Abstract: A motor drive system for a mining shovel includes three a.c. motors which are driven by associated inverter circuits that receive power from a common d.c. bus. The d.c. bus connects to the a.c. power lines through a rectifier circuit and large variations in power occur during various portions of the digging cycle. To limit the peak power demanded during a digging cycle a peak power limiter system comprised of a fourth inverter driven a.c. motor is attached to the d.c. bus. This a.c. motor drives a flywheel which is operated to store energy during periods of low power demand and which is operated to regenerate stored energy to the d.c. bus when power demanded from the a.c. power lines exceeds a preset amount.