Comparison of Modular Multilevel Converter Based High Voltage-Step-Down Ratio DC/DC Converters for Energy Storage System Applications

This paper presents a review and comparison of high voltage-step-down ratio dc/dc converters based on the modular multilevel converter (MMC) or quasi-MMC, specifically designed for medium-voltage direct current (MVDC) grid-tied energy storage systems (ESS). The paper discusses various topology configurations and their operational features. The surveyed topologies are compared in terms of switching device cost, switching device power losses, passive component volumes, voltage-step-down ratios, and frequency multiplication ratios. Case studies are performed on selected topologies using specifications of 7-kV input voltage, 250-V-to-450-V output voltage, and 250-kW transferred power. This review highlights the potentials of MMC-based dc/dc converters and provides an analysis of the pros and cons of different topologies.