Since 2003, the speaker has been conducting comprehensive research on the family of modular multilevel cascade converters in his research group at Tokyo Institute of Technology. He has authored and coauthored a total of 41 IEEE Transactions/Journal papers concerning the multilevel converters in a broad sense over the last 16 years.

The speaker starts with classification and terminology of the family of modular multilevel cascade converters. Then, he provides an intensive discussion on the pros and cons of each family member in terms of circuit configuration, control, and application, along with speaker’s own thoughts and/or prospects hidden behind them. Next, he talks about control systems of two different downscaled prototypes designed and built in his research group, showing their experimental waveforms obtained from the two prototypes. One of the most major applications of the modular multilevel cascade converters is related to grid connections including, not only STATCOMs for reactive-power control, but also long-distance or short-distance HVDC systems for power transmission, frequency change, and/or asynchronous intertie between two power systems. The other is related to medium-voltage high-power motor drives based on modular multilevel double-star chopper-cell (DSCC) inverters and modular multilevel triple-star bridge-cell (TSBC) converters.

Finally, this talk ends with a real-time real-power emulator of a high-speed motor coupled with a mechanical load. The power circuit of the emulator consists of a three-phase modular multilevel DSCC rectifier, three inductors, and a single common-mode inductor. This emulator can reproduce the electrical and mechanical dynamics of both motor and load with high fidelity. Experimental waveforms obtained from the 400-Vdc, 10-kW, 300-Hz downscaled system confirm the validity and effectiveness of the emulator from both theoretical and practical points of view.