Multi-level converter
A multi-level converter (MLC) is a method of generating high-voltage wave-forms from lower-voltage components. MLC origins go back over a hundred years, when in the 1880s, the advantages of DC long-distance transmission became evident.<ref>Arrillaga, Jos (1998). "Chapter 1". High Voltage Direct Current Transmission (Second ed.). Institution of Electrical Engineers. p. 1–9. ISBN 0852969414.</ref>
Modular multi-level converters (MMC) were investigated by Tricoli et al in 2017. Although their viability for electric vehicles (EV) was established, suitable low-cost semiconductors to make this topology competitive are not currently available (as of 2019).<ref>Tricoli, Pietro (Mar 2017). "Efficiency assessment of modular multilevel converters for battery electric vehicles" (PDF). IEEE Transactions on Power Electronics. 32 (3): 2041–2051. Bibcode:2017ITPE...32.2041Q. doi:10.1109/TPEL.2016.2557579. S2CID 8412590.</ref>
In 1999, Tolbert described the use of MLC for battery operated electric motors.<ref>Tolbert, Leon M. (Jan–Feb 1999). "Multilevel Converters for Large Electric Drives". IEEE Transactions on Industry Applications. 35 (1): 36–44. CiteSeerX 10.1.1.468.9074. doi:10.1109/28.740843.</ref>
Habib's 2018 review paper<ref>Habib, Salman (Jan 2018). "Assessment of electric vehicles concerning impacts, charging infrastructure with unidirectional and bidirectional chargers, and power flow comparisons". Int J Energy Res. 42 (11): 3416–3441. doi:10.1002/er.4033. S2CID 104109087.</ref> reviews multi-level inverters (a synonym for MLC) stating the advantages of bi-directional energy flows to power the motor or charge the battery system.
High voltage DC converters
HVDC converters typically use series connected switched capacitors blocks. The blocks are switched in or out of the circuit to form the desired waveform, typically three phase AC.
Low voltage DC converters
Hydrogen generation via electrolysis requires DC currents over several thousand amperes, but DC voltages in the range of only 100...400 VDC. A high voltage modular multi-level converter (MMC) can be adapted by connecting a galvanically isolated LLC Resonant converter to each module capacitor.<ref>Unruh, Roland; Schafmeister, Frank; Böcker, Joachim (November 30, 2020). "11kW, 70kHz LLC Converter Design with Adaptive Input Voltage for 98% Efficiency in an MMC". 2020 IEEE 21st Workshop on Control and Modeling for Power Electronics (COMPEL). pp. 1–8. doi:10.1109/COMPEL49091.2020.9265771. ISBN 978-1-7281-7160-9. S2CID 227278364 – via IEEE Xplore.</ref> Several half-bridge and full-bridge based MMC topologies are evaluated in.<ref>Unruh, Roland (October 2020). "Evaluation of MMCs for High-Power Low-Voltage DC-Applications in Combination with the Module LLC-Design". 22nd European Conference on Power Electronics and Applications (EPE'20 ECCE Europe). doi:10.23919/EPE20ECCEEurope43536.2020.9215687. ISBN 978-9-0758-1536-8. S2CID 222223518.</ref> Such a converter can also be used to provide a centralized 400V DC power supply for data centers.
M2LeC
M2LeC (pronounced Emlek), is a form of multi-level converter that combines the functions of generating electric motor wave-forms, with battery charging and management in a single set of power electronics hardware, where the various functions are performed through software alone.
