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

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. © 2019, Power System Protection and Control Press. All right reserved.