Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1997-03-26
2001-07-17
Tamai, Karl (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C074S574300, C310S051000
Reexamination Certificate
active
06262505
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to uninterruptible power supply systems and particularly to flywheel systems. More particularly, the invention relates to a magnetic levitation flywheel system.
BACKGROUND OF THE INVENTION
The telephone industry has long used lead acid batteries for back-up power to provide uninterruptible service. The typical telephone network sends signals over optical fiber from the central office to a remote terminal. There, the signals are converted from optical into electrical waves and demultiplexed onto individual copper lines bundled together as trunks for connecting to the home.
Each remote terminal supports approximately 1000 homes. The cable companies use a similar configuration, where signals are sent from the “head end” (cable company office) to remote terminals servicing approximately 500 homes. At the terminals, the signal is converted from optical to electrical waves for transmission over coaxial cable to individual subscribers. In both cases the remote terminal uses power provided by the local utility to carry the signal from the terminal to the subscriber, since fiber optic cable cannot carry electricity. To support the terminal during a utility outage, the phone or cable companies install a back-up power supply, typically an uninterruptible power supply which uses batteries as a power source.
It is desirable to eliminate batteries from these networks because of their limited life, poor reliability, and high maintenance requirements. These unfavorable attributes translate to high operating cost. Although commonly used valve-regulated lead acid batteries are referred to as “maintenance free,” the batteries need continuous on-site monitoring and maintenance. The performance and life of batteries is temperature dependent. Heat degradation occurs above 77° F. (for every 15° F. increase above 77° F. the battery life is reduced by 50%). As a result, a battery schedule for ‘change out’ in five years only lasts two to three years. Batteries are also susceptible to “thermal runaway,” which can result in the release of explosive hydrogen gas. In addition, batteries are not environmentally friendly due to lead content and are coming under increasingly strict environmental and safety regulations.
One replacement for batteries is the flywheel energy storage system. Existing systems for supporting high speed flywheels utilize either mechanical contact bearings or expensive and complicated magnetic bearing systems. Mechanical rolling element bearings have very limited life due to the high rotational speeds necessary for an effective flywheel energy storage system. Further disadvantages of mechanical bearings are noise, vibration, and poor reliability in the vacuum environment required to reduce windage losses of the high speed flywheel. A non contacting support with all control apparatus outside the vacuum solves these problems. Existing magnetic levitation systems typically are either expensive due to multiple axes of active control, or suffer from complicated magnetic structures when combining active and passive control.
U.S. Pat. No. 4,211,452 describes an inertia wheel more particularly adapted to space applications. It includes the combination of a peripheral type of motor with permanent magnet on the rotor and ironless winding on the stator. This structure limits speed due to stress. The current of the winding is switched electronically by an amplitude modulation system, associated to a reactance coefficient varying circuit, and reversal of direction of rotation of which is achieved by permutation of the control circuits. There are also provided bearings formed by a passive radial magnetic centering device and a redundant active axial magnetic centering device slaved to an axial rate detector. This device requires a permanent magnet and four control coils just for axial control.
U.S. Pat. No. 4,620,752 describes a magnetic bearing having position stabilization of a supported body which includes damping and aligning arrangement. An application of the magnetic bearing is illustrated showing a magnetic bearing system for a flywheel. This system requires combining two control coils with two rotating permanent magnets for each bearing.
It can be appreciated that new and improved magnetic levitation flywheel systems are desired, in particular, for backup power supply systems to provide uninterruptible power supplies.
SUMMARY OF THE INVENTION
In accord with the present invention an uninterruptible power supply system is provided having a magnetic levitation flywheel module. The flywheel module comprises a flywheel rotor contained in a vacuum housing. The flywheel rotor is attached to a hub that is suspended from the housing by a frictionless axial magnetic bearing. Also, suspended by the magnetic bearing is the rotor of a permanent magnet motor/generator.
In accord with the present invention, a backup power supply comprises a controller and a flywheel module. The controller is configured to provide initial charge up of the flywheel to bring it up to standby speed, to keep the flywheel, speed within a predetermined range at standby, to provide a predetermined voltage to the system for uninterrupted power supply, and to monitor the status of the flywheel module.
The flywheel module comprises a vacuum housing. In the housing is a flywheel and a motor/generator. The flywheel rotor and the motor/generator rotor are mounted on a common shaft and an active axial magnetic bearing being located to support the shaft for frictionless rotation. The bearing provides support, or axial lift, for the shaft, the flywheel and the motor/generator. The axial magnetic bearing is attached to the housing and provides, in combination with the motor/generator rotor, a flux path and magnetic field that provides a magnetic force to lift the motor/generator rotor and the shaft on which it is mounted.
More particularly, the flywheel module comprises a vertical shaft on which the flywheel rotor is mounted along with the motor/generator rotor. Radially polarized permanent magnets are mounted around the motor rotor to provide at least four poles. A motor stator is fixedly mounted in relation to the rotor. Preferably, a passive radial magnetic bearing is located at one end of the shaft, more preferably at both ends. The passive radial bearing or bearings produce axial lift as well as radial centering. The axial lift offloads the active axial bearing and preferably lifts about 70% or more of the weight of the rotors. Typically, the passive bearings lift no more than 90% of the rotor weight. In one embodiment, the passive bearings lift 80% of the rotor weight.
In another embodiment, a damping device is positioned at one or, preferably, both ends of the shaft. One damping device comprises a plate member having a center bore and a sleeve positioned in the center bore and fitting around the shaft. The plate member has a chamber for containing a damping fluid. The chamber communicates with the center bore by means of a bore hole for fluid passage therebetween. The chamber also contains a spring and a plug, the plug being located between the spring and the fluid to transfer a force from the spring to the fluid or the fluid to the spring. As an alternative, an elastomeric ring can be used as a damping device.
The permanent magnetic motor/generator draws power from an electrical bus to spin-up the flywheel rotor to its steady state speed, transforming electrical energy into kinetic energy. The flywheel remains at its steady state rotational speed, drawing a nominal load from the bus. When power is required by the power supply system, the motor/generator transitions from a motor to a generator drawing energy from the flywheel for delivery to the bus.
The flywheel energy storage system (FESS) of the present invention can provide a “plug for plug” replacement for batteries in telecommunications remote powering applications such as vaults, huts and cabinets.
REFERENCES:
patent: 3323763 (1967-06-01), Butts
patent: 3860300 (1975-01-01), Lyman
patent: 3874778 (1975-04-01), Kato et al.
paten
Amaral Michael E.
Bushko Dariusz A.
Hockney Richard L.
Lansberry Geoffrey B.
Nichols Stephen B.
Dike, Bronstein, Roberts & Cushman, Intellectual Property Practi
Meuner George W.
SatCon Technology Corporation
Tamai Karl
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