基于CDSM-MMC的光伏直流接入系统故障分析

DC-fault analysis on CDSM-MMC based PV integration system

作为模块化多电平换流器(Modular Multilevel Converter, MMC)的一种,钳位双子模块(Clamp DoubleSub-module, CDSM)型MMC 具有直流故障自清除能力。但基于CDSM-MMC 的光伏直流接入系统,在直流故障特性等方面与其他类型MMC 构成的直流系统存在较大差异。为此,首先分析了联接变压器不同接地方式下的电容放电回路,阐述了直流故障对交流侧的影响。其次,在CDSM 故障闭锁情况下,划分了MMC 换流器端单极接地和极间短路时的故障阶段,建立各阶段的等值模型并求解。阐述了DC/DC 换流器及光伏电源对极间短路故障回路的影响,并对DC/DC 换流器侧的暂态过程进行了分析。最后,在PSCAD/EMTDC 中建立基于CDSM-MMC的光伏直流接入系统模型,验证了分析结果的正确性。

As one type of Modular Multilevel Converters (MMC), the Clamp Double Sub Module (CDSM) based MMC has the self-clearing capability of DC-side faults. However, PV integration system based on CDSM-MMC has significant differences from the DC system based on other MMC converters in terms of fault characteristics and so on. For the above reasons, capacitor discharge circuits under different grounding modes of the converter transformer are analyzed, and the impact of DC faults on the AC side is illustrated firstly. Secondly, when CDSM is blocked, the stages of the unipolar grounded fault and the bipolar short-circuit on the MMC converter side are divided, and equivalent models of each stage are built and solved. The influence of DC/DC converters and PV plants on the fault loop of bipolar faults is expounded, and the transient process on the DC/DC converter side is analyzed. Finally, the CDSM-MMC-based PV integration system model is established in PSCAD/EMTDC, and the simulation results verify the correctness of the analysis.