The ATRUs produce both plus and minus 270 V DC outputs. The Motor Controllers modulate the duration for which the dc power from each output is alternately applied to the motors - with longer pulses at the start reduced to shorter and shorter pulse width as the motor accelerates.
By the way, the additional weight of the electrical components is counter-acted by there being no need for a separate starter motor, start control valve, pneumatic supply - or even a (notoriously unreliable) pneumatic system at all. Hallelujah!
Now for the hydraulics, Heh! Heh!
