A Quantitative Analysis of Energy Storage Requirements for the Hybrid Cascaded Multilevel Converters

With an ever-increasing need for reducing the converter size in voltage source converter high voltage direct current (VSC-HVDC) systems, special attention is put towards converters with a low energy storage requirement, as energy storage is a predictor of the overall converter size. The modular multilevel converter (MMC) technology has the benefit of efficient AC/DC conversion; however, for many cases, it re-quires a large converter footprint, due to the excessive quantity of energy storage (i.e., capacitors) needed. Recently, hybrid cascaded multilevel converters (HCMCs) have been proposed, which are a combination of the simpler two- and three-level converters and cascaded full-bridge sub-modules (FBSMs), and are expected to have a lower converter footprint, due to fewer sub-modules (SMs) than the MMC. However, the degree to which the HCMCs have an improved footprint has yet to be verified. This paper puts forth a method for determination of the total amount of energy that the hybrid two-level converter (H2LC) and the hybrid three-level converter (H3LC) require. The results show that both the H2LC and the H3LC have an improved footprint compared to the conventional MMC.