Magnetically coupled flywheel

1. A flywheel energy storage system for storing electrical energy, the system comprising:

a plurality of flywheels, each of the flywheels including a rotatable mass and a shaft, the flywheel being enclosed within an evacuable enclosure, the shaft supported by bearings on opposite sides of the rotatable mass, a rotor being fixed to the shaft in a cantilevered manner within the enclosure; and

at least one electric motor/generator unit having a stator that is locatable outside of the enclosure of each flywheel of said plurality of flywheels and that is configured to be magnetically coupled to the rotor of one flywheel of said plurality of flywheels, the motor/generator unit being moveable to separately magnetically couple to the rotor of each flywheel of said plurality of flywheels.

2. The system of claim 1 , comprising an engagement/disengagement mechanism to adjust a distance between the rotor and the stator.

3. The system of claim 1 , wherein the flywheel comprises lead enveloped in a shell that comprises carbon fiber.

4. The system of claim 1 , wherein the flywheel comprises a plurality of glass fibers, each fiber being at least partially wrapped around a column of a plurality of columns that are arranged in a circular pattern that is centered on an axis of rotation of the flywheel, such that each fiber extends substantially radially outward from the axis when the flywheel rotates.

5. The system of claim 1 , wherein the flywheel includes a structure with an eccentric mass distribution that is rotatable to adjust a balance of the flywheel.

6. The system of claim 1 , wherein a section of the enclosure between the rotor and the stator comprises glass.

7. The system of claim 1 ,

wherein the bearings comprise a mechanical bearing to continuously support a shaft of the rotating load so as to hold the shaft at a substantially fixed axis of rotation and a magnetic stabilization assembly including a plurality of electromagnets arranged around the shaft,

the system further comprising a control circuitry for controlling a resultant magnetic field generated by the electromagnets such that the magnetic field acts on a ferromagnetic element of the shaft to reduce imbalance forces acting on the shaft.

8. The system of claim 7 , comprising a sensor to sense a vibration of the shaft, the control circuitry being configured to control the resultant magnetic field so as to minimize the sensed vibration.

9. The system of claim 1 , wherein said at least one motor/generator unit comprises a plurality of the motor/generator units, the system further comprising:

a direct current (DC) bus:

a plurality of controller/inverters, each controller/inverter being electrically coupled to a motor/generator unit of said plurality of the motor/generator units and to the DC bus; and

a central controller to control each controller/inverter so as to set a discharge rate for each of the flywheels when its motor/generator unit is operating in a discharge mode, and to increase a voltage level of a voltage signal generated by the motor/generator unit in the discharge mode.

10. The system of claim 1 , wherein a cap of the enclosure between the stator and the rotor comprises a magnetically susceptible material.

11. The system of claim 10 , wherein the magnetically susceptible material comprises fiberglass.

12. The system of claim 10 , wherein the magnetically susceptible material comprises a glass composite material.

13. The system of claim 1 , wherein the distance between the stator and the rotor is substantially equal to 3 mm.

14. The system of claim 1 , wherein the motor/generator unit comprises a DC motor.