Design and Analysis of Modular Multilevel Reconfigurable Battery Converters for Variable Bus Voltage Powertrains

Larger battery packs, an efficient battery management system, highly efficient electromechanical conversion, and fast battery charging are the key factors for extending the drive range of electric vehicles and the expansion of electromobility. We present a novel highly stable modular multilevel powertrain design with a variable dc-bus voltage, active inner battery energy flow control, and reduced filter size. The underlying powertrain design replaces conventional hard-wired batteries by a modular multilevel architecture, thus modularizing the battery pack and increasing the energy efficiency, reducing the output filter size, and providing full control over the output voltage and energy flow of the battery cells. We analyse the large-signal stability of the proposed system and compare it to dc/dc-dc/ac conventional multiconverter powertrains, demonstrating better stability and lower filter requirements. Further, we experimentally evaluate the proposed system structure. In the experimental setup, we achieve stable converter operation with the output filter capacitor reduced by a factor of 24 and the filter inductor reduced by a factor of 17 compared to dc-dc-dc-ac reference system, thereby leading to a significant reduction of system cost, size, and weight.