US20070114795A1 - Flywheel system with synchronous reluctance and permanent magnet generators - Google Patents
Flywheel system with synchronous reluctance and permanent magnet generators Download PDFInfo
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- US20070114795A1 US20070114795A1 US11/624,206 US62420607A US2007114795A1 US 20070114795 A1 US20070114795 A1 US 20070114795A1 US 62420607 A US62420607 A US 62420607A US 2007114795 A1 US2007114795 A1 US 2007114795A1
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- flywheel
- generator
- motor
- power
- electric power
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
- F16C32/00—Bearings not otherwise provided for
- F16C32/04—Bearings not otherwise provided for using magnetic or electric supporting means
- F16C32/0406—Magnetic bearings
- F16C32/044—Active magnetic bearings
- F16C32/0442—Active magnetic bearings with devices affected by abnormal, undesired or non-standard conditions such as shock-load, power outage, start-up or touchdown
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
- F16C32/00—Bearings not otherwise provided for
- F16C32/04—Bearings not otherwise provided for using magnetic or electric supporting means
- F16C32/0406—Magnetic bearings
- F16C32/044—Active magnetic bearings
- F16C32/0444—Details of devices to control the actuation of the electromagnets
- F16C32/0457—Details of the power supply to the electromagnets
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16F—SPRINGS; SHOCK-ABSORBERS; MEANS FOR DAMPING VIBRATION
- F16F15/00—Suppression of vibrations in systems; Means or arrangements for avoiding or reducing out-of-balance forces, e.g. due to motion
- F16F15/30—Flywheels
- F16F15/315—Flywheels characterised by their supporting arrangement, e.g. mountings, cages, securing inertia member to shaft
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02K—DYNAMO-ELECTRIC MACHINES
- H02K7/00—Arrangements for handling mechanical energy structurally associated with dynamo-electric machines, e.g. structural association with mechanical driving motors or auxiliary dynamo-electric machines
- H02K7/02—Additional mass for increasing inertia, e.g. flywheels
- H02K7/025—Additional mass for increasing inertia, e.g. flywheels for power storage
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
- F16C2361/00—Apparatus or articles in engineering in general
- F16C2361/55—Flywheel systems
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
- F16C2380/00—Electrical apparatus
- F16C2380/26—Dynamo-electric machines or combinations therewith, e.g. electro-motors and generators
- F16C2380/28—Motor, generator coupled with a flywheel
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J9/00—Circuit arrangements for emergency or stand-by power supply, e.g. for emergency lighting
- H02J9/04—Circuit arrangements for emergency or stand-by power supply, e.g. for emergency lighting in which the distribution system is disconnected from the normal source and connected to a standby source
- H02J9/06—Circuit arrangements for emergency or stand-by power supply, e.g. for emergency lighting in which the distribution system is disconnected from the normal source and connected to a standby source with automatic change-over, e.g. UPS systems
- H02J9/066—Circuit arrangements for emergency or stand-by power supply, e.g. for emergency lighting in which the distribution system is disconnected from the normal source and connected to a standby source with automatic change-over, e.g. UPS systems characterised by the use of dynamo-electric machines
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02K—DYNAMO-ELECTRIC MACHINES
- H02K7/00—Arrangements for handling mechanical energy structurally associated with dynamo-electric machines, e.g. structural association with mechanical driving motors or auxiliary dynamo-electric machines
- H02K7/08—Structural association with bearings
- H02K7/09—Structural association with bearings with magnetic bearings
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02K—DYNAMO-ELECTRIC MACHINES
- H02K7/00—Arrangements for handling mechanical energy structurally associated with dynamo-electric machines, e.g. structural association with mechanical driving motors or auxiliary dynamo-electric machines
- H02K7/18—Structural association of electric generators with mechanical driving motors, e.g. with turbines
- H02K7/1807—Rotary generators
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/16—Mechanical energy storage, e.g. flywheels or pressurised fluids
Definitions
- the present invention relates to the electromechanical arts and energy storage systems.
- the present invention relates to flywheel systems used for energy storage and conversion.
- Flywheel energy storage systems have provided a mechanical energy storage solution for hundreds of years as evidenced by the potter's wheel. Such systems differ in many respects from modern-day flywheel energy storage solutions. More recent design imperatives including high power density and electric power outputs have led to lightweight, high-speed flywheels operating in evacuated chambers and driving a similarly high-speed electric generator.
- a typical application for today's flywheel is to provide electric power to an electric network for a brief period of time, as might be needed when an electric power outage occurs. Such applications require that the flywheel operate in a stand-by mode, fully charged and ready to convert its mechanical energy into electrical power to support the electrical network when network supply voltage droops.
- the flywheel's internal electrical loads may be deprived of the electric power required to complete a normal flywheel shutdown.
- Critical loads internal to the flywheel system may include electric and electronic controls.
- flywheel system that provides electric power to critical loads during coast down despite the absence of an external power source.
- a flywheel mass supported by electromagnetic bearings is rotatably coupled to a motor-generator for exchanging mechanical power with the motor generator. Further, the flywheel mass is rotatably coupled to a backup generator for converting mechanical energy from the flywheel mass into electrical power for providing electrical power to the electromagnetic bearings.
- FIG. 1 is a diagram showing modules included in the flywheel backup power supply system constructed in accordance with the present invention.
- FIG. 2 is a diagram showing elements included within the power electronics module of the flywheel backup power supply system of FIG. 1 .
- FIG. 3 is a diagram showing elements included in the flywheel module of the flywheel backup power supply system of FIG. 1 .
- FIG. 4 is a diagram showing regimes included in the operation of the flywheel backup power supply system of FIG. 1 .
- FIG. 1 shows the flywheel system 100 of the present invention. It includes the flywheel module 102 , power electronics module 104 , and electrical network 106 .
- a first rotatable coupling 120 interconnects the flywheel mass 112 with the motor-generator 116 and a second rotatable coupling 118 interconnects the flywheel mass with the backup generator 110 .
- At least one electromagnetic bearing 114 provides rotatable support for the flywheel mass.
- the power electronics module 104 is interconnected to sources and consumers of electric power including the backup generator 110 , the motor-generator 116 , and the electrical network 106 , and at least one electromagnetic bearing 114 .
- a first electrical circuit 122 conducts electric power unidirectionally as shown by flow arrow 128 from the backup generator 110 to the power electronics module 104 .
- a second electrical circuit 124 conducts electric power unidirectionally as shown by flow arrow 130 from the power electronics module to at least one electromagnetic bearing 114 .
- a third electrical circuit 126 conducts electric power bi-directionally as shown by the opposed flow arrows 132 , 134 between the motor-generator 116 and the power electronics module.
- a fourth electrical circuit 108 conducts electric power bi-directionally as shown by the opposed flow arrows 136 , 138 between the power electronics module and the electrical network 106 .
- Flywheel system 100 charging includes absorption and storage of mechanical energy by increasing the rotational speed and hence kinetic energy of rotating elements within the flywheel module 102 including the flywheel mass 112 .
- Flywheel system charging takes place when the electrical network 106 supplies electric power as shown by flow arrow 138 and the motor-generator 116 consumes electric power as indicated by flow arrow 132 while functioning as an electric motor.
- Flywheel system 100 discharging includes releasing mechanical energy by decreasing the rotational speed and hence kinetic energy of rotating elements within the flywheel module 102 including flywheel mass 112 .
- Flywheel discharging takes place when the electrical network 106 consumes electrical power as shown by flow arrow 136 that is supplied by the motor-generator 116 as shown by flow arrow 134 while the motor-generator functions as an electric generator.
- FIG. 2 shows a first embodiment of the flywheel system including selected elements of the power electronics module 200 .
- the power electronics module 104 includes three electric power converters.
- the first converter 202 is a uni-directional AC-to-DC converter
- the second converter is a bi-directional AC-to-DC converter 204
- the third converter is a bi-directional DC-to-DC converter 206 .
- the power electronics module also includes an internal DC bus 222 , an external DC bus 108 , and a fifth circuit 224 .
- the first, second, and third circuits interconnect the power electronics module 104 and the flywheel module 102 . What follows is a description of selected sources and users of electric power flowing in these circuits.
- the first circuit 122 interconnects a backup generator AC output 240 as indicated by flow arrow 208 to a first converter AC input 264 .
- the fifth circuit 224 connects a first converter DC output 242 to an external DC bus tap 244 on the external DC bus 108 . Electric power users including the electrical network 106 and the third converter 206 thereby receive backup power from their respective interconnections 246 , 248 with the external DC bus.
- the second circuit 124 interconnects an electromagnetic bearing electric power input 266 to an internal DC bus tap 268 on the internal DC bus 222 .
- Electric power flows from the internal DC bus to the electromagnetic bearing(s) 114 as shown by flow arrow 130 .
- the internal DC bus may receive electric power from the motor-generator 116 , the electric network 106 or the backup generator 110 .
- the motor-generator electrical connection 256 is an AC output interconnected to a second converter AC connection 254 by the third circuit 126 . Power flows from a second converter DC connection 252 as indicated by flow arrow 134 to the internal DC bus.
- an electric network connection 246 is a DC output interconnected to a third converter external DC connection 248 by external DC bus 108 . Power flows from a third converter internal DC connection 250 as indicated by flow arrow 214 to the internal DC bus.
- the backup generator is providing electric power, power flows as described above from the backup generator to the external DC bus and thereafter to the internal DC bus.
- the motor-generator 116 may function either as an electric motor or as an electric generator. During charging the motor-generator functions as an electric motor. During discharging, the motor-generator functions as an electric generator.
- the electric network 106 provides DC power to the third converter 206 via external DC bus 108 as indicated by flow arrow 138 .
- the converter adjusts the voltage to a level suitable for interconnection with the internal DC bus 222 and transfers electric power as indicated by flow arrow 214 to the internal DC bus.
- the second converter 204 takes power from the internal DC bus, synthesizes an AC output indicated by flow arrow 132 , and transfers power to the motor-generator via third circuit 126 .
- the AC output is suitable for powering the motor-generator 116 for accelerating the flywheel 360 (see FIG. 3 ).
- the second converter 204 receives electric power from the motor-generator 116 via third circuit 126 as indicated by flow arrow 134 .
- the converter adjusts the voltage to a level suitable for interconnection with the internal DC bus 222 and transfers electric power to the internal DC bus.
- the third converter 206 takes power from the internal DC bus and adjusts the voltage as required for interconnection with the external DC bus 108 .
- Flow arrows 216 and 136 indicate transfer of electric power from the second converter to the electrical network via the external DC bus.
- the electrical network 106 is interconnected to the external DC bus 108 , a person of ordinary skill in the art will recognize that the electrical network may include electrical sources and loads having electrical characteristics that differ from those of the external DC bus. Auxiliary electric power converters 230 provide for interconnecting such sources and loads to the extent they are present in the network.
- output 242 of first converter 202 may be processed by third converter 206 as shown in FIG. 2
- a fourth unidirectional DC-to-DC electric power converter (not shown) might be used to interconnect first converter output 242 with the electromagnetic bearings 114 .
- the fourth converter adjusts the voltage level at first converter output 242 to accommodate the requirements of the electromagnetic bearings.
- FIG. 3 shows selected flywheel module elements 300 .
- Rotating elements include the flywheel shaft 346 and the flywheel mass 112 .
- Stationery elements include the flywheel housing 358 , first and second electromagnets 306 , 318 , and first and second electric stators 308 , 342 .
- the flywheel 360 includes the flywheel mass 112 and the flywheel shaft 346 .
- the flywheel shaft includes first and second sections 310 , 314 .
- the flywheel shaft shares a common axis of rotation 322 with and is attached to the flywheel mass.
- the flywheel 360 has integrated features including antifriction bearings 354 , 356 and electromagnetic bearings 324 , 328 , a backup AC generator 110 , and a synchronous reluctance AC motor-generator 116 .
- the sections that follow provide details relating to these features.
- Antifriction bearings 354 , 356 provide rotatable support to the flywheel 360 at low flywheel speeds.
- the flywheel utilizes first and second touchdown bearing shafts 302 , 320 mated with respective first and second antifriction bearings 354 , 356 for rotatable support.
- the antifriction bearings support both radial and thrust loads.
- the touchdown bearing shafts extend outwardly from respective opposing ends of the flywheel shaft and share a common axis of rotation 322 with the flywheel shaft 346 .
- the first and second antifriction bearings 354 , 356 are fixed to respective first and second flywheel housing parts 362 , 364 .
- Electromagnetic bearing(s) 114 provide rotatable support to the flywheel 360 at higher flywheel speeds when the flywheel is no longer supported by the antifriction bearings 354 , 356 , but now relies on at least one electromagnetic bearing for support.
- first and second electromagnetic bearings 324 , 328 are shown.
- the first electromagnetic bearing 324 is proximate to the first shaft section 310 and includes an electromagnet 306 attached to the first flywheel housing part 362 and an adjacent ferromagnetic portion 304 that is integral with the flywheel shaft 346 .
- the second electromagnetic bearing 328 is proximate to the second shaft section 314 and includes an electromagnet 318 attached to the second flywheel housing part 364 and an adjacent ferromagnetic portion 316 that is integral with the flywheel shaft 346 .
- Each of the ferromagnetic portions of the shaft 304 , 316 includes a respective plurality of thin ferromagnetic laminates 332 , 336 having electrical insulation interposed between adjacent laminates.
- These laminated ferromagnetic structures increase the effectiveness of the electromagnetic bearings by reducing eddy current losses.
- eddy currents induced in the ferromagnetic portions by the electromagnets result in I 2 R heating losses.
- the thin ferromagnetic laminates reduce the magnetic flux in (results in smaller induced voltage) and the conductivity of (smaller conductive cross-section) each ferromagnetic laminate. The result is a reduction in eddy current losses by a factor of approximately 1/n 2 where n is the number of lamella in a ferromagnetic portion.
- the backup generator 110 is a variable speed permanent magnet AC machine. It includes a first electrical stator 308 adjacent to a flywheel shaft permanent magnet portion 330 .
- the flywheel shaft permanent magnet portion is in the first flywheel shaft section 310 and includes a permanent magnet 348 integral with the flywheel shaft 346 .
- the backup generator Since a permanent magnet generator is self-exciting, the backup generator generates electric power as long as the flywheel 360 is rotating even if no external source of electric power is available. The backup generator therefore provides electric power to the electromagnetic bearings 324 , 328 when operation of the electromagnetic bearing(s) is desirable and when no other electric power source is available to operate the electromagnetic bearing(s). As a person of ordinary skill in the art will recognize, the power produced by the backup generator may be used to power electric loads internal or external to the flywheel system 100 .
- the motor-generator 116 is any inductive AC machine known to ordinary persons of skill in the art such as a wound-rotor or a reluctance type machine.
- the motor-generator includes a second electrical stator 342 and a rotor 344 .
- the motor-generator 116 is a variable speed synchronous reluctance AC machine.
- the motor-generator includes a second electrical stator 342 adjacent to a flywheel shaft reluctor portion 344 .
- the reluctor portion is in the second flywheel shaft section 314 and includes a plurality of ferromagnetic reluctor poles 352 integral with the flywheel shaft 346 .
- the motor-generator 116 While functioning as an electric motor, the motor-generator 116 transfers torque 332 to the flywheel shaft 346 increasing the rotational speed of the flywheel 360 . While functioning as an electric generator, the motor-generator transfers torque from 366 the flywheel shaft reducing the rotational speed of the flywheel.
- the motor-generator Since the motor-generator is not self-exciting, it produces electric power only when induced electric currents magnetize the rotating reluctor poles 352 . An externally excited stator 342 that is magnetically coupled with the reluctor portion induces such currents. Therefore, the motor-generator 116 cannot generate electric power unless there is a source of electric power external to the motor-generator.
- the power electronics 104 may provide the excitation power; however, when the flywheel 360 speed falls below a minimum value, useful generation of electric power by the motor-generator ends.
- FIG. 4 is a graph 400 that illustrates the charging, charged, and discharging cycle of the flywheel system 100 .
- the vertical axis 402 represents rotational speed of the flywheel mass 112 in revolutions per minute (RPM).
- the horizontal axis 404 represents time.
- flywheel system charging begins when the motor-generator 116 functions as a motor, applying an accelerating torque 332 to the flywheel shaft 346 as electrical power is converted to mechanical motion.
- the electromagnetic bearing(s) 324 , 328 operate during speed range S 1 to substantially disengage the touchdown bearing shafts 302 , 320 from the antifriction bearings 354 , 356 ; this is termed “liftoff” 408 .
- the flywheel 360 is accelerated to the maximum speed range S 4 .
- the flywheel Upon reaching speed range S 4 , the flywheel is fully charged 412 .
- the motor-generator cycles on and off as required to maintain flywheel speed within speed range S 4 . This cycling is required to recover speed decay resulting from friction and other losses in the system.
- Electric power supplied to the internal DC bus by the electrical network also powers the electromagnetic bearing(s) 114 via second electrical circuit 124 as indicated by flow arrow 130 .
- the discharging period 426 begins when the motor-generator 116 functions as a generator, applying a retarding torque 366 to the flywheel shaft 346 and converting the energy of mechanical motion into electric power. During this process, the rotational speed of the flywheel 360 is reduced. As the speed decreases from speed range S 4 to speed S 3 , the motor-generator generates electric power. Note that similar flywheel discharging occurs when the electrical network's external power source 232 is interrupted: In this case, the power flow to the electrical network 106 indicated by flow arrow 258 stops and the electrical network becomes dependent on the flywheel system for delivery of electric power via external DC bus 108 as indicated by flow arrow 136 .
- electrical power from the motor-generator 116 is conducted in the direction of flow arrow 134 via the third circuit 126 , the second converter 204 , the internal DC bus 222 , the third converter 206 , and the external DC bus 108 to the electrical network 106 as indicated by flow arrow 136 .
- Electrical power supplied to the internal DC bus by the motor-generator also powers the electromagnetic bearings 324 , 328 via the second circuit 124 as indicated by flow arrow 130 .
- the synchronous reluctance (inductive) motor-generator 116 is no longer able to provide enough electric power to operate the electromagnetic bearing(s) 324 , 328 .
- the backup generator 110 provides sufficient electric power to operate the electromagnetic bearings.
- the backup generator also provides electric power for other electrical loads that may be necessary to the safe shut-down of the flywheel. As one who is skilled in the art will recognize, backup generator power is available via external DC tap 244 and internal DC tap 268 for powering critical loads whether they be internal or external to the flywheel system 100 .
- the backup power speed regime 416 electrical power from the backup generator 110 flows as indicated by flow arrow 208 via the first converter, the fifth circuit 224 , the external DC bus 108 , the third converter 206 , the internal DC bus 222 , and the sixth circuit 124 to the electromagnetic bearings 114 as indicated by the flow arrow 130 .
- the third converter is included in the power flow path to accommodate the backup generator's variable voltage output that rises and falls with the speed of the flywheel 360 .
- Post-touchdown 420 begins when the speed of the flywheel 360 falls below speed range S 2 . This regime is the final portion of the discharging process 426 . If a source of external power is not available, the flywheel will come to rest.
Abstract
Description
- This application is a continuation of U.S. application Ser. No. 11/251,394 filed Oct. 14, 2005, which claims priority from U.S. Divisional application Ser. No. 10/863,868 filed Jun. 7, 2004 now U.S. Pat. No. 7,109,622, which claims priority from U.S. Provisional Application 60/476,226 filed Jun. 6, 2003.
- 1. Field of the Invention
- The present invention relates to the electromechanical arts and energy storage systems. In particular, the present invention relates to flywheel systems used for energy storage and conversion.
- 2. Description of Related Art
- Flywheel energy storage systems have provided a mechanical energy storage solution for hundreds of years as evidenced by the potter's wheel. Such systems differ in many respects from modern-day flywheel energy storage solutions. More recent design imperatives including high power density and electric power outputs have led to lightweight, high-speed flywheels operating in evacuated chambers and driving a similarly high-speed electric generator.
- A typical application for today's flywheel is to provide electric power to an electric network for a brief period of time, as might be needed when an electric power outage occurs. Such applications require that the flywheel operate in a stand-by mode, fully charged and ready to convert its mechanical energy into electrical power to support the electrical network when network supply voltage droops.
- To the extent that a protracted power outage occurs and the flywheel's usable electric output is depleted by the external electric network, the flywheel's internal electrical loads may be deprived of the electric power required to complete a normal flywheel shutdown. Critical loads internal to the flywheel system may include electric and electronic controls.
- Supplying electric loads internal to the flywheel system during coast down presents a particular problem when the flywheel's electric generator has a minimum operating speed as is typical of inductive generators. Here, another source of electric power will be needed during some portion of the coast down period.
- Now, in accordance with the invention, there has been found a flywheel system that provides electric power to critical loads during coast down despite the absence of an external power source. A flywheel mass supported by electromagnetic bearings is rotatably coupled to a motor-generator for exchanging mechanical power with the motor generator. Further, the flywheel mass is rotatably coupled to a backup generator for converting mechanical energy from the flywheel mass into electrical power for providing electrical power to the electromagnetic bearings.
- The present invention is described with reference to the accompanying drawings that illustrate the present invention and, together with the description, explain the principles of the invention enabling a person skilled in the relevant art to make and use the invention.
-
FIG. 1 is a diagram showing modules included in the flywheel backup power supply system constructed in accordance with the present invention. -
FIG. 2 is a diagram showing elements included within the power electronics module of the flywheel backup power supply system ofFIG. 1 . -
FIG. 3 is a diagram showing elements included in the flywheel module of the flywheel backup power supply system ofFIG. 1 . -
FIG. 4 is a diagram showing regimes included in the operation of the flywheel backup power supply system ofFIG. 1 . -
FIG. 1 shows theflywheel system 100 of the present invention. It includes theflywheel module 102,power electronics module 104, andelectrical network 106. In the flywheel module, a firstrotatable coupling 120 interconnects theflywheel mass 112 with the motor-generator 116 and a secondrotatable coupling 118 interconnects the flywheel mass with thebackup generator 110. At least oneelectromagnetic bearing 114 provides rotatable support for the flywheel mass. - The
power electronics module 104 is interconnected to sources and consumers of electric power including thebackup generator 110, the motor-generator 116, and theelectrical network 106, and at least oneelectromagnetic bearing 114. - A first
electrical circuit 122 conducts electric power unidirectionally as shown byflow arrow 128 from thebackup generator 110 to thepower electronics module 104. A secondelectrical circuit 124 conducts electric power unidirectionally as shown byflow arrow 130 from the power electronics module to at least oneelectromagnetic bearing 114. A thirdelectrical circuit 126 conducts electric power bi-directionally as shown by theopposed flow arrows generator 116 and the power electronics module. A fourthelectrical circuit 108 conducts electric power bi-directionally as shown by theopposed flow arrows electrical network 106. -
Flywheel system 100 charging includes absorption and storage of mechanical energy by increasing the rotational speed and hence kinetic energy of rotating elements within theflywheel module 102 including theflywheel mass 112. Flywheel system charging takes place when theelectrical network 106 supplies electric power as shown byflow arrow 138 and the motor-generator 116 consumes electric power as indicated byflow arrow 132 while functioning as an electric motor. -
Flywheel system 100 discharging includes releasing mechanical energy by decreasing the rotational speed and hence kinetic energy of rotating elements within theflywheel module 102 includingflywheel mass 112. Flywheel discharging takes place when theelectrical network 106 consumes electrical power as shown byflow arrow 136 that is supplied by the motor-generator 116 as shown byflow arrow 134 while the motor-generator functions as an electric generator. -
FIG. 2 shows a first embodiment of the flywheel system including selected elements of thepower electronics module 200. Thepower electronics module 104 includes three electric power converters. Thefirst converter 202 is a uni-directional AC-to-DC converter, the second converter is a bi-directional AC-to-DC converter 204, and the third converter is a bi-directional DC-to-DC converter 206. The power electronics module also includes aninternal DC bus 222, anexternal DC bus 108, and afifth circuit 224. - As mentioned above, the first, second, and third circuits interconnect the
power electronics module 104 and theflywheel module 102. What follows is a description of selected sources and users of electric power flowing in these circuits. - The
first circuit 122 interconnects a backupgenerator AC output 240 as indicated byflow arrow 208 to a first converter AC input 264. Thefifth circuit 224 connects a firstconverter DC output 242 to an external DC bus tap 244 on theexternal DC bus 108. Electric power users including theelectrical network 106 and thethird converter 206 thereby receive backup power from theirrespective interconnections - The
second circuit 124 interconnects an electromagnetic bearing electric power input 266 to an internalDC bus tap 268 on theinternal DC bus 222. Electric power flows from the internal DC bus to the electromagnetic bearing(s) 114 as shown byflow arrow 130. The internal DC bus may receive electric power from the motor-generator 116, theelectric network 106 or thebackup generator 110. When the motor-generator is providing electric power, the motor-generatorelectrical connection 256 is an AC output interconnected to a secondconverter AC connection 254 by thethird circuit 126. Power flows from a secondconverter DC connection 252 as indicated byflow arrow 134 to the internal DC bus. When the electric network is providing electric power, anelectric network connection 246 is a DC output interconnected to a third converterexternal DC connection 248 byexternal DC bus 108. Power flows from a third converter internal DC connection 250 as indicated byflow arrow 214 to the internal DC bus. When the backup generator is providing electric power, power flows as described above from the backup generator to the external DC bus and thereafter to the internal DC bus. - Turning now to electric power flows associated with charging and discharging the
flywheel system 100, the motor-generator 116 may function either as an electric motor or as an electric generator. During charging the motor-generator functions as an electric motor. During discharging, the motor-generator functions as an electric generator. - During charging, the
electric network 106 provides DC power to thethird converter 206 viaexternal DC bus 108 as indicated byflow arrow 138. The converter adjusts the voltage to a level suitable for interconnection with theinternal DC bus 222 and transfers electric power as indicated byflow arrow 214 to the internal DC bus. Thesecond converter 204 takes power from the internal DC bus, synthesizes an AC output indicated byflow arrow 132, and transfers power to the motor-generator viathird circuit 126. The AC output is suitable for powering the motor-generator 116 for accelerating the flywheel 360 (seeFIG. 3 ). - During discharging, the
second converter 204 receives electric power from the motor-generator 116 viathird circuit 126 as indicated byflow arrow 134. The converter adjusts the voltage to a level suitable for interconnection with theinternal DC bus 222 and transfers electric power to the internal DC bus. Thethird converter 206 takes power from the internal DC bus and adjusts the voltage as required for interconnection with theexternal DC bus 108.Flow arrows - It should be noted that although the
electrical network 106 is interconnected to theexternal DC bus 108, a person of ordinary skill in the art will recognize that the electrical network may include electrical sources and loads having electrical characteristics that differ from those of the external DC bus. Auxiliaryelectric power converters 230 provide for interconnecting such sources and loads to the extent they are present in the network. - It should also be noted that while
output 242 offirst converter 202 may be processed bythird converter 206 as shown inFIG. 2 , in a second embodiment, a fourth unidirectional DC-to-DC electric power converter (not shown) might be used to interconnectfirst converter output 242 with theelectromagnetic bearings 114. In this embodiment, the fourth converter adjusts the voltage level atfirst converter output 242 to accommodate the requirements of the electromagnetic bearings. -
FIG. 3 shows selectedflywheel module elements 300. Rotating elements include theflywheel shaft 346 and theflywheel mass 112. Stationery elements include theflywheel housing 358, first andsecond electromagnets electric stators flywheel 360 includes theflywheel mass 112 and theflywheel shaft 346. The flywheel shaft includes first andsecond sections rotation 322 with and is attached to the flywheel mass. - The
flywheel 360 has integrated features includingantifriction bearings electromagnetic bearings backup AC generator 110, and a synchronous reluctance AC motor-generator 116. The sections that follow provide details relating to these features. -
Antifriction bearings flywheel 360 at low flywheel speeds. The flywheel utilizes first and secondtouchdown bearing shafts second antifriction bearings rotation 322 with theflywheel shaft 346. The first andsecond antifriction bearings flywheel housing parts - Electromagnetic bearing(s) 114 provide rotatable support to the
flywheel 360 at higher flywheel speeds when the flywheel is no longer supported by theantifriction bearings electromagnetic bearings electromagnetic bearing 324 is proximate to thefirst shaft section 310 and includes anelectromagnet 306 attached to the firstflywheel housing part 362 and an adjacentferromagnetic portion 304 that is integral with theflywheel shaft 346. The secondelectromagnetic bearing 328 is proximate to thesecond shaft section 314 and includes anelectromagnet 318 attached to the secondflywheel housing part 364 and an adjacentferromagnetic portion 316 that is integral with theflywheel shaft 346. - Each of the ferromagnetic portions of the
shaft ferromagnetic laminates - The
backup generator 110 is a variable speed permanent magnet AC machine. It includes a firstelectrical stator 308 adjacent to a flywheel shaftpermanent magnet portion 330. The flywheel shaft permanent magnet portion is in the firstflywheel shaft section 310 and includes apermanent magnet 348 integral with theflywheel shaft 346. - Since a permanent magnet generator is self-exciting, the backup generator generates electric power as long as the
flywheel 360 is rotating even if no external source of electric power is available. The backup generator therefore provides electric power to theelectromagnetic bearings flywheel system 100. - The motor-
generator 116 is any inductive AC machine known to ordinary persons of skill in the art such as a wound-rotor or a reluctance type machine. The motor-generator includes a secondelectrical stator 342 and arotor 344. - In an embodiment, the motor-
generator 116 is a variable speed synchronous reluctance AC machine. Here, the motor-generator includes a secondelectrical stator 342 adjacent to a flywheelshaft reluctor portion 344. The reluctor portion is in the secondflywheel shaft section 314 and includes a plurality offerromagnetic reluctor poles 352 integral with theflywheel shaft 346. - While functioning as an electric motor, the motor-
generator 116transfers torque 332 to theflywheel shaft 346 increasing the rotational speed of theflywheel 360. While functioning as an electric generator, the motor-generator transfers torque from 366 the flywheel shaft reducing the rotational speed of the flywheel. - Since the motor-generator is not self-exciting, it produces electric power only when induced electric currents magnetize the
rotating reluctor poles 352. An externallyexcited stator 342 that is magnetically coupled with the reluctor portion induces such currents. Therefore, the motor-generator 116 cannot generate electric power unless there is a source of electric power external to the motor-generator. Thepower electronics 104 may provide the excitation power; however, when theflywheel 360 speed falls below a minimum value, useful generation of electric power by the motor-generator ends. -
FIG. 4 is agraph 400 that illustrates the charging, charged, and discharging cycle of theflywheel system 100. Thevertical axis 402 represents rotational speed of theflywheel mass 112 in revolutions per minute (RPM). Thehorizontal axis 404 represents time. - Starting from a stand-still and during
pre-liftoff 406, flywheel system charging begins when the motor-generator 116 functions as a motor, applying an acceleratingtorque 332 to theflywheel shaft 346 as electrical power is converted to mechanical motion. As theflywheel 360 speed increases, the electromagnetic bearing(s) 324, 328 operate during speed range S1 to substantially disengage thetouchdown bearing shafts antifriction bearings - During the
post-liftoff period 410, theflywheel 360 is accelerated to the maximum speed range S4. Upon reaching speed range S4, the flywheel is fully charged 412. Prior to discharging, the motor-generator cycles on and off as required to maintain flywheel speed within speed range S4. This cycling is required to recover speed decay resulting from friction and other losses in the system. - While charging 424 and cyclically while charged 412, electrical power from the
electrical network 106 is conducted in the direction offlow arrow 214 viaexternal DC bus 108, thethird converter 206, theinternal DC bus 222, thesecond converter 204, and thethird circuit 126 to the motor-generator 116. Electric power supplied to the internal DC bus by the electrical network also powers the electromagnetic bearing(s) 114 via secondelectrical circuit 124 as indicated byflow arrow 130. - The discharging
period 426 begins when the motor-generator 116 functions as a generator, applying a retardingtorque 366 to theflywheel shaft 346 and converting the energy of mechanical motion into electric power. During this process, the rotational speed of theflywheel 360 is reduced. As the speed decreases from speed range S4 to speed S3, the motor-generator generates electric power. Note that similar flywheel discharging occurs when the electrical network'sexternal power source 232 is interrupted: In this case, the power flow to theelectrical network 106 indicated byflow arrow 258 stops and the electrical network becomes dependent on the flywheel system for delivery of electric power viaexternal DC bus 108 as indicated byflow arrow 136. - During the initial discharging
period 414, electrical power from the motor-generator 116 is conducted in the direction offlow arrow 134 via thethird circuit 126, thesecond converter 204, theinternal DC bus 222, thethird converter 206, and theexternal DC bus 108 to theelectrical network 106 as indicated byflow arrow 136. Electrical power supplied to the internal DC bus by the motor-generator also powers theelectromagnetic bearings second circuit 124 as indicated byflow arrow 130. - When the
flywheel 360 reaches the minimum motor-generator speed S3, the synchronous reluctance (inductive) motor-generator 116 is no longer able to provide enough electric power to operate the electromagnetic bearing(s) 324, 328. During the subsequent backup power speed regime 416, thebackup generator 110 provides sufficient electric power to operate the electromagnetic bearings. The backup generator also provides electric power for other electrical loads that may be necessary to the safe shut-down of the flywheel. As one who is skilled in the art will recognize, backup generator power is available via external DC tap 244 andinternal DC tap 268 for powering critical loads whether they be internal or external to theflywheel system 100. - When
touchdown 418 occurs in speed range S2, the electromagnetic bearing(s) are no longer needed and theantifriction bearing shafts respective antifriction bearings - During the backup power speed regime 416, electrical power from the
backup generator 110 flows as indicated byflow arrow 208 via the first converter, thefifth circuit 224, theexternal DC bus 108, thethird converter 206, theinternal DC bus 222, and thesixth circuit 124 to theelectromagnetic bearings 114 as indicated by theflow arrow 130. Here, the third converter is included in the power flow path to accommodate the backup generator's variable voltage output that rises and falls with the speed of theflywheel 360. -
Post-touchdown 420 begins when the speed of theflywheel 360 falls below speed range S2. This regime is the final portion of the dischargingprocess 426. If a source of external power is not available, the flywheel will come to rest. - While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. It will be understood by those skilled in the art that various changes in form and details can be made therein without departing from the spirit and scope of the invention as defined in the appended claims. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.
Claims (4)
Priority Applications (4)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US11/624,206 US20070114795A1 (en) | 2003-06-06 | 2007-01-17 | Flywheel system with synchronous reluctance and permanent magnet generators |
US12/340,619 US8030787B2 (en) | 2003-06-06 | 2008-12-19 | Mbackup flywheel power supply |
US12/371,453 US7633172B2 (en) | 2003-06-06 | 2009-02-13 | Three plus three phase flywheel power supply |
US12/607,923 US7855465B2 (en) | 2003-06-06 | 2009-10-28 | Three plus three phase flywheel electric power supply |
Applications Claiming Priority (4)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US47622603P | 2003-06-06 | 2003-06-06 | |
US10/863,868 US7109622B2 (en) | 2003-06-06 | 2004-06-07 | Flywheel system with synchronous reluctance and permanent magnet generators |
US11/251,394 US7187087B2 (en) | 2003-06-06 | 2005-10-14 | Flywheel system with synchronous reluctance and permanent magnet generators |
US11/624,206 US20070114795A1 (en) | 2003-06-06 | 2007-01-17 | Flywheel system with synchronous reluctance and permanent magnet generators |
Related Parent Applications (1)
Application Number | Title | Priority Date | Filing Date |
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US11/251,394 Continuation US7187087B2 (en) | 2003-06-06 | 2005-10-14 | Flywheel system with synchronous reluctance and permanent magnet generators |
Related Child Applications (2)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US12/340,619 Continuation-In-Part US8030787B2 (en) | 2003-06-06 | 2008-12-19 | Mbackup flywheel power supply |
US12/371,453 Continuation US7633172B2 (en) | 2003-06-06 | 2009-02-13 | Three plus three phase flywheel power supply |
Publications (1)
Publication Number | Publication Date |
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US20070114795A1 true US20070114795A1 (en) | 2007-05-24 |
Family
ID=33493515
Family Applications (3)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US10/863,868 Active US7109622B2 (en) | 2003-06-06 | 2004-06-07 | Flywheel system with synchronous reluctance and permanent magnet generators |
US11/251,394 Active US7187087B2 (en) | 2003-06-06 | 2005-10-14 | Flywheel system with synchronous reluctance and permanent magnet generators |
US11/624,206 Abandoned US20070114795A1 (en) | 2003-06-06 | 2007-01-17 | Flywheel system with synchronous reluctance and permanent magnet generators |
Family Applications Before (2)
Application Number | Title | Priority Date | Filing Date |
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US10/863,868 Active US7109622B2 (en) | 2003-06-06 | 2004-06-07 | Flywheel system with synchronous reluctance and permanent magnet generators |
US11/251,394 Active US7187087B2 (en) | 2003-06-06 | 2005-10-14 | Flywheel system with synchronous reluctance and permanent magnet generators |
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US (3) | US7109622B2 (en) |
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Also Published As
Publication number | Publication date |
---|---|
US20060038453A1 (en) | 2006-02-23 |
US7187087B2 (en) | 2007-03-06 |
US7109622B2 (en) | 2006-09-19 |
US20040245877A1 (en) | 2004-12-09 |
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