Multiple medium-voltage motor drives using modular multilevel cascade converters with medium-frequency transformers

This paper provides a multiple motor drive using modular multilevel cascade converters (MMCCs) with galvanic isolation achieved by medium-frequency transformers. The motor drive is suitable for large-capacity pump and conveyor applications where multiple motors are required. A mitigating control method designed for the motor drive can reduce inherent capacitor-voltage fluctuation in each floating dc capacitor. As a result, the capacitance values can be dramatically reduced, compared to the already-existing MMCCs. Simulated waveforms verify the effectiveness of the multiple motor drives and its mitigating control method. These results are obtained from two 6-kV 2.5-MW loads fed by a converter system consisting of a single supply-side MMCC, two load-side MMCCs, and two 450-Hz single-phase transformers.