Experimental verification of TSBC-based electrical drives when the motor frequency is passing through, or equal to, the supply frequency

This paper provides an experimental discussion on adjustable-speed electrical drives using a modular multilevel cascade converter based on triple-star bridge cells (MMCC-TSBC) when the motor frequency is passing through, or equal to, the supply frequency. The TSBC converter is one of the most suitable candidates for medium-voltage, high-power motor drives with regenerative braking. However, its capacitor-voltage fluctuation becomes larger as the motor frequency gets closer to the supply frequency. This paper presents a practical solution to overcome it with acceptable circulating currents. This makes it possible to modify a line-started motor loaded at the rated torque into an adjustable-speed drive. Experimental waveforms exhibit satisfactory start-up performance from a standstill to the rated motor frequency, passing through the supply frequency.