(12) United States Patent
`Hockney et al.
`
`US006262505B1
`(10) Patent N0.:
`US 6,262,505 B1
`(45) Date of Patent:
`*Jul. 17, 2001
`
`(54) FLYWHEEL POWER SUPPLY HAVING
`AXIAL MAGNETIC BEARING FOR
`FRICTIONLESS ROTATION
`
`_
`-
`_
`(75) Inventors‘ Rlchard L‘ Hockney’ Lynn?eld’_
`Stephen B‘ Nlchols’ charlestowna
`Geo?fey B- lfansberry’ Cambndge}
`Francls E- Nlmblétt, Bevérly; Darlusl
`A.Bushk0,H0pk1nt0n;G1ta P- R210,
`Belmont; Luka Serdar, Lexington;
`Michael E. Amara], NorWood; William
`E. Stanton, Waltham; James
`O’Rourke, Woburn, all of MA (US)
`
`(73) Assigneei SatCOIl Technology Corporatiolh
`Cambridge, MA (US)
`
`(*) Notice:
`
`This patent issued on a continued pros
`ecution appllcatior} ?led under 37 CFR
`1-53(d), and 1s subtect to the twenty year
`patent term provisions of 35 U.S.C.
`154(a)(2).
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`(21) Appl. No.: 08/824,862
`(22) Filed;
`Mar, 26, 1997
`
`7
`
`9/1985 Becker ................................. .. 415/90
`4,541,772
`4,860,611 * 8/1989 Flanagan et a1.
`74/574
`5,126,610 * 6/1992 Fremerey ...... ..
`.310/90.5
`5,212,419 * 5/1993 Fisher et a1. .
`. 310/254
`5,436,512 * 7/1995 Inam etal.
`..... .. 307/58
`5,521,448 * 5/1996 TecZa et a1. .
`310/90.5
`5,548,170 * 8/1996 ShultZ ....... ..
`310/90.5
`5,559,381 * 9/1996 Bosley et a1.
`310/34
`5,628,232
`5/1997 Bakholdin et a1.
`74/572
`5,682,071 * 10/1997 Buhler et a1.
`310/90.5
`5,708,312
`1/1998 Rosen et a1. .
`..... .. 310/90
`5,749,700 * 5/1998 Henry et a1. ....................... .. 415/104
`
`FOREIGN PATENT DOCUMENTS
`
`58-65321 * 41983 JP ..
`.310 90.5
`8-275444 * 10/1996 (JP) ...................................... .. 31/0/74
`
`OTHER PUBLICATIONS
`
`“Design of Brushless Permanent—Magnet Motors”; Hender
`shot and Miller; pp. 2—2, 2—4, 45, 6—41, 1994*
`
`* cited by examiner
`
`Primary Examiner—Karl Tamai
`(74) Attorney, Agent, or Firm—Dike, Bronstein, Roberts &
`Cushman, Intellectual Property Practice Group; George W.
`Meuner
`
`ABSTRACT
`(57)
`A poWer supply device for providing uninterrupted poWer
`for a period of time is disclosed. The poWer supply device
`
`. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..
`
`a
`
`a
`
`~~ 310/ 90-5; 74/574; 310/51
`(52) US Cl- ~~~~~~~~~~~~~~~~ --
`(58) Field Of Search ............................. .. 310/74, 90.5, 51;
`74/572, 574, 5-46; 244/165, 166
`_
`References Clted
`Us PATENT DOCUMENTS
`
`(56)
`
`3,323,763 * 6/1967
`3,860,300 * 1/1975
`3,874,778
`4/1975
`3,955,858
`5/1976
`4,285,251 * 8/1981
`4,444,444 * 4/1984
`
`has a housing that contains a ?ywheel rotor and a motor/
`generator rotor, The ?ywheel rotor and the motor/generator
`rotor are mounted on a common shaft. An active axial
`magnetic bearing is located to support the shaft for friction
`less rotation. The bearing provides support for the shaft, the
`?ywheel rotor and motor/ generator rotor. The axial magnetic
`bearing is attached to the housing and provides, in combi
`nation With the motor/generator rotor, a ?ux path and
`magnetic ?eld to exert a magnetic force to lift the motor/
`generator rotor and the shaft on Which it is mounted.
`
`40 Claims, 10 Drawing Sheets
`
`TEMP 1008
`IPR of U.S. Pat. No. 8,008,804
`
`0001
`
`

`

`US. Patent
`U.S. Patent
`
`Jul. 17, 2001
`Jul. 17, 2001
`
`Sheet 1 0f 10
`Sheet 1 0f 10
`
`US 6,262,505 B1
`US 6,262,505 B1
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`

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`U.S. Patent
`
`Jul. 17, 2001
`
`Sheet 2 0f 10
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`US 6,262,505 B1
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`US. Patent
`
`Jul. 17, 2001
`
`Sheet 3 0f 10
`
`US 6,262,505 B1
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`US. Patent
`
`Jul. 17, 2001
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`US 6,262,505 B1
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`US. Patent
`
`Jul. 17, 2001
`
`Sheet 5 0f 10
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`US 6,262,505 B1
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`US. Patent
`U.S. Patent
`
`Jul. 17, 2001
`Jul. 17, 2001
`
`Sheet 6 6f 10
`Sheet 6 0f 10
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`US 6,262,505 B1
`US 6,262,505 B1
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`US. Patent
`
`Jul. 17, 2001
`
`Sheet 7 0f 10
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`US 6,262,505 B1
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`

`

`U.S. Patent
`
`Jul. 17, 2001
`
`Sheet 8 0f 10
`
`US 6,262,505 B1
`
`Axial Gop
`Position
`Sensor
`
`—-—-——>-
`
`t
`Com
`penso or
`
`,
`Vonugem
`Currem,
`Ampli?er
`
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`Position
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`BottomY ———>x2
`
`+
`
`Balance
`Monitoring
`
`FIGIO
`
`0009
`
`

`

`U.S. Patent
`
`Jul. 17, 2001
`
`Sheet 9 0f 10
`
`US 6,262,505 B1
`
`Charge State
`
`L'- Standby State
`
`p
`_ Generate State
`
`,7
`
`,_ Shutdown State
`
`'
`
`Selftest State
`
`Faulted State
`
`0010
`
`

`

`U.S. Patent
`
`Jul. 17, 2001
`
`Sheet 10 0f 10
`
`US 6,262,505 B1
`
`Utility
`
`+
`
`A _
`
`D C Bus
`
`Current |
`Sense
`
`I Voltage
`L Sense
`
`Discharge/
`Charge
`Control
`
`P W M
`'-> inverter
`
`l
`
`Shutdown
`' _i‘
`
`-=
`
`3Phase
`VFAC
`
`Monitor / Self
`Diagnostics
`A
`
`Commutation
`Signals
`
`Sensor Signals
`
`Flywheel
`Mo'dule
`Position Sensing
`
`Current Mag Bearing
`Control
`4
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`
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`
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`Diagnostics
`
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`Signals
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`
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`
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`Control
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`
`F I G I 2
`
`'
`
`0011
`
`

`

`US 6,262,505 B1
`
`1
`FLYWHEEL POWER SUPPLY HAVING
`AXIAL MAGNETIC BEARING FOR
`FRICTIONLESS ROTATION
`
`FIELD OF THE INVENTION
`
`This invention relates to uninterruptible power supply
`systems and particularly to ?ywheel systems. More
`particularly, the invention relates to a magnetic levitation
`?yWheel 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 ?ber
`from the central of?ce 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 con?guration,
`Where signals are sent from the “head end” (cable company
`of?ce) 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 ?ber 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 “main
`tenance free,” the batteries need continuous on-site moni
`toring and maintenance. The performance and life of bat
`teries 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 ?ve 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 envi
`ronmental and safety regulations.
`One replacement for batteries is the ?yWheel energy
`storage system. Existing systems for supporting high speed
`?yWheels 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
`?yWheel 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 ?yWheel. 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 combin
`ing active and passive control.
`US. 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
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`2
`structure limits speed due to stress. The current of the
`Winding is sWitched electronically by an amplitude modu
`lation system, associated to a reactance coef?cient 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 ?yWheel. This system requires com
`bining tWo control coils With tWo rotating permanent mag
`nets for each bearing.
`It can be appreciated that neW and improved magnetic
`levitation ?yWheel 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 levita
`tion ?yWheel module. The ?yWheel module comprises a
`?yWheel rotor contained in a vacuum housing. The ?yWheel
`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 ?yWheel module. The
`controller is con?gured to provide initial charge up of the
`?yWheel to bring it up to standby speed, to keep the
`?yWheel, speed Within a predetermined range at standby, to
`provide a predetermined voltage to the system for uninter
`rupted poWer supply, and to monitor the status of the
`?yWheel module.
`The ?yWheel module comprises a vacuum housing. In the
`housing is a ?yWheel and a motor/generator. The ?yWheel
`rotor and the motor/generator rotor are mounted on a com
`mon 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
`?yWheel and the motor/generator. The axial magnetic bear
`ing is attached to the housing and provides, in combination
`With the motor/generator rotor, a ?ux path and magnetic ?eld
`that provides a magnetic force to lift the motor/generator
`rotor and the shaft on Which it is mounted.
`More particularly, the ?yWheel module comprises a ver
`tical shaft on Which the ?yWheel 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. Amotor stator is ?xedly 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 of?oads 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
`
`0012
`
`

`

`US 6,262,505 B1
`
`3
`a sleeve positioned in the center bore and ?tting around the
`shaft. The plate member has a chamber for containing a
`damping ?uid. The chamber communicates With the center
`bore by means of a bore hole for ?uid passage therebetWeen.
`The chamber also contains a spring and a plug, the plug
`being located betWeen the spring and the ?uid to transfer a
`force from the spring to the ?uid or the ?uid 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 ?yWheel rotor to its
`steady state speed, transforming electrical energy into
`kinetic energy. The ?yWheel 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 ?yWheel for delivery to the bus.
`The ?yWheel energy storage system (FESS) of the present
`invention can provide a “plug for plug” replacement for
`batteries in telecommunications remote poWering applica
`tions such as vaults, huts and cabinets.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is an elevational vieW, partly in cross-section, of a
`?yWheel module in accord With one embodiment of the
`present invention.
`FIG. 2 is a block diagram illustrating the operation of an
`aXial magnetic bearing in a ?yWheel device in accord With
`one embodiment of the present invention.
`FIG. 3 is an elevational vieW of a ?yWheel module in
`accord With a preferred embodiment of the present inven
`tion.
`FIG. 4 is a partial cross sectional vieW illustrating further
`detail of the motor/generator assembly, top end radial mag
`netic bearing and damping system of the ?yWheel module
`illustrated in FIG. 3.
`FIG. 5 is a cross sectional vieW illustrating further detail
`of the top end damping system for the ?yWheel module
`illustrated in FIG. 3.
`FIG. 6A is a plan vieW of an alternative damper for the
`?yWheel module illustrated in FIG. 3.
`FIG. 6B is a cross sectional side vieW of the alternative
`damper for the ?yWheel module illustrated in FIG. 6A.
`FIG. 7 is a cross sectional vieW in further detail of the
`bottom end radial magnetic bearing and damping system for
`the ?yWheel module illustrated in FIG. 3.
`FIG. 8 is a block diagram illustrating a control system for
`a ?yWheel module of the present invention.
`FIG. 9 is a block diagram illustrating the operation of the
`aXial magnetic bearing.
`FIG. 10 is a block diagram illustrating a system for
`detecting the balance status of a ?yWheel module of the
`present invention.
`FIG. 11 is a state transition diagram for a controller for a
`?yWheel module of the present invention.
`FIG. 12 is a block diagram illustrating a control system
`for a plurality of ?yWheels of the present invention.
`
`10
`
`15
`
`25
`
`35
`
`45
`
`55
`
`DETAILED DESCRIPTION OF THE
`INVENTION INCLUDING PREFERRED
`EMBODIMENTS
`A preferred ?yWheel device in accord With the present
`invention Will be described With reference to the draWings.
`As illustrated in FIG. 1, a preferred ?yWheel device is
`
`65
`
`4
`con?gured as a module. A housing 45 contains the ?yWheel
`15 Which is suspended in the housing. The ?yWheel 15 is
`made With a ?yWheel rotor rim 16 Which is an energy storage
`rim. The ?yWheel rotor rim 16 is mounted on a hub 17 Which
`rotates at one and of an shaft 18. The module can be
`suspended from pins 40 to provide one aXis of a tWo aXis
`gimbal suspension.
`A permanent magnet motor/generator 80 is located near
`one end of the shaft and an aXial magnetic bearing 50 is
`located adjacent the motor/generator. The housing 45 sur
`rounds the ?yWheel and preferably contains a vacuum With
`the vacuum level maintained by an ion pump (not shoWn).
`In a preferred embodiment, a ?yWheel module 10 is
`constructed as illustrated in FIG. 3. A vacuum housing
`comprising housing cylinder 145, top cover 146 and bottom
`cover 147 surrounds the ?yWheel rotor 115. The ?yWheel
`rotor is mounted on a cylindrical support tube 116, Which in
`turn is mounted on the vertical shaft 118. At the top of the
`cylindrical support tube 116 is positioned the motor/
`generator 180, a portion of Which is conveniently used to
`mount the cylindrical support tube at its top end on the shaft.
`The motor/generator assembly 180 is illustrated in further
`detail in FIG. 4. The motor/generator rotor is provided in
`tWo parts; an outer rotor cup 182 and an inner rotor cup 184,
`both of Which are preferably made of iron and mounted on
`shaft 118 and Which act as the return ?uX path for radially
`polariZed permanent magnet pole pieces 187, 188. The stator
`190 is con?gured With a L-shaped cross section and is
`?Xedly mounted to the top cover 146. The outer rotor cup
`182 is con?gured at its top end to receive and hold the
`cylindrical support tube 116.
`On top of and adjacent to the inner rotor cup 184 is ?Xedly
`mounted an active magnetic bearing 120 having a coil 121
`Wound around an inner ferromagnetic core member 124 and
`sandWiched betWeen the inner core member and an outer
`ferromagnetic ?uX member 125. The inner rotor cup 184 is
`made also of a ferromagnetic material. Thus, When a current
`is applied to the coil 121, a magnetic ?uX path is established
`through the inner ferromagnetic core member 124, the outer
`ferromagnetic ?uX member 125 and the ferromagnetic inner
`rotor cup 184 and an aXial magnetic force is eXerted on the
`shaft 118 through the inner rotor cup.
`Radially polariZed permanent magnets 187,188 are
`mounted to the outer rotor cup as alternately polariZed pole
`pieces. As an alternative, a single roW of radially polariZed
`magnets can be used.
`At the top end of the shaft 118 is a touchdoWn bearing
`comprising magnetic bearing assembly 150 and an annulus
`158 providing a radial touchdoWn bearing, and a hardened
`surface 160 at the end of the shaft With a touchdoWn button
`161 located in the top cover 146 assembly (see FIG. 4).
`Preferably, the annulus 158 and button 161 are made of a
`polyimide material, or the like. Also, in the top cover
`assembly is a damping system 130 (see FIGS. 4,5). An end
`plate 100 is mounted on top of the top cover 146. The end
`plate holds a ?Xed center rod 95 at the end of Which is
`mounted touchdoWn button 161. A spring 98 is positioned
`Within the end plate to provide an aXial preload force. The
`spring engages sleeve 135 in Which the end of shaft 118
`rotates in ball bearing 136.
`The magnetic bearing assembly 150 is a passive combi
`nation aXial/radial magnetic bearing. A portion mounted to
`the shaft 118 comprises a cup member 151, preferably made
`of titanium, Which is spaced axially from the inner rotor cup
`184 by a spacer member 128. The cup member 151 is held
`in place by a retainer nut 152 threaded on the end of the shaft
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`118. Inside the cup Wall is ?xed an axially polarized per
`manent magnet 155, Which is held by suitable means such as
`epoxy. A second axially polarized permanent magnet 156 is
`?xedly mounted above the magnet 155. Both are polariZed
`so the magnets attract, providing passive axial support for a
`portion of the Weight of the rotor, preferably at least about
`70%. The magnets in axial attraction also provide radial
`stabiliZation for the shaft 118. The permanent magnets
`155,156 can be multiple annular rings of permanent magnet
`material.
`The damping system 130 (see FIG. 5), preferably com
`prises a plate member 131 that attaches to top cover 146. A
`cylindrical sleeve 135 is positioned Within a center bore in
`the plate member 131. An annulus 158 providing a radial
`touchdoWn bearing is held in the plate member 131 by pins
`159. O-rings 132,133 provide a seal for the annular space
`betWeen the cylindrical sleeve 135 and the bore Wall. Aball
`bearing 136 is mounted Within the sleeve to receive the top
`end of shaft 118. A chamber 140 is located in the plate
`member 131 in proximity to the central bore. A bore hole
`141 communicates betWeen the chamber 140 and the annu
`lar space betWeen the cylindrical sleeve 135 and the bore
`Wall. The chamber and annular space are ?lled With a
`damping ?uid to damp radial vibration at the end of the shaft
`118. In the chamber 140 is a plug 139 Which exerts pressure
`on the damping ?uid due to spring 138. The spring is held
`in place by damper cover 137. The plug 139 has o-rings
`143,144 to provide a seal With the chamber Wall. To provide
`damping ?uid uniformly around sleeve 135, one or more
`additional bores 148 are used as ?uid reservoirs and com
`municate through bore holes 149 to the annular space.
`As an alternative, an elastomeric damper 200 can also be
`used to dampen radial vibration at the end of the shaft (see
`FIGS. 6A—6B). The elastomeric damper 200 is an annular
`ring of elastomeric material preferably betWeen tWo rings
`201,202 made of a non magnetic, hard material as shoWn in
`FIGS. 6A—6B. The sleeve 135 is positioned in the center
`hole 204 and the damper is ?xedly mounted Within the plate
`member 131. Preferably, the damper has spaces formed
`Within the ring to set the amount of damping, e.g., annular
`spaces 205.
`The bottom end of the shaft 118 also has a passive,
`combination axial/radial magnetic bearing, a touchdoWn
`bearing, and a damping system, similar to the top end. With
`reference to FIG. 7, the bottom of the ?yWheel 115 is held
`in place by cap 220 Which is mounted on shaft 118 and
`engages tube 116. The loWer passive axial bearing 230 is
`formed by a housing 231 that is mounted on the loWer cover
`147. Inside the housing is mounted an axially polariZed
`permanent magnet 235 Which is separated from the housing
`by a non-magnetic stainless steel spacer 232. Beneath the
`magnet 235 is positioned a second axially polariZed magnet
`236 Which is ?xedly mounted in a cap 241 Which, in turn, is
`mounted on the shaft 118. Retainer nut 242 holds the cap 241
`in place axially.
`The damping system and touchdoWn bearing at the loWer
`end are con?gured similarly to those at the top end as
`illustrated in FIG. 7. Many of the components are essentially
`duplicates of those used at the top end, as illustrated.
`The ?yWheel energy storage rim is made preferably from
`a glass or carbon ?ber composite With epoxy matrix, or the
`like. The rim for a 2 kW-hr ?yWheel poWer supply that can
`supply 1.0 kW of continuous poWer Weighs approximately
`100 lbs and is attached to the shaft using a lightWeight hub
`structure. Such rim stores a total of 2,600 W-hr at its design
`speed of 30,000 RPM. Preferably, the rim material Will
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`permit the ?yWheel to operate at temperatures up to 85° C.
`Without degradation in performance or cycle life.
`The axial magnetic bearing is an active magnetic bearing
`Which is off-loaded using the permanent magnets of the
`passive radial magnetic bearings for loW loss operation. A
`polyimide annulus is employed, preferably, as a radial
`touchdoWn bearing for the radial magnetic bearing in the
`event of a shock or seismic occurrence Which exceeds the
`capability of the magnetic bearings. The radial touchdoWn
`bearing is not for long-term operation. The touchdoWn
`bearing in the axial direction is provided via hardened
`surfaces preferably combined With a polyimide button.
`The general operation of the active magnetic axial bearing
`can be described as folloWs (see FIG. 2). The magnetic
`bearing is a position control loop Which uses a magnetic
`actuator as the force generator. The applied force on the
`mass results in a displacement Which is sensed using an axial
`position sensor. The sensed position, represented as a
`voltage, is compared to a reference position and the error is
`fed to the loop compensation Which calculates the force to
`be commanded from the actuator and sends the signal to the
`poWer ampli?er Which produces the appropriate current in
`the actuator. The actuator then changes the applied force
`resulting in a closed loop system.
`An integral 2-axis gimbal assembly is used preferably to
`maintain the vertical orientation of the spinning shaft despite
`variations in local ground inclination due to such affects as
`frost heaves and earthquake.
`The motor/generator Which performs the bi-directional
`electromechanical energy conversion is a preferably a per
`manent magnet (“PM”) brushless design. Preferably, it uses
`neodymium boron iron magnets in a 4 or 6 pole con?gura
`tion. Preferable, the con?guration is structured to achieve
`greater than 96% efficiency When averaged over a complete
`charge/discharge cycle.
`The control system is described With reference to FIG. 8.
`The DC bus of the ?yWheel module and control in accord
`With the present invention can be connected to the battery
`terminals of a conventional standby poWer control unit such
`as, for example, the Alpha Technology model XM 6015
`poWer supply unit. The electronics for the ?yWheel is
`conveniently packaged as an electronics module. The heart
`of the electronics is the pulse Width modulated (“PWM”)
`inverter Which performs bi-directional poWer conversion
`from the DC bus to the preferred three phase variable
`frequency AC required to excite the brushless motor/
`generator in the ?yWheel module. Because the PM brushless
`motor/generator is a synchronous machine, commutation
`sensors are required to determine the angular position of the
`rotor 85 relative to the stator. The unit can be driven With a
`device such as, for example, a Performance Controls
`inverter drive (part number ELM-1000). During charging of
`the ?yWheel, the PWM converter is under charge control
`Which is implemented by regulating the DC bus voltage
`supplied from the UPS system to a constant voltage loWer
`than the operating voltage of the UPS charger until such time
`as the ?yWheel reaches top speed. At this time the controller
`automatically sWitches to a speed control mode, holding the
`?yWheel speed substantially constant at its designed speed,
`e.g., 30,000 RPM. This can be accomplished by steady
`trickle charging. Upon the loss of charging voltage, the
`system automatically sWitches to the discharge control mode
`during Which the output voltage from the PWM inverter is
`held as a constant function of speed independent of the load
`presented. Demand for backup poWer from the ?yWheel can
`be detected in various Ways, for example, by a drop in the
`bus voltage or by a change in the direction of current ?oW.
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`A magnetic bearing control is illustrated in FIG. 9. A
`position sensor, Which measures the axial gap betWeen a
`component that is mounted on the shaft and a ?xed com
`ponent mounted on the ?ywheel housing in a convenient
`location, provides input to a compensator, preferable a
`proportional, integral and derivative compensator. The com
`pensator provides a signal to a current ampli?er, Which
`supplies the current to the coil of the electromagnet of the
`active bearing.
`A diagram for position sensing by the self-diagnosis
`component is illustrated in FIG. 10. Apair of radial position
`sensors are located at right angles (denoted, for example, X
`and y) to each other at both the top and bottom of the shaft.
`The X and y signals are combined and compared to reference
`signals to determine a state of imbalance in the ?yWheel.
`Signals are provided to monitor the balance and to a fault
`detection circuit for shutdoWn if the imbalance exceeds a
`predetermined level.
`Atypical state transition diagram is illustrated in FIG. 11.
`When the system is turned on, a self test mode is initiated.
`If the self test passes, the system goes into a shutdoWn state.
`If the self test fails, the controller transitions to a faulted
`state. If, While in the faulted state, the system is enabled, it
`transitions back to the self test state. When in the shutdoWn
`state, tWo transitions are possible. If a fault is detected, a
`transition is made to the faulted state. If the system is
`enabled and UPS input poWer is on (i.e., trying to charge the
`?ywheel), the system goes to the charge state. In the
`transition to the charge state, integrators are cleared and the
`gate drivers are turned on.
`When in any state, if a fault is detected, the controller
`transitions to the faulted state and the gate drivers are turned
`off.
`When in the charge state, if the ?yWheel speed is greater
`or equal to the maximum speed or if the system is disabled,
`a transition is made to standby state. When in standby state,
`the speed is maintained in its steady-state range. Once the
`system is in standby state, it Will transition to shutdoWn state
`if the system is disabled. It Will transition to the generate
`state, if input poWer is removed. Once the system is in the
`generate state, it Will transition to shutdoWn state When
`?yWheel speed is beloW a preset minimum or When the
`system is disabled.
`The ?yWheel module of the present invention can be used
`in a con?guration With a plurality of ?yWheel modules
`connected in parallel that Will share the load. This con?gu
`ration can be controlled to automatically share the load,
`preferably by using a control technique that does not require
`designating master and slave units.
`During the discharge mode, the DC output current is
`preferably electronically limited to a safe overload value.
`The controller also preferably employs both DC overvoltage
`protection and ?yWheel overspeed protection as Well as
`motor phase overcurrent protection, any of Which Will
`remove the gate drive signals from the inverter output
`transistors. This action enables the ?yWheel to coast to a
`stop. Preferably, a discharge resistor is used to stop the
`?yWheel more quickly.
`The controller is preferably con?gured as a separate unit
`or module so that it can be placed at a location different from
`the ?yWheel module.
`In a typical in-ground installation, the ?yWheel module is
`connected to the system electronics Which are installed, for
`example, in the pedestal along With the users equipment. The
`site typically is prepared by excavating a hole into Which a
`precast, concrete sleeve is placed and back?lled. The sup
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`port tube of the ?yWheel module slides inside the sleeve and
`connection is made to the electronics via an underground
`cable. A steel cover is then bolted and locked to the concrete
`sleeve. The containment preferably should be designed to
`ensure that failure of the ?yWheel or any other rotating
`components Will be completely contained inside the con
`crete sleeve.
`The controller preferably contains three commutation
`sensors Which also function as redundant speed sensors, a
`syn