Circuits and methods for preheating a rotor of a motor-generator device

A motor-generator device having circuitry that enables use of magnetic induction to preheat a rotor, the device comprising:

• electronic circuitry that generates high frequency currents;
• a plurality of armature windings that emit flux when the high frequency currents pass through the armature windings;
• and
• a rotor that conducts current induced by the flux passing through the rotor, wherein the induced current raises the temperature of the rotor.

An uninterruptible power supply system, comprising:

• a flywheel energy conversion device having a rotor;
• temperature sensing circuitry that provides a substantially accurate temperature reading of the rotor;
• and
• circuitry that provides a quantity of high frequency current to the flywheel energy conversion device to heat the rotor via magnetic induction, the quantity of current being based, at least in part, on the sensed temperature.