Study on Modular Multi-Level DC-DC Converter with Cell Voltage Balancing and Fast Output Response Using Sub Commutation Circuits

TLDR: A circuit topology and control method of the MMC-based DC-DC converter with cell voltage balancing and fast dynamic response while the DC-AC and AC-DC converters are not used is proposed.

Abstract: DC power supplies for a battery testing are becoming significantly important for developments of electrical vehicles (EVs), mobile devices, and renewable energy generations. In the recent decade, modular multi-level converters (MMC) have been actively studied and started to use on some practical applications such as high- or medium-voltage DC-AC or AC-DC power converters. However, the widely used MMC topology has a significant issue to extend to a DC-DC converter, because it cannot achieve capacitor voltage balancing of each cell unlike the case of the DC-AC and AC-DC conversions. Therefore, most of the MMC-based DC-DC converters are realized by combining the DC-AC converter, isolation transformer or inductor, and AC-DC converter. In this study, the DC-DC operation in the MMC and its problem are analyzed and clarified. This paper proposes a circuit topology and control method of the MMC-based DC-DC converter with cell voltage balancing and fast dynamic response while the DC-AC and AC-DC converters are not used. Simulation results verify the validity of the capacitor voltage balancing control. Finally, an experimental result in a prototype converter with 6-cells using SiC-MOSFETs shows the performances of the voltage balancing control and fast dynamic response.