Experimental Verification of an Electrical Drive Fed by a Modular Multilevel TSBC Converter When the Motor Frequency Gets Closer or Equal to the Supply Frequency

This paper provides an experimental discussion on an adjustable-speed electrical drive fed by a modular multilevel triple-star bridge-cell (TSBC) converter. The TSBC converter is suitable for medium-voltage high-power motor drives with regenerative braking. However, it suffers from capacitor-voltage fluctuation that becomes more serious as the motor frequency gets closer or equal to the supply frequency. This paper presents a practical solution of it with an acceptable increase in all the nine cluster currents. The solution is characterized by a motor-magnetizing-current controller that makes a significant contribution to theoretically eliminating the low-frequency component contained in each capacitor voltage. Experimental waveforms, which are obtained from a three-phase downscaled model rated at 400 V and 15 kW, verify exhibit satisfactory start-up performance from a standstill to the rated motor frequency that is equal to the supply frequency.