Control and experiment of a 380-V, 15-kW motor drive using modular multilevel cascade converter based on triple-star bridge cells (MMCC-TSBC)

This paper focuses on an application of the modular multilevel cascade converter based on triple-star bridge-cells (MMCC-TSBC) to adjustable-speed motor drives. The TSBC is a direct ac-to-ac power converter capable of bidirectional power flow with three-phase sinusoidal input and output currents. Therefore, it is suitable to medium-voltage high-power motor drives requiring regenerative braking. However, the TSBC suffers from such a serious problem that capacitor-voltage fluctuation becomes larger as the motor (output) frequency is closer to the supply (input) frequency. Recent research has solved this problem by using a new control method. However, no experimental results applied this control method have been presented. The aim of this paper is to show experimental verification applying the new control method when the output frequency is close to the input frequency. A specially-designed downscaled system rated at 400 V and 15 kW is used to confirm the validity and effectiveness of the new control method.