ABSTRACT
Large-power drives are defined as those drives beyond the reach of low-voltage (up to 660 V a.c. source) PWM voltage-source inverters (VSIs) with IGBTs (and high switching frequency). The IGBT-inverter power limit per unit has increased steadily in the last decade to about 2 MW (at the time of writing) by paralleling four 500 kW units. With respect to the voltage level, we have noted the introduction of 3–5 IGBT power cells (diode rectifier plus single-phase PWM inverter) in series per phase-properly insulated from each other and to ground to supply 1 MW (and more) a.c. motors at line voltages up to 4.5 kV (rms) [1].
