DC Fault ride-through capability of Modular Multilevel Converters
Fig.1 (a) shows the conventional MMC with half bridge modules during the DC fault. The DC fault occurrence analysis is carried out in the MMC with half bridge power cells and the uncontrollable current path during the DC terminal short circuit. Fig.1 (b) depicts the MMC as it contains full-bridge power cells during the DC short circuit. To have a sequential and coherent analysis, the operation of the MMC with Full-bridge modules, should be demonstrated during the short circuit of the DC-link and then, the DC-fault blocking capability of the MMC with Full-bridge power cells should be presented.
The recently published Alternate Arm Converter (AAC), which is from the family of the hybrid multilevel voltage source converter, is shown during the DC fault in Fig1. (c). AAC has nearly the same number of semiconductor devices in its topology, and it requires less arm inductor and power cell capacitor size. The main benefit of the AAC is the excellent performance and ride through capability in a local terminal to terminal short circuit of the DC-link and three different possible modes of STATCOM operation during the DC fault. In this paper, the DC-fault blocking of the AAC will mainly be considered for medium voltage DC applications and the DC fault current during the fault will be analyzed.