U.S. patent application number 15/137355 was filed with the patent office on 2016-08-18 for flywheel energy system.
The applicant listed for this patent is Temporal Power Ltd.. Invention is credited to Jeffrey Allan VELTRI.
Application Number | 20160241106 15/137355 |
Document ID | / |
Family ID | 45063902 |
Filed Date | 2016-08-18 |
United States Patent
Application |
20160241106 |
Kind Code |
A1 |
VELTRI; Jeffrey Allan |
August 18, 2016 |
Flywheel Energy System
Abstract
An energy storage system comprises a housing and a flywheel
having a drive shaft portion attached to a cylindrical
ferromagnetic rotor portion. The drive shaft portion defines a
substantially vertical axis about which the rotor portion is
mounted for rotation.
Inventors: |
VELTRI; Jeffrey Allan;
(Burlington, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Temporal Power Ltd. |
Mississauga |
|
CA |
|
|
Family ID: |
45063902 |
Appl. No.: |
15/137355 |
Filed: |
April 25, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13153216 |
Jun 3, 2011 |
9325217 |
|
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15137355 |
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61352810 |
Jun 8, 2010 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F16C 2361/55 20130101;
F16C 32/0417 20130101; F16C 19/546 20130101; Y02E 60/16 20130101;
F16C 19/543 20130101; H02J 3/30 20130101; H02K 7/09 20130101; F16C
23/08 20130101; F16C 19/163 20130101; F16C 39/063 20130101; F16C
35/077 20130101; H02K 7/025 20130101; F16F 2222/06 20130101; H02J
15/00 20130101; F16F 15/3156 20130101 |
International
Class: |
H02K 7/02 20060101
H02K007/02; H02K 7/09 20060101 H02K007/09 |
Claims
1. An energy storage system comprising: a first housing having an
end face; a flywheel having: a rotor, and a drive shaft defining a
substantially vertical axis about which the rotor is .mounted for
rotation within the first housing; a permanent magnetic bearing
assembly positioned between the end face and the rotor and having a
permanent magnet mounted on the first housing or the rotor, and the
other of the first housing or the rotor having ferromagnetic
properties, to attract the rotor towards the end face; a first
mechanical bearing assembly acting between the first housing and
the rotor to provide radial positioning of the rotor and to limit
upward axial movement of the rotor in relation to the end face, the
rotor being spaced from the end face by a clearance gap; and a
second mechanical bearing assembly spaced from the first mechanical
bearing assembly along the drive shaft and acting between the first
housing and the rotor to provide radial positioning of the rotor,
the second mechanical bearing assembly permitting relative axial
movement between the drive shaft and the first housing.
2. The energy storage system according to claim 1, wherein the
first mechanical bearing assembly also limits downward axial
movement of the rotor in relation to the end face, limiting the
size of the clearance gap.
3. The energy storage system according to claim 1, wherein the
permanent magnet is mounted on the end face.
4. The energy storage system according to claim 3, wherein the end
face of the first housing extends radially beyond the permanent
magnet to overlie the rotor.
5. The energy storage system according to claim 4, wherein the
clearance gap is maintained beyond the permanent magnet.
6. The energy storage system according to claim 4, further
comprising a non-magnetic barrier between the permanent magnet and
the end face.
7. The energy storage system according to claim 3, wherein the
permanent magnetic bearing assembly further includes: an annular
backing plate of ferromagnetic metal mounted to a top wall surface
of the first housing in stationary centered relation about the
vertical axis, the backing plate having a radius greater than or
equal to a radius of the rotor, the permanent magnet being attached
to an undersurface of the backing plate.
8. The energy storage system according to claim 1, wherein the
permanent magnet is magnetized parallel to the vertical axis.
9. The energy storage system according to claim 1, wherein the
permanent magnet includes a layer of magnetized material.
10. The energy storage system according to claim 1, wherein the
permanent magnet includes a plurality of vertically stacked layers
of magnetized material, each of the layers having its poles aligned
in a same magnetic direction as any adjacent layer of the plurality
of vertically stacked layers.
11. The energy storage system according to claim 10, wherein the
layer includes a plurality of elongate strips of magnetized
material laid parallel to one another in a side-by-side contacting
relationship.
12. The energy storage system according to claim 10, wherein the
layers are formed in a series of concentric circles of widening
radius wrapped around the vertical axis, and formed of magnetized
material comprised of are earth magnetic particles and a polymer
binder.
13. An energy storage system comprising: a flywheel housing; a
flywheel positioned within the flywheel housing, the flywheel
having: a rotor, and a drive shaft defining a substantially
vertical axis about which the rotor is mounted for rotation within
the flywheel housing; a motor/generator housing detachably attached
to the flywheel housing; a motor/generator positioned within the
motor/generator housing, the motor/generator being detachably
attached to the rotor.
14. The energy storage system according to claim 13, wherein the
motor/generator Lousing is detachably attached to a top portion of
the flywheel housing.
15. The energy storage system according to claim 13, wherein the
motor/generator comprises a coupling shaft for an axially slidable
engagement with the rotor.
16. The energy storage system according to claim 13, wherein the
motor/generator housing and motor/generator can be detached from
the flywheel housing, and wherein a second motor/generator housing
and a second motor/generator can be detachably attached to the
flywheel housing.
17. The energy storage system according to claim 16, wherein the
second motor/generator has a higher power rating than the
motor/generator.
18. An energy storage system comprising: a motor/generator housing;
a motor/generator positioned within the motor/generator housing; a
flywheel housing having a vacuum port; a flywheel positioned within
the flywheel housing, the flywheel having: a rotor, and a drive
shaft defining a substantially vertical axis about which the rotor
is mounted for rotation within the flywheel housing; and a vacuum,
pump connected to the interior volume of the flywheel housing via
the vacuum port, wherein the vacuum pump is configured to be
energized from electricity supplied by the motor/generator.
19. The energy storage system according to claim 18, wherein the
vacuum pump is configured to be energized from electricity supplied
by an electrical power grid.
20. The energy storage system according to claim 19, wherein the
vacuum pump is configured to be energized from electricity supplied
by the motor/generator when electricity supplied by the electrical
power grid is not available.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 13/153,216, filed Jun. 3, 2011, which claims
the benefit of U.S. Provisional Patent Application No. 61/352,810,
filed Jun. 8, 2010. The contents of each of these applications are
expressly incorporated herein by reference in their entireties.
FIELD OF THE INVENTION
[0002] The present invention relates to energy storage systems, and
more specifically to energy storage systems capable of storing
electrical energy as kinetic energy of a rotating flywheel, for
release of the stored kinetic energy as electrical energy when
required.
DESCRIPTION OF THE PRIOR ART
[0003] Large-scale energy storage has the potential to solve many
challenges related to modernizing electrical power distribution.
Some of these challenges include managing intermittent renewable
energy generation, electricity load shifting, black-start
capabilities, managing electricity price fluctuations, and back-up
power supply.
[0004] Currently, there are several large-scale energy storage
technologies that attempt to address the challenges facing the
energy storage industry. These technologies include advanced
batteries, electrochemical capacitors (EC), pumped hydro,
compressed air energy storage, and flywheel technologies.
[0005] With respect to the advanced batteries technologies, one
such technology--the lead acid battery, has been a popular choice
for power quality and UPS applications due to the low cost
associated with such batteries. However, the effectiveness of lead
acid batteries for large-scale applications is limited by the very
short life cycle of such batteries, and the variable discharge
rate. Li-ion batteries are often seen as an alternative or
replacement for lead acid batteries because of their much longer
life cycle. Development of the Li-ion battery has been driven to
date primarily by the automobile industry, with potential
applications for vehicular, residential and commercial use. The
effectiveness of Li-ion batteries as suitable energy-storage
technology is, however, limited by the high cost associated with
the manufacture of such batteries, and by security concerns
associated with large-scale implementations of Li-ion batteries.
Metal-Air batteries are the most compact and potentially the least
expensive battery to manufacture. However, the effectiveness of
Metal-Air batteries is limited by the very short life cycle and low
efficiencies (e.g., approximately 50%) of such batteries. One
particular battery technology that has shown promise as a solution
for large-scale implementations is the sodium-sulphur (NaS) battery
technology. NaS batteries have high energy density but require high
operating temperatures and have a relatively short life span. The
above-identified battery technologies typically have an average AC
to AC round-trip efficiency of approximately 64%. Moreover,
electrochemical battery technology, in general, have a usable life
that is degraded by the number of charge/discharge cycles.
[0006] Electrochemical capacitors (EC) are also used as an energy
storage solution. ECs are energy storage devices that have longer
life cycles and are more powerful than lead-acid batteries.
However, it is not feasible to implement ECs on large-scale
projects due to their high cost and low energy density.
[0007] A potential solution to large-scale implementations of
energy storage technology is pumped hydro. Conventional pumped
hydro uses two water reservoirs, which are separated vertically and
thus have an energy potential associated with the energy of the
water travelling from the elevation of higher potential energy to
the elevation of lower potential energy by means of gravity. During
off-peak hours, electrical power is used to pump water from the
lower reservoir to the upper reservoir. As demand for electrical
energy increases, the water flow is reversed to generate
electricity. Pumped storage is the most widespread energy storage
system in use on power networks. The main applications for pumped
hydro are energy management and frequency control. The main
drawbacks associated with pumped hydro are the unique site
requirements and the large upfront capital costs.
[0008] Another potential energy-storage solution is compressed air
energy storage (CAES). CAES uses a combination of compressed air
and natural gas. A motor pushes compressed air into an underground
cavern at off-peak times. During on-peak times, compressed air is
used in combination with gas to power a turbine power plant. A CAES
uses roughly 40% as much gas as a natural gas power plant. A CAES
has similar wide-scale use limitations as pumped hydro: the site
locations and large upfront capital costs.
[0009] Another proposal for large-scale energy storage
implementations is flywheel energy storage systems, which have
emerged as an alternative to the above-identified energy storage
technologies. Such systems are currently used in two primary
commercial applications: uninterruptible power supply (UPS) and
power frequency regulation (FR). Both UPS and FR require extremely
quick charge and discharge times that are measured in seconds and
fractions of seconds. Flywheel technologies have many advantages
over other energy storage technologies, including higher
reliability, longer service life, extremely low maintenance costs,
higher power capability, and environmental friendliness. Flywheel
energy storage systems store energy in a rotating flywheel that is
supported by a low friction bearing system inside a housing. A
connected motor/generator accelerates the flywheel for storing
inputted electrical energy, and decelerates the flywheel for
retrieving this energy. Power electronics maintain the flow of
energy into and out of the system, to mitigate power interruptions,
or alternatively, manage peak loads. Traditional flywheel designs
limit their use to the above mentioned short duration applications
due to high electrical parasitic losses associated with
electromagnetic bearing systems.
[0010] One way to support a flywheel for rotation at high speeds is
with rolling element mechanical bearing assemblies such as ball
bearing assemblies. The life of such mechanical bearing assemblies
is strongly influenced by the loads that such mechanical bearing
assemblies must carry. In order to extend the life of flywheel
energy storage systems using mechanical bearing assemblies, a
magnetic bearing can be used in combination with the mechanical
bearings for the purpose of reducing the load on the mechanical
bearings. In such, an, example, the rotor portion of the flywheel
typically rotates about a vertical axis and the mechanical bearing
assemblies provide radial support while the magnetic bearing
assembly carries or supports the axial load of the flywheel.
Traditionally, flywheel designs have utilized electromagnetic
thrust bearings for this purpose.
[0011] U.S. Pat. No. 6,710,489, issued Mar. 23, 2004, (hereinafter
"Gabrys I") discloses the use of a plurality of magnetic bearing
assemblies that are used to support axially the flywheel rotor
portion. Such a flywheel energy storage system also has multiple
mechanical bearing assemblies which each provide radial support for
the flywheel rotor portion, but do not axially restrain the
flywheel rotor portion. The design of such a system having
mechanical bearing assemblies that are unrestrained axially
substantially ensures that the entire axial load of the flywheel or
rotor is distributed on the magnetic bearings, thus reducing the
wear on the mechanical bearing assemblies. In this manner, such a
flywheel rotor portion effectively "floats". The systems of Gabrys
I utilize magnetic bearings to locate the rotor axially, either
repulsive bearings for passive (permanent) magnets, or attractive
bearings for actively controlled electro magnets. Where attractive
bearings are used, a control system is required to adjust the axial
location of the flywheel by adjustment of the attractive force.
Such systems are relatively complex and absorb significant power
while in operation thus limiting their use to short duration
applications.
[0012] U.S. Pat. No. 6,806,605, issued Oct. 19, 2004, (hereinafter
"Gabrys II") also discloses the use of magnetic bearings for
supporting rotating objects. More specifically, Gabrys II discloses
a permanent magnetic thrust bearing with an electromagnetic radial
magnetic bearing having a rotating portion with a circumferential
multi-piece construction. This electromagnetic radial magnetic
bearing provides radial stiffness, which is desirable because
applications wherein a flywheel will, be rotating at high speeds
require that the flywheel be rotating true to its rotational axis.
Thus, Gabrys II discloses a flywheel energy storage system which
uses magnetic forces to produce (i) axial forces that suspend the
flywheel, and (ii) radial forces that centre or stabilize the
flywheel in an effort to maintain a true axis of rotation. Gabrys
II further discloses a flywheel system wherein the flywheel is
axially and radially supported by means of repulsive magnetic
forces that generate a thrust that purportedly maintains a stable
levitation of the flywheel. Repulsive magnetic forces generated
from permanent magnets are known to degenerate over time; and
accordingly there is the possibility of mechanical failure of the
device.
[0013] A paper entitled Low Cost Energy Storage for a Fuel Cell
Powered Transit Bus, authored by C S Hearn describes a flywheel
structure in which passive lift magnets are used to reduce the
axial loads on mechanical bearings. The mechanical bearings axially
locate the rotor of the flywheel. The magnetic path resulting from
the structure shown in Hearn is relatively dispersed, which,
together with the mechanical bearing arrangement disclosed,
provides a relatively inefficient support system.
[0014] It is therefore an object of the present invention to
obviate or mitigate the above disadvantages.
SUMMARY OF THE INVENTION
[0015] In accordance with one aspect of the present invention, an
energy storage system is provided including a first housing having
an end face and a flywheel. The flywheel can have a rotor and a
drive shaft defining a substantially vertical axis about which the
rotor is mounted for rotation within the first housing. The energy
storage system can also include a permanent magnetic bearing
assembly positioned between the end face and the rotor and having a
permanent magnet mounted on the first housing or the rotor, and the
other of the first housing or the rotor having ferromagnetic
properties, to attract the rotor towards the end face. The energy
storage system can further include a first mechanical bearing
assembly acting between the first housing and the rotor to provide
radial positioning of the rotor and to limit upward axial movement
of the rotor in relation to the end face, the rotor being spaced
from the end face by a clearance gap. The energy storage system can
include a second mechanical bearing assembly spaced from the first
mechanical bearing assembly along the drive shaft and acting
between the first housing and the rotor to provide radial
positioning of the rotor, the second mechanical bearing assembly
permitting relative axial movement between the drive shaft and the
first housing.
[0016] In another aspect, an energy storage system is provided that
can include a flywheel housing and a flywheel positioned within the
flywheel housing. The flywheel can include a rotor and a drive
shaft defining a substantially vertical axis about which the rotor
is mounted for rotation within the flywheel housing. The energy
storage system can include a motor/generator housing detachably
attached to the flywheel housing and a motor/generator positioned
within the motor/generator housing. The motor/generator can be
detachably attached to the rotor.
[0017] In a further aspect, an energy storage system is provided
that can include a motor/generator housing, and a motor/generator
positioned within the motor/generator housing. The energy storage
system can include a flywheel housing having a vacuum port and a
flywheel positioned within the flywheel housing The flywheel can
include a rotor, and a drive shaft defining a substantially
vertical axis about which the rotor is mounted for rotation within
the flywheel housing. The energy storage system can include a
vacuum pump connected to the interior volume of the flywheel
housing via the vacuum port. The vacuum pump can be configured to
be energized from electricity supplied by the motor/generator.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] Embodiments of the invention will now be described by way of
example only, with reference to the accompanying drawings, in
which,
[0019] FIG. 1 is a front perspective view of an energy storage
system.
[0020] FIG. 2 is a cross-sectional view along the line II-II of
FIG. 1.
[0021] FIG. 3 is a view similar to that of FIG. 2, in a partly
disassembled state.
[0022] FIG. 3a is a view similar to FIG. 3 further
disassembled.
[0023] FIG. 4 is an enlarged view of an upper portion of FIG.
2.
[0024] FIG. 5 is an enlarged view of a lower portion of FIG. 2.
[0025] FIG. 6a is bottom plan view of a first alternative
embodiment of magnetic thrust bearing assembly.
[0026] FIG. 6b is a cross-sectional view along line 6B-6B of FIG.
6A.
[0027] FIG. 6c is an enlarged view of the encircled area 6C of FIG.
6B.
[0028] FIG. 7a is bottom plan view of a second alternative
embodiment of magnetic thrust bearing assembly.
[0029] FIG. 7b is a cross-sectional view along sight line 7B-7B of
FIG. 7a.
[0030] FIG. 7c is an enlarged view of the encircled area 7C of FIG.
7b.
[0031] FIG. 8 is a plot of an area of FIG. 4, illustrating the
circular magnetic flux pattern created by the magnetic thrust
bearing assembly.
[0032] FIG. 9 is a perspective view of an array of energy storage
systems contained within a collective container, with the
collective container being partially cut away.
[0033] FIG. 10 is a perspective view of an array of collective
containers, each similar to the collective container illustrated in
FIG. 9.
[0034] FIG. 11 is a perspective view of an array of above grade
domed vaults that each house an energy storage system.
[0035] FIG. 12 is a cross-sectional view of an array of below-grade
vaults that each house an energy storage system.
[0036] FIG. 13 is an alternative configuration of energy storage
system.
DETAILED DESCRIPTION OF THE INVENTION
[0037] Although the invention has been described with reference to
certain specific embodiments, various modifications thereof will be
apparent to those skilled in the art without departing from the
spirit and scope of the invention as outlined in the claims
appended hereto. The entire disclosures of all references recited
above are incorporated herein by reference.
[0038] FIG. 1 is a perspective view of an energy storage system 20
that is constructed as a modular system having two major
components: a first housing 21 containing a flywheel (not visible
in FIG. 1) rotatably mounted therein as will be described more
fully below, and a second housing 22 releasably mounted atop the
first housing 21. The second housing 22 contains a motor/generator
(not visible in FIG. 1) coupled to the flywheel to either drive the
flywheel or be driven by the flywheel, upon operation of the system
in a manner that will become more apparent as description
unfolds.
[0039] As best seen in FIG. 1, the first housing 21 has a
cylindrical outer wall 28 that terminates at its upward extent in a
radially outwardly projecting peripheral flange 23, and is closed
at its lower extent by an annular base plate 33. The base plate 33
preferably projects beyond the cylindrical outer wall 28 a radial
distance substantially equal to that of the peripheral flange 23.
The cylindrical outer wall 28 is reinforced at regular intervals
around its circumference by a plurality of spaced vertical ribs 29,
which extend between the base plate 33 and the radially outwardly
projecting peripheral flange 23. The first housing 21 is closed
adjacent its opposite, upper end by means of an annular top plate
27, which is releasably affixed to the radially outwardly
projecting peripheral flange 23 by a plurality of circumferentially
spaced machine screws 31a. Each machine screw 31 a engages a
corresponding plurality of complimentary threaded bores 31b (see
FIG. 2) formed in the radially outwardly projecting peripheral
flange 23. The housing thus formed is of rigid and robust
construction, suitable to contain the flywheel.
[0040] In the embodiment shown, the second housing 22 is formed
with a cylindrical outer wall 2a (of smaller diameter than the
cylindrical outer wall 28 of the first housing 21), which
cylindrical outer wall 22a terminates at its lower extent in a
radially outwardly projecting peripheral flange 64, The second
housing 22 is closed adjacent its upper end by a cylindrical top
plate 35 attached to the cylindrical outer wall 22a by means of,
for example, a plurality of machine screws 37, arranged around the
periphery of the top plate 35 and received in complimentary
threaded bores (not shown) formed in the upper edge of the
cylindrical outer wall 22a.
[0041] It is preferred that the housings 21, 22 are formed from
non-ferromagnetic materials. Non-ferromagnetic materials are
especially preferred for this purpose to minimise the magnetic drag
that slows down the flywheel's rotation and lessens the time the
motor/generator is available for energy release during a discharge
cycle. Suitable materials may be selected from a group including,
but not limited to, stainless steel, aluminum, plastics,
fibreglass, concrete, and combinations thereof, which materials may
also be reinforced with composite materials, including, but not
limited to, carbon fibre, Kevlar.TM., or the like.
[0042] As can be seen in FIGS. 2 and 3, the first housing 21
contains a flywheel 24 that is supported for rotation within the
housing 21 on bearing assemblies 47a, 47b. The flywheel 24 includes
a rotor 25 and an upper drive shaft segment 24a and lower drive
shaft segment 24c segment. The rotor 25 and drive shaft segments
24a, 24c are integrally formed from a forged blank. The rotor 25 is
cylindrical with its axis aligned with drive shaft segments 24a,
24c. The diameters of the drive shaft segments 24a, 24c may differ
due to the different loads applied. The drive shaft segments
24a,24c together define a substantially vertical axis A about which
the rotor 25 is mounted for rotation within the first housing 21 in
a manner that will be described in more detail below. Rotor 25 has
an upper planar end surface 25a and lower planar end surface 25b
with a peripheral surface 25c extending between the upper and lower
planar surfaces. A pair of radial grooves 25d are formed between
the end faces 25a, 25b to facilitate heat transfer during
manufacture. While the first housing 21 may be sized and otherwise
constructed to accommodate more than one flywheel rotating therein,
in the preferred embodiment illustrated, a single flywheel 24 is
shown, as this is the simplest to illustrate and describe, and, as
will become more apparent as this description proceeds, the
preferred arrangement readily supports ordered and regular modular
expansion of the subject energy storage system by adding further
flywheels, one at a time, with each contained within a respective
first housing 21.
[0043] It will also be appreciated that while a solid rotor 25 and
drive shaft 24a, 24b has been described, a fabricated rotor with
separate drive shaft segments may be used. Alternatively, a
separate drive shaft extending through the rotor 25 and attached
thereto for driving rotation thereof could be used.
[0044] The rotor 25 is made from a material having ferromagnetic
properties, such as, for example, high density steel. In alternate
embodiments, other ferromagnetic materials from which the rotor 25
may be manufactured are iron, nickel, cobalt, and the like. The
higher the mass of the rotor 25, the greater the kinetic energy the
energy storage system 20 is able to store at the same RPM of the
flywheel. In contrast, the higher the mass of the rotor 25, the
greater the potential frictional, losses that can occur through the
mechanical bearings used to mount same for rotation, and the
greater the need for precision engineering and robustness of the
system in order to prevent potentially dangerous accidents through
component failure at high RPMs.
[0045] It will be appreciated that the rotor 25 may be made as a
composite structure with part ferromagnetic materials if preferred,
and may be shaped other than cylindrical, provided it is balanced
for high speed rotation. A cylindrical, steel rotor appears to be
the most economical.
[0046] The preferred embodiment illustrated in FIGS. 1 to 5 further
comprises a magnetic thrust bearing assembly 26 that acts between
the housing 21 and flywheel 24 to support a significant portion of
the weight of flywheel 24 thus relieving the mechanical bearing
assemblies 47 of axial loading. The magnetic thrust bearing
assembly 26 has at least one annular permanent magnet 26a that is
mounted on the first housing 21, as described more fully below.
During operation of the preferred embodiment, the annular permanent
magnet 26a remains fixed, and does not rotate, thereby providing a
very stable support mechanism for the flywheel 24 which lies
beneath. The magnetic thrust bearing assembly 26, and more
specifically, the annular permanent magnet 26a, is mounted on the
first housing 21 in stationary centred relation about the vertical
axis A, so as to be juxtaposed with end face 25a of the rotor 25.
The annular permanent magnet 26a may be constructed as a unitary
annulus having a single layer of ferromagnetic metal material, as
shown in FIGS. 2 through 6C, or may vary in its construction, as
discussed further below.
[0047] As the rotor 25 is made from a ferromagnetic material, the
positioning of the permanent magnet above the end face 25a attracts
the rotor 25 axially upwardly towards a lower face 26d of the
annular permanent magnet 26a. The attractive magnetic forces
between the annular permanent magnet 26a and the rotor 25 at least
partially, and ideally, totally, support the weight of the flywheel
24.
[0048] As best seen in FIGS. 2 through 4, magnetic thrust bearing
assembly 26 comprises annular permanent magnet 26a, together with
an annular backing plate 26b and a non-magnetic spacer ring 26c
composed of a non-ferrous metal material, or a polymer, such as
"REANCE F65"--a flexible neodymium iron boron magnet--manufactured
by The Electrodyne Company, Batavia, Ohio. The annular backing
plate 26b is constructed from a ferromagnetic metal, and is mounted
to the underside or end face 21a of the annular top plate 27 of the
first housing 21, also in stationary centered relation about the
vertical axis A. A plurality of machine screws 60 engages
corresponding threaded bores formed in the annular backing plate
26b to secure the backing plate 26b to the top plate 27. The
annular backing plate 26b extends radially beyond the outer radial
edge of the annular permanent magnet 26a, and beyond the outer
radial edge of the non-magnetic spacer ring 26c, to form a
downwardly projecting perimeter skirt portion 61. The downwardly
depending perimeter skirt portion 61 preferably has an outer radius
at least equal to the radius of the rotor 25, with the non-magnetic
spacer ring 26c interposed between the outer radial edge of the
annular permanent magnet 26a and the inner radius of the downwardly
depending perimeter skirt portion 61. The annular backing plate 26b
preferably has a shoulder portion 59 arranged around its outer
circumferential edge, which rests in close-fitting nested relation
upon a complimentary internal annular ledge 65 formed adjacent to
the upper edge of the cylindrical outer wall 28 of the first
housing 21.
[0049] To enhance the support of the rotor 25, the magnetic bearing
26 is configured to constrain the flux path through the rotor 25.
The perimeter skirt portion 61 has a lower face 85 that is
vertically substantially co-terminus with the lower face 26d of the
annular permanent magnet 26a, thereby to also maintain the same
minimum clearance gap 30 between the rotor 25 and the lower face 85
of the perimeter skirt portion 61. The perimeter skirt portion 61
helps shape the magnetic field and thus contributes to the inherent
stability of the rotor 25 while it rotates during operation of the
energy storage system. With the arrangement shown, the annular
permanent magnet 26a, the annular backing plate 26b, the
non-magnetic spacer ring 26c, and the perimeter skirt portion 61
constrain the magnetic flux field to enhance the support capacity
of the bearing 26.
[0050] The annular permanent magnet 26a of FIGS. 2 through 5 is
preferably affixed to the annular backing plate 26b by magnetic
attraction thereto, and such affixation may be supplemented by the
use of low out-gassing adhesive, such as HS-4 Cyanoacrylate
Adhesive manufactured by Satellite City, Simi Valley, Calif., or an
epoxy.
[0051] In the embodiment shown in FIGS. 1-5, the annular permanent
magnet 26a is shown as being formed as a unitary, rigid structure
of conventional magnetized metal, rare earth metal, or the like. In
alternative embodiments, the annular permanent magnet 26a may,
instead, be formed from one or more sections or layers of magnetic
material. This provides, in most cases, for easier and less costly
fabrication. For example, the annular permanent magnet 26a may be
fabricated from a flexible magnetic material, such as rare earth
magnetic particles mixed with a polymer binder (such as is used in
the construction of conventional fridge magnets). In one such
alternative embodiment, shown in FIGS. 6a through 6c, a single
layer of such flexible permanent magnetized material may be formed
from this material in a series of concentric circles 26e of
widening radius wrapped around the vertical axis A in a radially
expanding manner. The magnetic poles of the layer of flexible
magnetic material are aligned in the same direction, and preferably
run in parallel relation to the vertical axis A, as shown by the
arrows in FIG. 6c.
[0052] In a further alternate embodiment (shown in FIGS. 7a through
7c), the annular permanent magnet 26a can be built up from a
plurality of patches 26f of the aforesaid flexible magnetic
material laid in a regular patchwork array having one or more
layers positioned one above the other. As shown in FIGS. 7a through
7c, the patchwork may be of rectangular strips
(1.5''.times.0.125''), and the plurality of layers shown is three
layers 78a, 78b, and 78c. It will again be noted from FIG. 7c that
the magnetic poles of each of the layers 78a, 78b, and 78c of
flexible magnetic material are aligned in the same direction,
preferably running in parallel relation to the vertical axis A.
Patches of flexible magnetic material of other shapes and sizes,
for example, square patches, may be substituted for the rectangular
patches shown in FIGS. 7A through 7C, and the number of layers
utilized in a particular installation will vary according to the
strength required to support the target percentage of weight of the
flywheel 24 to be carried by the magnetic thrust bearing assembly
26 in that particular application.
[0053] Similar forms of affixation may be used for each layer of
permanent magnet material illustrated in the alternate embodiments
illustrated in FIGS. 6a through 6c and 7a through 7c as were
previously described in relation to the embodiment of FIGS. 1
through 5.
[0054] Although the permanent magnet could be formed on the upper
surface of the rotor 25, the stationary mounting of the magnet 26a
permits the use of such flexible permanent magnetic material in the
construction of a magnetic thrust bearing assembly 26. Such
flexible magnetic material is too soft and fragile to sustain high
speed rotation (i.e., above 1,000 RPMs, and more typically above
10,000 RPM) for prolonged periods of time, particularly where the
flexible magnetic material is circumferentially wrapped or laid in
a layered array. By reason of the high centrifugal forces exerted
thereon during high speed rotation the material would be subject to
radial distortion, and possible rupture or de-lamination.
[0055] As illustrated in FIGS. 2 through 4, an electrical rotary
machine that may function as a motor or generator, referred to as a
motor/generator 72 is releasably coupled to the upper drive shaft
segment 24a by means of a coupling shaft 34. The shaft 34 has an
annular collar 34a that projects downwardly from the
motor/generator 72 in order to provide for an axially slidable
engagement with the upper drive shaft segment 24a. The collar 34a
of coupling shaft 34 is releasably coupled to the upper drive shaft
segment 24a by means of a bolt 36. A key 34b and mating keyway
engage one another to operatively connect the coupling shaft 34
with the upper drive shaft segment 24a of the drive shaft for
transfer of torque from the motor/generator 72 to the flywheel 24
(and vice versa). Alternatively, mating splines (not shown) may be
used on the coupling shaft 34 and the upper drive shaft segment
24a, respectively, in place of the key and keyway illustrated.
[0056] The upper mechanical bearing assembly 47a is mounted within
a top portion of the first housing 21, about the upper drive shaft
segment 24a. The upper mechanical bearing assembly 47a provides
axial positioning of the rotor 25 in order to limit at least upward
axial movement of the rotor 25 in relation to the lower face 26d of
the annular permanent magnet 26a. More particularly, the upper
mechanical bearing assembly 47a limits the upward axial movement of
the rotor 25 so as to define a minimum clearance gap 30 between the
lower face 26d of the annular permanent magnet and the end face 25a
of rotor 25. The upper mechanical bearing assembly 47a may also be
preferably configured to limit downward axial movement of the rotor
25 in relation to the lower face 26d of the annular permanent
magnet. In this regard, the upper mechanical bearing assembly 47a
is preferably a thrust bearing. This configuration allows the upper
mechanical bearing assembly 47a to further define a maximum
clearance gap 30 between the lower face of the annular permanent
magnet and the rotor 25, which maximum gap 30 is equal to the
minimum clearance gap 30 in the preferred embodiment illustrated.
Restraining movement of the upper mechanical bearing assembly 47a
in both axial directions assures that the gap 30 maintained between
the lower face 26d of the annular permanent magnet and the rotor 25
is within operative tolerances, thereby assuring reliable lift by
the annular permanent magnet 26a of the rotor 25.
[0057] As best seen in FIG. 4, the upper drive shaft segment 24a
has a precision ground bearing support that terminates at a
shoulder 48. The upper mechanical bearing assembly 47a is
preferably comprised of two rolling element bearing sets 42
contained within a removable bearing cartridge 42a to facilitate
the quick and easy replacement of worn or damaged bearing
assemblies. The rolling element bearing sets 42,42 are both
preferably ceramic angular contact ball bearing sets, and most
preferably very high speed, super precision, hybrid ceramic bearing
sets, meaning, the balls are comprised of ceramic material which
run in precision ground steel races.
[0058] The cartridge 42a includes a bearing support housing 43, a
bearing axial fixing ring 44 and machine screws 45 and 46. The
support housing 43 has a radial flange 43a and a bearing recess
43b. The bearing sets 42 are located in the recess 43b and retained
by the ring 44. The outer races of the rolling element bearing sets
42 are restrained axially between lower surface 44a of bearing
axial fixing ring 44 and end face 49 the bearing recess 43b and the
ring 44 secured by machine screws 45. The bearing support flange 43
is retained axially via machine screws 46 to the upper surface 51
of the annular backing plate 26b, which in turn is fixed to the
annular top plate 27 of the first housing 21 as previously
described.
[0059] The lower surface 34c of collar 34a of coupling shaft 34
bears against the inner races 42b of the rolling element bearing
sets 42 and is secured by a bolt 36 that is received in the drive
shaft 24a. The bolt 36 acts through the shaft 34 to apply a preload
to the rolling element bearing sets 42 by adjustably compressing
the inner races between the lower surface 34c of the coupling shaft
34 and bearing shoulder 48 of the upper drive shaft segment
24a.
[0060] The axial position of the bearing support flange 43 with
respect to the magnetic thrust bearing assembly 26 fixes the axial
position of the upper drive shaft segment 24a of the rotor 25, and
maintains the substantially constant gap 30 between the top surface
25a of the rotor 25 and the lower face 26d of the magnetic thrust
bearing assembly 26. The gap 30 is determinative to applying the
correct lifting force to the rotor 25 and reducing the axial
loading to the rolling element bearing set 42. The gap 30 may be
adjusted by placing shims (not shown) at surface 51 to raise the
bearing support flange 43, thereby lifting the rotor 25 and
decreasing gap 30 to apply a greater magnetic lifting force.
[0061] The lower mechanical bearing assembly 47b, shown in FIG. 5,
acts between the lower drive shaft segment 24c and the housing
bottom plate 33. The lower mechanical bearing assembly 47b has a
pair of rolling element bearing sets 42,42 contained within a
removable bearing cartridge 42a to facilitate the quick and easy
replacement of worn or damaged bearing assemblies. The two rolling
element bearing sets 42, are preferably of the same general type
and construction as the upper mechanical bearing sets (although
they may be of a smaller size due to the lesser mechanical
loading), i.e., they are both preferably ceramic angular contact
ball bearing sets, and most preferably very high speed, super
precision hybrid ceramic bearing sets.
[0062] The cartridge 42a of lower mechanical bearing assembly 47b
further includes bearing support flange 53 having a bearing recess
90. Lower drive shaft segment 24c has a shoulder 89 to locate the
bearings 42 axially. A bearing preload cap 54 is secured by,
bearing preload screw 32, to the lower drive shaft 24c. The bearing
preload cap 54, and bearing, preload screw 32 axially restrain the
inner races of each of the rolling element bearing sets 42,42 and
apply a preload to the rolling element bearing sets 42,42 by
compressing the inner races between an end surface 58 of the
bearing preload cap 54 and the lower bearing shoulder 89 of the
lower drive shaft segment 24c. The outer races 42c of the rolling
element bearing sets 42 are unrestrained axially inside the bearing
recess 90 of lower mechanical bearing assembly 47b. This allows the
lower drive shaft segment 24c of the rotor 25 to move axially as
the rotor 25 contracts axially at high speed due to Poisson Ratio
effects. This also allows for axial movement due to temperature
induced expansion and contraction in both the rotor 25 and the
first housing 21, whilst maintaining the gap substantially
constant.
[0063] The bearing support flange 53 is fixed to base plate 33 of
the first housing 21 by way of machine screws 56. The lower
mechanical bearing assembly 47b also preferably comprises lower
bearing cover 55, which provides, with the assistance of resilient
gasket or O-ring 57, vacuum tight sealing of the lower mechanical
bearing assembly 47b. as well as provides a point to mechanically
support or lock the rotor 25 against axial vibration or movement
during, for example, installation or shipping. A jack screw 57 is
inserted in a threaded hole 40 formed for this purpose in the lower
bearing cap 55 to engage a socket 32a formed in the head of the
bearing preload screw 32. The jack screw 57 supports the rotor both
axially and radially when engaged in the socket to inhibit
transient loads being applied to the bearing assemblies 47.
[0064] In order to minimize the wear on the mechanical bearing
assemblies and in order to minimize friction as the flywheel 24 is
rotating, it is preferable, but not essential, for the magnetic
thrust bearing assembly 26 to support substantially the entire
weight of the flywheel 24. More specifically, it is preferable for
the magnetic thrust bearing assembly 26 to support at least 90% of
the flywheel 24's weight, and more preferably between about 95% and
100% of the flywheel 24's weight. In an ideal situation, the
preferred embodiment, as illustrated, the magnetic thrust bearing
assembly 26 is capable of supporting substantially 100% of the
flywheel's weight. The axial location provided by the upper bearing
assembly 47a, maintains the gap 30 constant, even if the magnetic
bearing assembly 26 provides a lift greater than the weight of the
rotor.
[0065] FIG. 8 illustrates the flux path generated by the magnetic
thrust bearing assembly 26 of FIGS. 2 through 4. As illustrated in
FIG. 8, the flux field 62 is ovoid/circular. However, in three
dimensional representations of the energy storage system 20, the
magnetic flux path is torroidal in shape. As previously discussed,
the downwardly depending perimeter skirt portion 61 helps shape the
magnetic field and thus contributes to the inherent stability of
the rotor 25 while the rotor 25 is rotating during operation of the
energy storage system 20. The annular backing plate 26b and
downwardly depending perimeter skirt portion 61 create a flux field
62 that holds substantially the entire weight of the rotor 25, FIG.
8 illustrates the magnetic flux substantially penetrating the rotor
25 to lift same, and to a lesser extent penetrating the annular
backing plate 26b and downwardly depending perimeter skirt portion
61. The non-magnetic spacer ring 26c inhibits migration of the flux
field from the magnet 26a and facilitates the establishment of the
compact magnetic loop. The non-magnetic wall 28 of the housing 21
also does not interfere with the flux path to enhance the lifting
capacity of the magnetic bearing assembly 26. In a preferred
embodiment the permanent magnet occupies approximately 60% of the
area of the end face 25 indicated at A1, and 40% of the area is the
skirt indicated at A2. Other area ratios may be adopted with a
ratio of 30% the permanent magnetic and 70% the skirt up to 70% of
the permanent magnet and 30% the skirt. Use of backing plate in
this manner allows for 40% less magnetic material and provides
4.times. the lifting force of the magnets alone. Stray flux is
contained, directed into the rotor face and prevented from curving
back down to the rotor sides and causing a significant drag torque
on the system. Additionally, utilizing the large available upper
annular surface area of the rotor facilitates the use of lower
strength, bonded magnetic materials. These materials are lower cost
and easily formable compared to sintered magnets.
[0066] It is preferred that zero electrical energy is required to
be drawn from the power source to which the energy storage system
20 is connected to support the weight of the flywheel 24. This is
achieved through the use of permanent magnetic material in the
construction of the annular permanent magnet 26a. Thus no energy is
consumed by the magnetic thrust bearing assembly 26 in supporting
the weight of the flywheel 24. Moreover, as the magnetic thrust
bearing assembly 26 is mounted to the first housing 21, the weight
of the flywheel 24 is supported by attractive forces of the
magnetic thrust bearing assembly 26, which is itself supported by
the cylindrical outer wall 28 of the first housing 21, which is, in
turn, supported by the base plate 33 of the first housing 21.
[0067] In the preferred embodiment illustrated in FIGS. 1 through
5, the energy storage system 20 is made more efficient by
minimizing the frictional forces which might otherwise act directly
on the rotor 25 as it rotates. Accordingly, the rotor 25 should not
come into contact during rotation with the any of the internal
surfaces projecting into the first housing 21, including the lower
face 26d of the magnetic thrust bearing assembly 26. To this end,
it has been described above how the gap 30 between the top surface
25a of the rotor portion 25 and the lower faces 26d and 85 of the
annular permanent magnet 26a and the downwardly depending perimeter
skirt portion 61, respectively, are maintained. To the same end, a
minimum clearance gap 70 is at all times defined between the outer
circumferential edge 25c of rotor 25 and the internal surface 82 of
first housing 21. Similarly, the components within the first
housing 21 are shaped and otherwise dimensioned to maintain at all
times a minimum clearance gap 75 between the lower surface 25b of
the rotor 25 and the upper internal surface 98 of the base plate
33.
[0068] To further reduce and substantially eliminate drag forces
acting on the rotor 25 during operation (i.e., while the flywheel
24 is rotating), it is desirable to reduce windage losses on the
rotating components by drawing at least a partial vacuum within at
least the first housing 21, and preferably within both the first
housing 21, and second housing 22. To this end, it is preferred to
seal both the first 21 and second 22 housings to atmosphere by, for
example, the placement of resilient gaskets or O-rings 86,57 in
operative sealing relation around all mating joints of the
components of the two housings 21,22, including, without
limitation, between the wall components 27,28 and 33 of the first
21 and second 22 housings, and between the bearing preload cap 54
and the bearing support flange 53, as best seen in FIGS. 2, 4 and
5.
[0069] A vacuum source, such as a conventional vacuum pump 91, is
preferably connected by flexible tubing or the like to the interior
volume of the first housing 21 by connection to, for example, a
vacuum port 87 attached to, or formed in, for example, the base
plate 33, so as to be in fluid communication with the gaps 30,70
and 75, thereby to allow for the drawing of at least a partial
vacuum within the first housing 21 upon operation of the vacuum
pump.
[0070] It is also preferable, though not essential, to operatively
connect a vacuum source, being preferably the same vacuum source
mentioned in the previous paragraph, but optionally being a second
vacuum source (not shown), to the second housing 22 to also create
an at least partial vacuum in the second housing 22, thereby to
reduce frictional, losses that would otherwise occur upon rotation
of components of the motor/generator 72. A particularly preferred
manner of introducing such an at least partial vacuum initially
created in the first housing 21 into the second housing 22 without
the need for a second vacuum source, is by providing for a vacuum
passageway to be established between the first housing 21 and
second housing 22 when assembled together as shown in the figures.
As seen in FIG. 4, a vacuum passageway 187 extends in fluid
communication through the coupling shaft 34, the key 34b and the
keyway 34b, around the inner races 42b of the two rolling element
bearing sets 42 of the upper mechanical bearing assembly 47a,
downwardly past the inner radial surface of the bearing support
flange 43, to connect with a radial channel 50. Channel 50
surrounds the basal connection point of the upper drive shaft
segment 24a to the rotor 25. The radial channel is itself in fluid
connection with the gap 30. In this manner, the vacuum, source
operatively connected to the first housing 21 is also operatively
connected to the second housing 22 through vacuum passageway 187
upon mounting of the second housing 22 atop the first housing
21.
[0071] The vacuum pump 91 is preferably energized from electricity
drawn from the electrical power grid to which the energy storage
system 20 is connected during its charging phase, but may, or may
not, depending upon design choice, be energized from electricity
supplied by the motor/generator 72 during periods when the
electrical grid is not available to supply such electrical energy.
In either case, the sealing of the first 21 and second 22 housings
should ideally, but not essentially, be designed and built to
sustain said at least partial vacuum over the full design period of
rotation of the rotor 25 during de-energization of the
motor/generator 72, so as to minimize drag forces acting on the
rotor 25 during such periods. To minimize energy consumption, the
vacuum pump 91 may be controlled to switch off when a partial
vacuum is drawn with a check valve 92 to inhibit leakage in to the
housing 20.
[0072] The motor/generator 72 is connected to an external
electrical power source so as to enable the motor/generator 72 to
draw electrical energy from an electrical power source, such as an
electrical power grid, when the connection is energized. The
motor/generator 72 draws electrical energy from the electrical
power grid in order to drive rotation of the rotor 25. The driving
of the rotor 25 by the motor/generator 72 effectively converts the
electrical energy inputted into the system into kinetic energy that
is stored in the rotation of the rotor 25 of the flywheel 24. The
kinetic energy stored in the rotation of the rotor 25 is thus
stored in the energy storage system 20 for reconversion to
electrical energy and release of the electrical energy during
rotation of the motor/generator by the flywheel 24, when the
connection is de-energized.
[0073] According to the preferred embodiment illustrated, the
second housing 22, having the motor/generator 72 mounted therein,
is releasably mounted atop the first housing 21. The modular
construction of the energy storage system 20 allows the
charge/discharge power used and generated by it to be readily
altered without redesigning or disassembling the entire system by
increasing/decreasing the motor/generator 72 size on any given
energy storage system 20. FIG. 3 illustrates the motor/generator 72
being connected to the upper drive shaft segment 24a in a
releasable manner through coupling shaft 34 as described above. The
second housing 22 is connected to the first housing 21 in a
releasable manner by bolts passing through the flange 64 and in to
the annular backing plate 26b, It will be noted that the coupling
does not affect the positioning of the bearing assembly 47a,
thereby maintaining the required clearance between the rotor 25 and
the magnetic bearing assembly 26. By virtue of the releasable
coupling of the motor/generator 72 to the upper drive shaft segment
24a and the releasable coupling of the second housing 22 (in which
the motor/generator is mounted) to the first housing 21, the energy
storage system 20 is effectively constructed or assembled in a
modular manner so as to facilitate the replacement of worn or
damaged parts, or the interchanging of motors/generators having a
particular desired power rating in order to more effectively or
efficiently store and discharge electricity in accordance with a
predetermined criteria. The modular nature of the preferred
embodiment illustrated in FIG. 3 facilitates varying the ratings or
power specifications of the motor/generator once the flywheel
energy storage system has been manufactured. It is also preferable,
but not essential, that the second housing 22 and the
motor/generator 72 mounted therein are readily removable and
interchangeable without the need for disassembly of the first
housing 21 or any of the structures contained therewithin.
Accordingly, modular construction of the energy storage system 20
as illustrated and described herein allows the charge/discharge
power ratings of the energy storage system 20 to be readily altered
or customized by increasing/decreasing the motor/generator size or
type on any given energy storage system 20. This flexibly allows an
energy storage system 20 having the same flywheel stored energy
capacity (e.g. 20 kWH) to be utilized either for Long Duration, Low
Power (e.g. Peak Shifting/Time of Use) or Short Duration, High
Power (e.g. Voltage Support) applications with only quick and easy
swapping out of a different motor/generator unit mounted within
interchangeable second housings.
[0074] In the preferred embodiment illustrated in FIGS. 1 through
5, the motor/generator 72 shown is an induction type
motor/generator 72. More particularly, the preferred
motor/generator 72 illustrated is preferably a three-phase
induction type unit, which is comprised of a rotor 74, press fit
onto the coupling shaft 34, and a stator winding 76, pressed into
the inside circumference of the cylindrical outer wall 22a of the
second housing 22.
[0075] As illustrated in FIGS. 1 through 4, the motor/generator 72
is preferably liquid cooled, such that the second housing 22 also
preferably includes a coolant jacket comprised of a main coolant
channel 80 encircling the outer surface of the cylindrical outer
wall 22a of the second housing 22, said main coolant channel 80
being enclosed on its outer periphery by a removable outer shell
88. O-ring seals 81 assist in sealing the removable outer shell 88
to the cylindrical outer wall 22a of the second housing 22. Coolant
flows into ingress port 38, passes through the main coolant channel
80, and then outward through egress port 39. The coolant flow can
be via an external pump, or natural convection (in which case the
ingress 38 and egress 39 ports are beneficially reversed from the
arrangement shown) in order to the remove waste heat from the
second housing 22 and the stator winding 76.
[0076] Electrical cable connections to the motor/generator 72 are
preferably made through the top plate 35 at port 41, which port
should be made vacuum tight around such connections by rubber
grommets, O-ring seals and the like (not shown).
[0077] It will be appreciated that the rotor 25 is, as shown in the
figures, solid and comprised of high strength steel. At least a
portion of the rotor 25 must be ferromagnetic in order to interact
with the magnetic thrust bearing assembly 26. Preferably, at least
an upper portion of the rotor opposite the bearing assembly 26 is
magnetic, and, as a further preference, the entire rotor 25 is
ferromagnetic. It may preferable in some embodiments of the energy
storage system 20 for the rotor 25 to have a mass between about
1,000 kg and 5,000 kg with 3,000 kg a preferred mass.
[0078] In operation, power is supplied to the rotor/generator 72
which applies a torque to accelerate the rotor 25. It is
preferable, but not essential, that the motor/generator 72 be
capable of rotating the rotor 25 at high speed, between about
10,000 and 20,000 RPM. As the rotor 25 accelerates, it stores the
energy supplied by the rotor/generator 72 as kinetic energy. Upon
attainment of the maximum speed, the electrical power may be
disconnected. In a typical implementation, the maximum rotation
speed of the rotor 25 is obtained within 2 hours of the electrical
connection to the motor/generator 72 being energized by the power
grid. It also be preferable, but not essential, that such high
speed rotation of the rotor 25 continue for at least 6 hours
following the electrical connection to, the power grid being
de-energized. If the power is disconnected, or if additional
electrical energy is required by the grid, the motor/generator is
switched to a generating mode and the energy stored in rotor 25
drives the generator and supplies electrical power. In some
embodiments, the storage capacity of the energy storage system 20
is approximately 20 kWh. The energy storage is a function of the
weight of the flywheel and the speed at which the flywheel 24 is
rotated. During rotation the gap 30 is maintained by the bearing
assembly 47a. Changes in axial dimensions, due to thermal changes
or dynamic forces, is accommodated in the lower bearing 47b which
may slide axially relative to the end plate 33. The flux path
described in FIG. 8 ensures the rotor 25 is maintained axially by
the magnetic bearing and accordingly, the axial loads in the
bearings 47a, 47b are reduced.
[0079] Because of the relationship between an energy storage
system's 20 energy storage limitations and an energy storage
systems' 20 inherent size and weight, it may be advantageous and
preferable in some applications to use, or otherwise require the
use of a plurality of smaller energy storage systems 20 in favour
of a lesser number of large energy storage system 20 constructed
according to the preferred embodiment. An array of relatively
smaller energy storage systems 20 allows for users to store a
greater amount of energy in the form of kinetic energy whilst
maintaining ease of deployment and greater flexibility to
accommodate for electrical power requirements of different scales
in particular applications. In such situations, it may be
preferable that the array of energy storage systems be controlled
by a common control unit. Further, it may be even more preferable
that the common control unit controls the electrical energy draw
and the release of energy from each of the energy storage systems
20 in the array of energy storage systems. For some commercial
embodiments, it may be preferable to have an array of energy
storage systems having a collective energy output of at least 500
kWh.
[0080] In this regard, FIG. 9 illustrates an array 100 of energy
storage systems 120, 220, 320, and 420 being contained within a
collective container 101.
[0081] FIG. 10 illustrates an array or a plurality of collective
containers 101, 201, 301, 401 each of which contains an array of
energy storage systems 120, 220, 320, etc.
[0082] FIG. 11 illustrates an array of domed vaults 102, 202, 302,
and 402. Each of the vaults is above grade and houses an energy
storage system 120 therewithin. Similarly, FIG. 12 illustrates in
section an array of concrete vaults 102, 202, 302, 402, and 502.
Each of the vaults 102, 202, 302, 402, and 502 may be located
below-grade, and each houses an energy storage system 120, 220,
320, etc., respectively.
[0083] The provision of the flywheel support with one of the
bearing assemblies axially locating the shaft and the other bearing
permitting the drive shaft to float axially facilitates alternative
configurations of rotor. As shown in FIG. 13, the rotor 25 is
formed with ancillary rotor discs, 125 spaced along the drive shaft
24a.
[0084] Each of the discs 125 has an upper face 127 directed toward
a respective permanent magnet thrust bearing 126 which is located
within the housing 21. Upper bearing assemblies 147 axially locate
the rotor 25 with a lower bearing assembly 147 radially permitting
relative axial movement.
[0085] The discs 125 are formed from a ferromagnetic material and
the thrust bearings 126 have a similar configuration to the thrust
bearing shown in FIG. 4, with an annular permanent magnet and a
surrounding skirt overlapping the discs.
[0086] The magnetic thrust bearings attract respective ones of the
discs 125 to support the mass of the rotor 25, as described
above.
[0087] It will be appreciated that the array of discs 125 may be
formed on the lower drive shaft 24c to support the rotor from
beneath by attraction.
[0088] Various other modifications and alterations may be used in
the design and manufacture of the energy storage system according
to the present invention without departing from the spirit and
scope of the invention, which is limited only by the accompanying
claims. For example, separate and apart from the use of the liquid
cooling means illustrated in the Figures, the second housing 22
could additionally be fabricated with external cooling fins for
convective or forced air cooling to the ambient atmosphere.
* * * * *