The modular multilevel cascade converter (MMCC) family consists of several members with different given names. These members with the family name “MMCC” have similar circuit configurations based on either single-phase full-bridge (H-bridge) ac/dc converters called simply as “bridge cells” or non-isolated bidirectional dc/dc choppers called just as “chopper cells.” However, these family members have different characters from a practical point of view. Among them, this talk pays attention to two specific family members with given names “double-star chopper cells (DSCC)” for grid connections and motor drives, and “triple-star bridge cells (TSBC)” for motor drives. Although the full names are “MMCC-DSCC” and “MMCC- TSBC,” they are called and treated just as a “DSCC” and a “TSBC” like countable nouns for the sake of simplicity. The DSCC is the same in circuit configuration as a specific modular multilevel converter called as an “MMC.” When a power electronics engineer uses the term “modular multilevel converter” in his/her technical paper/article or presentation, the other engineers, especially graduate students and young engineers, cannot identify the circuit configuration or may have a misunderstanding about it in the worst case. However, no misunderstanding would happen as long as the term “modular multilevel converters” implied general multilevel converters characterized by modular structure. This talk focuses on circuit configurations, controls and applications of both DSCC and TSBC for high-voltage grid connections and medium-voltage motor drives, showing experimental waveforms obtained from three different downscaled prototypes that have been designed, constructed, and tested in the speaker’s laboratory. Generally, a DSCC-based motor drive is different in application from a TSBC-based motor drive: The former is suitable for a medium-voltage high-power application, in which the load torque is proportional to a square of rotating speed, whereas the latter is suitable f medium voltage high-power application, in which the load requires the rated torque in a range from zero speed to the rated speed.
Hirofumi Akagi received the B. S. degree from the Nagoya Institute of Technology, Nagoya, Japan, in 1974, and the M.S. and Ph. D. degrees from the Tokyo Institute of Technology, Tokyo, Japan, in 1976 and 1979, respectively, all in electrical engineering. He Is currently Professor and Chair of the department of electrical and electronic engineering at the Tokyo Institute of Technology. His research interests include power conversion systems, motor drives, active and passive EMI filters, high-frequency resonant inverters for induction heating and corona discharge treatment processes, and utility applications of power electronics such as active filters, self-commutated BTB (back-to-back) systems, and FACTS (flexible ac transmission systems) devices. He has published more than 80 IEEE Transactions papers and two invited papers published in Proceedings of the IEEE.
Dr. Akagi is a former President of the IEEE Power Electronics Society. He was elected as an IEEE Fellow in 1996 and as a Distinguished Lecturer of the IEEE Power Electronics and Industry Applications Societies for 1998-1999. He has received four IEEE Transactions Prize Paper Awards, nine IAS commitee prize paper awards, the IEEE William E. Newell Power Electronics Award, the IEEE Industry Applications Society Outstanding Achievement Award and the IEEE Richard H. Kaufmann Technical Field Award.