Integration of a Clamp Double Submodule Based on Integrated Chips for MMC Reliability Improvement

Among different modular multilevel converters (MMCs) submodules (SMs), the clamp double submodule (CDSM) has the capability of dc-fault current clearing with a relatively small number of switching devices. Furthermore, the control scheme of CDSM-MMC is compatible to the HBSM-MMC in normal operation. Hence, CDSM is a cost-effective and promising solution for the MMCs with dc-fault handling capability. The dc-fault handling capability of CDSM is realized by adding an insulated gate bipolar transistor (IGBT) with its anti-paralleled diode and two independent diodes for every two HBSMs. The IGBT and its anti-paralleled diode connect the two HBSMs. However, since the connecting devices with greater current loading would be subject to extremely higher temperature and larger temperature excursion, the lifetime of the CDSM is severely limited. In this paper, a CDSM based on integrated chips is integrated. No additional cooling components and software-based techniques are introduced. The finite element method (FEM) simulation results show that the thermal stress of the connecting device can be reduced significantly by using integrated chips. And the lifetime of the connecting devices extends greatly. Finally, the advantages of the CDSM based on integrated chips is verified by experiments.