摘要
为解决模块化多电平换流器在充电阶段过渡时易出现的电流过冲问题,以及因不当投切引起的模块过充问题,深入分析了换流器内子模块电容的预充电过程,并根据子模块电容的充电特点提出了一种适用于可控充电阶段的有源交流侧均衡控制充电策略。通过母线电压定斜率控制固定上、下桥臂的子模块投切数目,避免数目突变。同时,在充电过程中为使各臂子模块电容电压可准确跟踪其参考值,考虑了环流压降对桥臂子模块充电的影响,引入环流稳压控制环节对臂间子模块投切比例进行动态微调,从而保证子模块充电效果,提高相间充电一致性。最后,在PSCAD/EMTDC中搭建了双端有源换流器预充电仿真模型,验证了上述充电策略的有效性,该策略控制下电容电压及直流母线电压平稳抬升,系统实现由不可控充电阶段到可控充电阶段的安全过渡。
To solve the problem of current overshoot in a modular multilevel converter(MMC) during the transition in its charging phase and the problem of module overcharge caused by incorrect switching, the pre-charging process of a sub-module capacitor in the converter is analyzed. In addition, according to the charging characteristics of the sub-module capacitor, an active AC-side equalization control charging strategy which is suitable for the controllable charging phase is proposed. The switching number of sub-modules on the upper and lower bridge arms is controlled by the bus voltage constant slope to avoid a sudden change in this number. Meanwhile, to ensure that the capacitor voltage of each bridge arm sub-module can accurately track its reference value, the influence of voltage drop resulting from the circulating current on the charging of bridge arm sub-module is taken into account, and the switching ratio of bridge arm submodules is dynamically adjusted through the introduction of a circulating current stabilizing control link, thus guaranteeing the charging effect of sub-modules and improving the charging consistency among different phases. Finally, a precharging simulation model of a dual-terminal active converter is built in PSCAD/EMTDC to verify the effectiveness of the proposed charging strategy, under which the capacitor voltage and DC bus voltage are raised steadily and the safe transition from an uncontrollable to a controllable charging phase is realized in the system.
作者
王立权
宋吉江
鲁尧
王雪姣
WANG Liquan;SONG Jijiang;LU Yao;WANG Xuejiao(School of Electrical and Electronic Engineering,Shandong University of Technology,Zibo 255049,China)
出处
《电源学报》
CSCD
北大核心
2022年第5期135-141,共7页
Journal of Power Supply
关键词
模块化多电平换流器(MMC)
可控充电
均衡控制
电流过冲
模块过充
环流
modular multilevel converter(MMC)
controllable charging
equalization control
current overshoot
module overcharge
circulating current
