的MMC数学模型;接着分析子模块电容电压的纹波特性,揭示子模块电容电压和桥臂功率波动的关系;基于桥臂瞬时功率模型提出谐波注入参数的优化策略和计算过程;最后在PSCAD/EMTDC搭建混合型MMC仿真模型来验证所提策略的有效性。仿真结果表明,所提策略能够有效地抑制几种典型的不平衡网压下的电容电压纹波。

     

    Abstract: By means of injecting a certain amount of second harmonic current, the submodule capacitor voltage ripples of modular multilevel converter (abbr. MMC) can be suppressed to reduce the demand on the submodule capacitance, thus, the volume and cost of MMC converter valve can be reduced. Besides, under the unbalanced grid voltage the voltage ripple of the submodule capacitance increases, if adequate strategy is not adopted the overvoltage of submodule might be caused. In allusion to above-mentioned problems, a second harmonic current injection strategy suitable to hybrid MMC under imbalance grid voltage was proposed. Firstly, a mathematical model for MMC under the unbalanced grid voltage was established. Secondly, the ripple characteristic of the voltage of the submodule capacitance was analyzed to reveal the relation between the voltage of the submodule capacitance and the power fluctuation of bridge arms. Thirdly, based on the instantaneous power model of bridge arms the optimizing strategy and computing process of harmonic injection parameters was put forward. Finally, on the platform of PSCAD/EMTDC, a simulation model of hybrid MMC was constructed to verify the effectiveness of the proposed strategy. Simulation results show that the capacitor voltage ripple under several typical unbalanced grid voltages can be effectively suppressed by the proposed strategy.

     

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