Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2001-10-15
2004-09-21
Le, Dang (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S209000, C310S090500
Reexamination Certificate
active
06794776
ABSTRACT:
This invention pertains to flywheel energy storage systems and more particularly to an improved inductor alternator flywheel system that eliminates power disruptions, has increased efficiency, and is more compact than previous devices. The higher efficiency of the invention allows its proficient operation with an activated field power, thus eliminating short-term interruptions of power occurring with prior systems and also potentially for allowing higher speed and higher power operation.
BACKGROUND OF THE INVENTION
Flywheel energy storage systems are being employed for supplying power to a protected load during interruptions of power from the grid. Flywheel systems use a large inertia flywheel that is supported by a bearing system and is coupled to a motor/generator. The motor/generator converts between electrical and mechanical energy by accelerating the flywheel for storing energy and decelerating the flywheel for retrieving energy. The flywheel is typically housed in a low-pressure container to limit losses from aerodynamic drag. Such systems are very advantageous for supplying back-up power to communications networks during power outages, and can also be used as ride-through devices that supply power during the start-up period that an auxiliary power source, such as a generator, needs before it can come on-line. Flywheels offer very high power capability and increased reliability over conventional electrochemical batteries, and also have longer lifespans.
To date, various types of flywheel systems have been proposed, each having different goals and attributes for their different applications. One type of flywheel system that is currently being utilized employs an inductor alternator for the motor/generator. In general, alternators use field coils that create a magnetic field which can be varied by controlling power to the field coil, and thereby control the output voltage that is generated from rotation of an armature in the magnetic field. This control can be used to maintain a relatively constant desired output voltage for a flywheel system as the speed of the flywheel slows. In contrast, conventional permanent magnet generators suffer from an output voltage that decreases linearly with speed, necessitating the use of output power conversion electronics to maintain the desired constant output voltage. For very high power systems, the cost of power electronics increases substantially, thus making an alternator flywheel system desirable.
Inductor alternators are a type of alternator particularly well suited for flywheel and other high speed applications since they have both the field and armature coils stationary. This eliminates the need to reinforce coils for high-speed rotation and also the need for electrical contact with the rotating flywheel that would require brushes that wear. Inductor alternators generate power by inducing a voltage in the armature windings from periodic changes in the magnetic flux that links the armature coils. Current in the field windings sets up the flux, and changes in the flux through the armature windings are the result of changes in the reluctance of the magnetic circuit. The rotor of the inductor alternator causes these changes by rotation of teeth or poles in an air gap in the magnetic circuit, thereby increasing and decreasing the air gap as the teeth or poles pass through it. The rotor of an inductor alternator can thus be made very simply as a gear and as such is well suited for high-speed rotation When the rotor of an inductor alternator is combined into a flywheel, the resulting device can be well suited for both storing energy and for delivering a high power constant output voltage.
One such inductor alternator flywheel system of the prior art is shown in FIG.
1
. The flywheel system
30
is comprised of a solid steel flywheel rotor
31
that rotates inside a shell
40
. The flywheel
31
has integral shafts
36
that journal the rotor inside upper and lower mechanical bearings
37
and
38
. The flywheel rotor
31
stores the kinetic energy and also serves as an inductor alternator rotor by having an outer surface defined by poles
32
, each having a radius
34
, separated by recesses
33
with radii
35
. A stationary field coil
39
generates flux, which flows axially into the flywheel
31
, then radially outward through the poles
32
and through armature coils
43
. A laminated ring
42
diffuses changes in the flux created from rotation of the flywheel poles
32
. The outer shell
40
that contains the vacuum also serves as a path for the flux to connect back to the field coil
39
and complete the magnetic circuit.
Although this type of inductor alternator flywheel system is relatively simple and is capable of supplying high levels of power, this system has several significant drawbacks. The system has power losses that generate heat during standby operation while rotating at full speed with no loss of primary power. To alleviate these losses, the power to the field coil is kept reduced when in standby mode. This reduces the flux through the rotor and its poles and the armature coils. In standby operation and also when the flywheel is accelerating, the armature coils are energized by synchronized multiphase power (typically 3 phase), to make the inductor alternator function as a motor. Energizing of a set of coils causes the rotor to rotate such that its poles or teeth tend to line up with the energized coils and when they do, the sequentially next coils are energized to propel it around. In the process, the energizing of armature coils and the rotation of rotor poles into a changing magnetic field, the magnetic flux through the rotor poles continuously changes. Changes in flux through any conductor, such as the steel rotor, cause generation of eddy currents. The large teeth allow a very big area for generation of large eddy currents. The greater the currents, the greater the loss and heat created. Losses also occur from the changing flux in the rotor due to magnetic hysteresis. Losses for the system shown in
FIG. 1
during standby operation are approximately 2 kilowatts. If the field coil is fully energized and the system is discharging, losses can expectedly be much higher. Removal of large amounts of continuous heat requires fans and periodic maintenance for cleaning air filters. More importantly, current systems operate at low tip speeds, stress levels and energy storage capability. The radial and hoop direction stresses for a 25 inch diameter flywheel rotating at 7000 rpm are shown in
FIGS. 2A and 2B
. As can be seen, the stress levels at this operating speed are low and the energy storage per the size of flywheel is low. If such flywheel inductor alternators were rotated to higher speeds to increase the energy storage density, the eddy current losses would increase with the square of the speed.
In addition to these high losses and low storage issues, another problem with the system shown in
FIG. 1
operating in stand-by mode with reduced power to the field coil is that there is a time lag before it can provide full power in the event of a power interruption. A monitoring system is used to monitor the primary power. When it senses an interruption of primary power, it sends a drive signal to the field coil in the flywheel storage unit that causes the field coil current to ramp up such that required output power is provided. Some amount of time is required between sensing the loss of power and increasing the field coil power to raise the output of the system to full power. For some critical applications such as in telecommunications, computers and semiconductor manufacturing, loss of power for even fractions of a second may be costly.
One well-known method for reducing losses in motor/generators and other magnetic circuit devices is to fabricate the magnetic path with laminated construction. The laminated construction builds the structure by stacking multiple layers of the magnetic circuit material together, each layer being electrically insulated from adjacent layers through use of insulative coatings. This constru
Le Dang
Neary J. Michael
LandOfFree
Inductor alternator flywheel system does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Inductor alternator flywheel system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Inductor alternator flywheel system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3204959