This paper provides an experimental discussion on dynamic braking for an induction motor driven by a modular multilevel double-star chopper-cell (DSCC) inverter, intended for applications to large-capacity fans and compressors. Each chopper cell consists of a bidirectional chopper and a braking chopper connecting a single small-rated braking resistor in series with a single IGBT (Insulated-Gate Bipolar Transistor). Thus, this configuration leads to a “distributed” dynamic-braking system that provides the practical welcome byproduct of overvoltage protection to each chopper cell. This paper describes a unified control method of the DSCC inverter and all the braking choppers. An experimental induction-motor-drive system rated at 400V and 15kW is designed, constructed, and tested to verify the dynamic-braking performance. Experimental waveforms, along with simulated waveforms, confirm that the distributed dynamic-braking system is feasible and effective in a medium-voltage high-power DSCC inverter for an electric motor drive having large-capacity fans and compressors.
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