A low-speed, high-torque motor drive using the modular multilevel cascade converter based on triple-star bridge cells (MMCC-TSBC)

This paper provides an experimental discussion on the modular multilevel cascade converter based on triple-star bridge cells (MMCC-TSBC) for a low-speed high-torque motor drive. The TSBC is a direct ac-to-ac power converter capable of achieving bidirectional power flow as well as drawing and feeding three-phase sinusoidal input (supply-side) and output (motor-side) currents with any power factor at both sides. This paper pays attention to active dc-capacitor-voltage control and ac inductor design, devoting itself to the low-speed, high-torque motor drive. A specially-designed downscaled system combining a 320-V, 38Hz, 6-pole, 15-kW induction motor with a 400-V, 15-kW TSBC is constructed and tested to confirm the validity of the proposed control and design. Experimental waveforms obtained from the downscaled system verify stable operation with the rated torque across a range from a standstill to the rated speed, including satisfactory start-up performance.