MMC-UPFC接地设计及其站内故障特性分析

The Grounding Design and Internal Fault Characteristic of MMC-UPFC

统一潮流控制器(unified power flow controller,UPFC)是一种能够独立、快速、精确、连续控制系统电压和潮流的第3代FACTS装置,基于模块化多电平(modular multi-level converter,MMC)的UPFC(简称MMC-UPFC),更加适合高压大容量的输电领域。根据MMC-UPFC的功能需求,参考MMC-HVDC接地方式,提出3种可行的MMC-UPFC接地方案,分别为联接变压器阀侧绕组星接接地、交流侧大电抗接地和交流侧接地接地变压器接地,并探讨3种接地方式下联接变压器的绕组形式和接地阻抗。然后结合仿真,在3种接地方式下分别对站内交流母线单相金属性接地和直流单极接地的故障特性分析,得出接地阻抗和阀内外部电气量的关系。结合故障性能和国内技术能力对3种接地方式进行比较,得出联接变压器阀侧绕组星接接地是MMC-UPFC较优的接地方案,并提出改进建议。

Unified Power Flow Controller（UPFC） is the third generation of FACTS devices, which can control power system voltage and paper flow fast, precisely and continuously,the UPFC based on modular multi-level converter（MMC） is more suitable for high-voltage large-capacity transmission fields. Based on the functional requirement for MMC-UPFC, 3grounding proposals were brought up i.e. converter-transformer valve side star connected grounding,AC side large inductance grounding and AC side zig-zag transformer grounding. Also,the winding connection form of converter transformer and the grounding impedance of 3 grounding methods were investigated. Through the simulation and analysis of the fault characteristics of internal ac bus and dc bus fault, the relationship between grounding impedance and internal electrical quantities of valve was derived. With considerations of the fault characteristics of 3 grounding methods and domestic technology ability, the conclusion that converter-transformer valve side star connected grounding is more advantageous in MMC-UPFC was derived, and the improvement was proposed.