Comparative Evaluation of Partially-Rated Energy Storage Integration Topologies for High Voltage Modular Multilevel Converters

This paper compares three partially-rated MMC topologies (Partially Rated Storage - PRS, Stack Parallel Branch - SPB, Inductor Parallel Branch - IPB) which integrate energy storage solutions for HVDC-scale Modular Multilevel Converters to provide with extra degrees of flexibility in the grid. The paper compares (i) the ES power that can be contributed from each topology under a given converter design and (ii) the trade-offs in terms of losses, and control adaptation required on top of a standard half-bridge MMC design in order to provide ES power. The results indicate that MMC stacks with full-bridge submodules have consistently higher ES power capability than their half-bridge counterparts - this comes at the expense of higher losses and extra devices, which for certain applications could be avoided.