Three plus three phase flywheel electric power supply

1. A flywheel electric power supply comprising:

a motor-generator including a rotor and a stator;

a flywheel mass coupled to and constrained to rotate in synchrony with the rotor;

the flywheel mass bi-directionally exchanging mechanical power with the motor-generator;

a plurality of windings on the stator forming six electrical phases A, B, C, D, E and F;

one or more stator windings bi-directionally exchanging electric power with one or more AC to DC converters; and,

one of the AC to DC converters coupled to an electrical network for providing backup power to the electrical network.

2. The flywheel power supply of claim 1 further comprising:

a first three phase motor-generator including the rotor and windings of three of the electrical phases A-C of the stator;

a second three phase motor-generator including the rotor and windings of three of the electrical phases D-F of the stator;

the first three phase motor-generator bi-directionally exchanging electric power with a first AC to DC converter; and,

the second three phase motor-generator bi-directionally exchanging electric power with a second AC to DC converter.

3. The flywheel power supply of claim 2 wherein the flywheel rotates about a substantially vertical axis.

4. The flywheel power supply of claim 3 further comprising a stator support structure from which the stator is hung.

5. The flywheel power supply of claim 4 further comprising a first chamber partially enveloped by the stator support structure and enveloping the rotor.

6. The flywheel power supply of claim 5 further comprising a second chamber enveloping the flywheel mass and substantially enveloping the first chamber.

7. The flywheel power supply of claim 6 further comprising a vacuum pump operable to transfer gas from the second chamber to the first chamber.

8. The flywheel power supply of claim 1 further comprising:

a first three phase motor-generator including the rotor and windings of three of the electrical phases A-C of the stator;

a second three phase motor-generator including the rotor and windings of three of the electrical phases D-F of the stator;

a first power electronics package exchanging power with electrical phases A-C of the stator;

a second power electronics package exchanging power with electrical phases D-F of the stator; and,

at least one of the power electronics packages bi-directionally exchanging power with an electrical network and providing back-up power to one or more loads on the network.

9. The flywheel power supply of claim 8 further comprising:

independent first and second power electronics controllers controlling first and second AC to DC converters;

DC connections of each of the first and second AC to DC converters interconnected by a DC bus;

first and second independent voltage indicating devices providing first and second indications of DC bus voltage V 1 , V 2 ; and,

first and second power electronics controllers utilizing an average of the indicated bus voltages ((V 1 +V 2 )/2) for controlling respective AC to DC converters.