final report boeing cooperative agreement no. de-fc36-02go12112 6-30-07

8/14/2019 Final Report Boeing Cooperative Agreement No. de-FC36-02GO12112 6-30-07

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Final report Cooperative Agreement No. DE-FC36-02GO12112

The views and conclusions contained in this document are those of the authorsand should not be interpreted as necessarily representing the official policies orendorsements, either expressed or implied, of the Department of Energy or theU. S. Government.

SUPERCONDUCTING FLYWHEEL POWER RISK MANAGEMENT SYSTEMCOMMERCIAL ENTRY PHASE

Final Report for the Period November 1, 2002 March 31, 2007

Submitted by: Boeing Phantom Works

Program Manager:Dr. Michael Strasik

206-544-5389

Principal Investigator:2002 2006 Art Day, Phil Johnson

2006 2007 Dr. John Hull206-544-5803

Team Members:

Boeing Phantom WorksSouthern California EdisonPraxair Specialty Ceramics CorporationPraxair CryogenicsBallard Power SystemsAshman TechnologiesArgonne National Laboratory

PREPARED FOR THE UNITED STATESDEPARTMENT OF ENERGYUnder Cooperative Agreement

No. DE-FC36-02GO12112

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A preliminary system design was going to be developed in Task 3,concluding with a team-wide preliminary design review. At this point we weregoing to authorize risk-reduction experiments for those parts of the systemthat still appear to pose significant obstacles. For example, finite-elementmodeling of the spoke system has revealed this component to be one of the

greatest obstacles to successful flywheel design. Other candidates for riskreduction include large rotor winding, HTS bearing losses, and cryostatsealing techniques. Subsequent tasks would build and test these componentsto ensure reliable final designs.

Throughout the first year of the program the team would conductoptimization studies of the HTS bearing approach, using subscale tests aswell as electromagnetic modeling in an effort to better understand and reducesystem losses. ANL was assisting with complementary studies. Boeing andPraxair were planning to also work to enhance HTS material properties,particularly Jc. The bearing and HTS materials efforts comprised Tasks 4 and5.

While this program cannot answer all questions on subsystem reliability,Task 6 was supposed to begin the process of accumulating long-term data oncycling and operation of appropriate sub-scale components. These were toinclude rotors and also subscale HTS subsystems. Task 7 was to addressrotor material properties systematically from the coupon level up throughcomplete rotors. Task 8 was to address the proposed sub-slab installation ofthe flywheel system with the assistance of qualified civil engineers.

Finally, an ongoing System Engineering task was to coordinate this and allother work to keep it relevant to the defined System Requirements. This wasplanned to be done, in part, by systematically updating a series of systemperformance budgets in spreadsheet format. The rotordynamics consultingfirm Vibragon was employed to augment Boeings modeling of systemdynamic performance.

This project was initially partially funded at a very small level and the mainfocus was on the first three tasks of the proposed project. The BoeingCompany changed cost policy determination of the original proposal resultingin doubling of the proposed labor rates on the project. As a result of thatfinancial reclassification from the original proposal, it was mutually agreed byBoeing and DOE to put the project on hold until a successful renegotiationwould take place with the new rates. Therefore, the project was put on hold inMarch 2003, less than a year after start of the contract, and this holdcontinued until it was restarted in August 2006. Only very minimal work wascompleted from August 2006 until the completion of the contract on March 312007, as only about $60K of funding was remaining when the project wasrestarted in 2006. The project was never fully renegotiated between Boeingand DOE, and therefore the original objective of the proposal was neverachieved, and only limited amount of accomplishments on the first three taskswas completed. This report will summarize those accomplishments.

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The original Phase III effort was proposed while the Boeing team was inthe initial stages of Phase II development, prior to testing of the large 10-kWhflywheel system. That design included an innovative but unproven compositespoke system, chosen to give the flywheel a high energy density.Unfortunately, it encountered a dynamic response during full integration

testing that resulted in damage to the flywheel system. As a result of this testexperience, the Boeing team used more conservative design approach whendesigning the 5-kWh / 100-kW UPS for utility testing. A key element of thisconservative approach was proven by a successful full-speed spin test of theredesigned metal hub and a composite rotor.

To build on this experience base, we are now proposing a stagedapproach in the development of the worlds largest composite flywheelsystem with superconducting bearings. As part of our existing Phase IIflywheel project, we will design, build, and test a 10-kWh hub/rotor systembased on our successful approach with the 5-kWh design. In a new Phase IIB

program, we are proposing to develop preliminary design for a 30-kWh / 100-kW flywheel power risk management system. As part of the preliminarydesign effort, we will also conduct a detailed design on the critical full-sizedhub/rotor system. Boeing will lead the team in design and fabrication to verifythe design and modeling approach, before continuing with a detailed designof the complete system. Given the development status of this technology, theBoeing team feels that the most will be gained by focusing on the high-riskaspects, with ambitious goals for both basic technology development andscale-up of new technology, rather than on final product development anddemonstration. The proposed cost matching ratio reflects these developmentrisks.

In the following section, a brief review of the market assessment and anestablished need for the flywheel based Power Risk Management System issummarized.

2. NEED FOR POWER RISK MANAGEMENT

The power market has changed dramatically in the last several years andwill continue to evolve -- with both users and providers looking for smarterstrategies and technologies. Risk management will be much more

individualized, and a significant number of power users will need localizedsolutions under their own control. With the advent of rolling blackouts on boththe West and East Coasts of the United States, reliability of power hasbecome even more critical. Meanwhile, peak prices are rising dramatically.Inevitably, the greatest costs will be borne by those drawing during peakhours, and unlike existing uninterruptible power supply (UPS) systems,flywheels have the potential to store significant amounts of energy at areasonable cost.

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It was the aim of this program to develop the first flywheel electricitysystems that give power users and utilities a full-scale device to manage boththeir cost and reliability risks. This development relies fundamentally onadvances in the capabilities of high-temperature superconducting (HTS)

materials. Principal reasons include the need for a system that can be cycledtens of thousands of times, is easy to control and therefore reliable, has nowear parts in critical mechanisms, and is far more efficient than flywheels withnon-HTS suspensions. Figure 1 shows the design for Boeings 5-kWhflywheel system being developed under the Phase-2 cooperative agreementbetween the Boeing team and DOE, which was the point of departure for thisnew program.

Figure 1. Boeing 5- kWh Flywheel.

2.1. Background of Application

2.1.1. PROPOSED HTS SYSTEM

The HTS system we proposed was conceived as a result of newconditions in power markets and the emerging needs of power consumers.Both utilities and business operators are increasingly looking for innovativeways to manage the risks of grid-provided power.

The system we proposed to fill this need is a superconducting flywheelpower Risk Management System (RMS). The system, shown schematically in

figure 2, will (1) provide uninterruptible power with significant ride-throughcapabilities, (2) efficiently store off-peak energy and then autonomously re-supply that energy when peak power rates are in effect, and (3) condition gridpower to maintain near-unity power factors at the meter and at critical loads.

We sized this system for an output of 100-kW average power and a totalstored energy of 30-kWh. This size was recommended by our team memberSCE based on the needs of their small and medium-sized commercialcustomers, and SCEs own plans to develop distributed power resources.

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They are very interested in avoiding the costs and delays associated withsiting new transmission lines to accommodate the growing loads in urbanareas.

POWER INVERTER

AND CONDITIONER

FLYWHEEL MOTOR

CONTROLLER

POWER TO

CUSTOMER

CUSTOMER

UTILITY

VAULT

POWER FROM

UTILITY GRID

$

FLYWHEEL

STORAGE UNIT

POWER INVERTER

AND CONDITIONER

FLYWHEEL MOTOR

CONTROLLER

POWER TO

CUSTOMER

CUSTOMER

UTILITY

VAULT

POWER FROM

UTILITY GRID

$

FLYWHEEL

STORAGE UNIT

Figure 2. Schematic Operational Diagram of Boeing Flywheel Power RiskManagement System.

Previous and ongoing flywheel work at Boeing and elsewhere has focused

on the potential use of flywheels to act as uninterruptible power systems(UPS). This potential is growing, with the recent introductions of smallflywheels for immediate backup until on-site diesel generators come online.The Boeing product concept includes this function, but also addresses theemerging susceptibility of electricity to prolonged outages and exceedinglyhigh peak-demand price. Members of our User Advisory Group (SCE,Clearwood Electric, Alaska Energy Authority, GE Power Systems, and BoeingFacilities) have expressed a strong interest in flywheels to protect them fromthe economic risk of these high peak prices. Finally, many customers nowrequire harmonic filtering and power factor correction. Rather than forcecustomers to solve all of these problems individually, the flywheel RMS will

use the enabling efficiency and storage capacity of flywheels withsuperconducting bearings to meet the need for comprehensive power riskmanagement.

The Boeing system as initially introduced would consist of three units: (1)a power inverter and conditioning unit that also houses the flywheels motorcontroller, (2) the flywheel storage unit in a vacuum canister with integralcryocooler, and (3) a customer utility vault for the flywheel storage unit.

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Eventually, fully qualified containers may become integral parts of the storageunits but early customers will prefer the assurance of below groundinstallation.

In operation, the ac power unit will receive power from the utility grid andtransfer some part of this power to the flywheel storage unit through a

motor/generator and motor controller. Because the flywheel unit can store asignificant amount of energy (typically sized for 1 to 3 hours usage), it willprimarily draw power when grid demand and prices are low. When prices arehigh, or when power is interrupted, the unit will deliver this power to thecustomer at low cost. At all times, the integrated inverter/controller unit willmaintain good power quality and correct the power factor to the benefit of theutility as well as the customer. The system itself will run continuously, with arated lifetime in excess of 20 years. Potential commercial uses of the RiskManagement System are numerous because power cost and reliability arecentral to the operation of our economy.

2.1.2. ADVANTAGES OVER COMPETING TECHNOLOGIES

Competing storage technologies include batteries, coil-basedsuperconducting magnetic energy storage (SMES), pumped hydro,compressed air, and non-HTS flywheels. The flywheel RMS was also becompared with centralized gas turbines and distributed microturbines.

Conventional UPS devices have evolved out of a combination of dieselengines, generators, batteries, and UPS electronics. Chemical-basedbatteries, which provide temporary power for nearly all UPS systems, have

numerous problems. Probably the most significant of these is the fact thatbatteries will weaken substantially over the operating life of a system. Thisreduces the reliability of the uninterruptible component and requires ongoingtesting, maintenance, and finally disposal and replacement of the batterystring. At Boeings Bellevue Data Center, batteries are replaced every 4 to 6years. The high life-cycle costs of these systems in actual use at Boeing areshown in figure 3. Continued system maintenance is required to ensureadequate battery fluid levels and contact resistances, system health, andhydrogen gas removal. Life cycle battery costs for UPS systems are about$5000 per kWh. Therefore, a flywheel UPS system with a design life of 25years will show an early return on investment, even if initial capital costs are

somewhat higher. The Boeing flywheel energy storage system represents amore reliable, lower-maintenance, environmentally friendly alternative tobatteries for uninterruptible power systems.

SMES systems use the energy stored in the magnetic field generated by acurrent in a superconducting coil. The SMES option might be used to provideshort bursts of power, but cannot compete with flywheels for ride-throughprotection. Foreseeable SMES systems also have very large capital and

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operating costs associated with liquid helium usage. HTS versions seem farin the future.

$-

$2,000,000

$4,000,000

$6,000,000

$8,000,000

$10,000,000

1 3 5 7 9 11 13 15 17 19

Years of System Operation

LifeCycleCost

750 kWh UPS Syste m

Boeing Bellevue Data Center

- 5 year life/battery

- $1.60/Wh battery cost

- includes O&M

- 56,000 lbs

Lead-Acid Batteries

- 25 year lifetime

- $3/Wh FES cost- includes O&M

- 40,000 lbs

750 kWh UPS System20x 35 kWh Flywheels

Figure 3. Boeing Life-Cycle Cost Experience with Battery-Based UPS.

Pumped hydro storage has fairly low efficiency and is geographicallyrestricted to a few (usually large) applications. Compressed air energystorage is another option limited by geography. Neither of these technologiesis easily scalable from its baseline configuration and none offers rapid andefficient response nor distributed storage near points-of-use.

Gas turbines and microturbines are often used as points of reference forstorage system costs. While large gas turbines produce much of the originalpower, they cannot directly help the thousands of commercial customers whoface poor power supply from the grid. Microturbines are being proposed andtested as a way of providing distributed local generation, which would bepreferred by both customers and the utilities. SCE has several such unitsunder test but has found them to be highly inefficient (typically 24%).Downfalls of the microturbines include noise, generation of emissions, andmonthly maintenance. Gas turbines are not solving the customers needs forclean, uninterruptible power.

Emerging competition exists from other flywheel developers, such asBeacon Power, AFS Trinity Power, Active Power, and Pentadyne. Thesecompetitors rely on much less reliable and lossier bearing systems such asmechanical or active electromagnetic, which will result in higher operating and

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replacement costs for customers than the proven Boeing HTS bearing design.Only Active and Pentadyne have truly entered the market so far, with ActivePower having a usable but inefficient and very limited product. Figure 4compares the energy losses for mechanical, electromagnetic, and BoeingHTS bearing. The total bearing loss in the 10 kWh system tested in the Phase

II project met the DOEs goal of HTS bearing loss of 0.1% per hour. Thefigure shows that the HTS bearing is the only economical solution to long-term storage and UPS service. Other factors supporting this conclusioninclude wear of mechanical bearings and complex inductive couplinglimitations of electromagnetic bearings.

0

20

40

60

80

100

0 50 100 150 200Time (Hours)

EnergyRema

ining(%)

Boeing Flywheel

superconducting bearings

(includes cryogenics)

Flywheel

mechanical

bearings

Flywheel

electromagnetic

bearings

Battery

0

20

40

60

80

100

0 50 100 150 200Time (Hours)

EnergyRema

ining(%)

Boeing Flywheel

superconducting bearings

(includes cryogenics)

Flywheel

mechanical

bearings

Flywheel

electromagnetic

bearings

Battery

Figure 4. Energy Remaining in Flywheel with Time for Various Bearing Systems.

Boeings low-loss superconducting bearing is the key technical advantageand leads to several economic benefits. First, the Boeing HTS bearingenables autonomous operation of the flywheel as a peak energy cost/risk-mitigation device; storing power when costs are low and providing that powerback to the user during peak power cost times. Second, the HTS bearing isthe solid-state equivalent of a complex electromagnetic bearing. Thistechnical advantage manifests itself in scalability of design to various sizeswithout the complication of ever increasing inductive coupling and controlproblems. A number of other advantages and benefits to power users arelisted in figure 5.

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Key Feature of Boeing FlywheelPower Risk Management System

Benefits to Electric Power Users

Low loss superconducting bearing Provides energy for peak demand periods (load leveling/following) Peak power price protection Eliminates or minimizes system blackouts and brownouts Smoother, more reliable black start operations Defer investment in new generation capacity Enables better use of wind, solar, or geothermal power sources

Non-contact bearings, simple design Low maintenace compared to batteries, or flywheels with conventional bearings System price target competitive with conventional generation or storage

technologiesFast response time, voltage or currentregulation

Uninterruptible power source Eliminates sags or surges Enhanced power quality Reactive power supply Power oscillation damping

Environmentally benign Green power Allows generation at environmentally acceptable areas No hazardous waste No noise or air pollution

Figure 5. Technical and Economic Benefits of Flywheel Power RiskManagement System.

3. DESCRIPTION OF THE PROPOSED HTS SYSTEM TO BE DEVELOPED

The proposed system approach for the Superconducting Power RiskManagement System takes as its point of departure the work and designsdeveloped under an ongoing Phase II SPI program, also led by Boeing. Inthat program, the ultimate goal is the demonstration of a UPS flywheelproviding 100-kW of power for 30-60 seconds. The demonstration systemwas preceded by a 10-kWh laboratory prototype with a 3-kW average /10-kW

peak power motor, nominally for load leveling. With this system, we havesuccessfully verified many technologies. We have proven stable levitationwith permanent magnet lift system, proven stability and very low loss of oursuperconducting bearing design, built and demonstrated motor/generator withlow negative-stiffness, and successfully operated this motor with novel controlsystem. The motor/generator system was also used to fully control theflywheel system. Full flywheel system stability and operation wasdemonstrated. Unfortunately, this system was later damaged during high-speed testing, where the composite-spoke approach proved to bedynamically difficult. Figure 6 illustrates the 10-kWh flywheel being assembledfor testing and Figure 7 shows subsequent damage after a touch-down event

due to excessive composite spoke flexibility. As a result of this testexperience, the Boeing team used more conservative design approach whendesigning the 5-kWh / 100-kW hub and rotor system. This conservativeapproach was proven by a successful full speed test of the redesigned metalhub and a composite rotor. Figure 8 shows the redesigned composite rotormounted on an aluminum hub being installed for spin testing. Figure 9 showsthe spin testing data showing a successful full speed test (22,900 rpm,

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exceeding the peak operational speed of 22,500 rpm) of the redesigned 5-kWh rotor/metal hub assembly.

The initial design concept for the 30-kWh flywheel unit, carried forwardfrom the 5-kWh / 100-kW prototype, is shown in figure 10, with some

features highlighted.

Composite Rotor. A flywheel rim must withstand tremendous centripetalforces to achieve the most cost-effective use of its carbon-fiber compositematerials. The hub has a similar challenge and must be able to match theradial growth of the wheel. The program will design these components with

Figure 8. 5- kWh Flywheel with anAluminum Hub Being Installed in

Boeing Spin Pit.

Figure 7. 10-kWh Flywheel withComposite Spokes Damaged Durin

SpinTesting.

Figure 6. 10- kWh Flywheel withComposite Spokes Being Installed.

Figure 9. Spin Test Result of 5-kWhFlywheel with an Aluminum Hub.

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realistic factors of safety (typically two or more) and fatigue de-rating factorsto replicate the conditions of a commercial life.

Hybrid HTS/Permanent-Magnet Bearing. The energy losses associatedwith mechanical and electromechanical bearings are prohibitively high for nearlyall potential flywheel applications. These losses are typically at least 3% to 10%

of the stored energy per hour. With hybrid superconducting bearings, we havedemonstrated that it is now possible to obtain losses that are as low as 0.1% perhour - after imposing a cryogenic overhead factor FCOH of 20 30 at 77K. HTSbearings possess other significant advantages such as dynamic stability,simplicity, and reliability. The Boeing-patented bearing design (figure 11)employs horizontally-polarized magnets to achieve a high magnetic stiffnessper unit area of superconductor.

Figure 10. RMS Unit Design, exclusive of Power Electronics and Cryocooler.

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The bearings rely on YBCO materials technology developed at Boeingover the past sixteen years, using a patented process. Boeing produces thelargest and best-quality single-grain YBCO monoliths available in the U.S.(Fig. 11). With critical current densities Jc of about 30,000 A/cm

2 at 77K, thesuperconductors produce interaction forces (with the permanent magnets in

the rotating portion of the bearing) that are sufficiently high to enable a verylow-loss flywheel bearing.

HTS BearingStator

Boeing YBCOCrystal

HTS BearingRotor

Installed HTSBearing

HTS BearingStator

Boeing YBCOCrystal

HTS BearingRotor

Installed HTSBearing

Figure 11. Boeing HTS Stability Bearing.

Lift Magnet System. The system design uses permanent magnet rings tocarry most of the flywheels weight, significantly reducing the thrustrequirement on the HTS bearing. A small but inevitable amount of instability inthe lift system is counteracted with the HTS bearing. This approach has beenvalidated in systems built at Boeing and Argonne.

Cryogenic System. Compared with most potential HTS applications, theFlywheel Risk Management System imposes relatively light requirements onthe cooling load and base temperature. Pulse-tube cooler technology nowpromises to provide the most efficient, reliable cooling for this application.

Pulse-tube cooler designs eliminate moving parts from the cooler and doaway with sliding seals.

Motor/Generator (M/G). The flywheel transforms electrical energy tomechanical and back again through a brushless permanent-magnet motor.An unusual design requirement is that the motor magnets and laminationsmust not destabilize the HTS bearing and flywheel. Team member AshmanTechnologies met this requirement in both 10-kW and 100-kW designs.

Motor Control and Power Conversion Electronics. A motor controllerunit transforms the variable speed motor output to an intermediate dc buslevel. Special algorithms have been developed through Ashman for efficient,sensorless control of the flywheel M/G. From there, the power electronics for

the proposed system will be based very closely on commercial systems nowin use for battery UPS and renewable generation systems, typicallyincorporating power factor correction. These systems are already very simpleto operate and have been developed with standby power requirements as lowas 50W.

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4. INITIAL DESIGN OF THE 38 KWH ROTOR

The first task in the original Phase 3 proposal was to transfer the 100 kWUPS flywheel system, once testing was completed during Phase 2, to SCEand carry out on-site testing. The system must then be capable of unattended

operation and will require a few upgrades to enhance stability and self-monitoring. This task was never completed due to lack of funding in Phase 3and the delay in completing Phase 2 tests, due to redesign of the rotor/hubinterface after previous instabilities described in the previous section.

The thermosyphon cooling loop originally designed by MesoscopicDevices for Phase 2 showed occasional instabilities that led to warming of thesuperconductors above normal limits. This situation could usually bemanaged with personnel on hand, but would not be tolerable for unattendeduse. As a useful task that could be accomplished with the limited fundingcommitted so far for Phase 3, we decided to redesign the thermosyphon

system for more stable operation. This has been done collaboratively withPraxair.

5. SPIN ANALYSIS OF THE 38 KWH FESS

Results of the preliminary rotor spin loads analysis of the 38 kWh systemare presented in the sections below. As a precursor to the analysis of a full-up system, which includes a central hub, the composite rotor without a hubwas subjected to assembly and spin loading. The results show that thisloading will produce acceptable stresses and displacements.

5.1. Model Description.

The rotor design variables are presented in Table 1. The candidate rotorconsists of three hoop wound composite rims. The rim materials as well asthe model attributes are presented in figure 12.

TABLE 1. THE 38 KWH DESIGNVARIABLES

Operating Speed = 20k RPMStored Energy = 38.8 kWhRotor Mass = 686 lb

Rotor Height = 22.5 in

The middle and outer rims have a 0.025 diameter interference fit. As withpreviously performed flywheel analyses, the analysis includes load steps tofollow the assembly sequence. Contact surfaces are used to model theinteraction of bodies with each another. The composite rims are modeled withorthotropic material properties.

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31 ID40 OD0.025 Interference @

T700s/T800s InterfaceContact surfaces

between each rim Central Hub is not

included

Model Attributes

T800S

T700S

S2-Glass

15.5 IR

20.0 IR

Step Description

1 T700s/T800s Press Fit

2 Spi n to 20k RPM

Load Steps

Figure 12. The 38 kWh Axisymmetric Spin Analysis. The FE model was createdwith IDEAS and solved with ABAQUS.

5.2. Results

The results of the spin loads show that the rotor will experienceacceptable stress levels. The absence of a hub should be noted. The shearstress levels will increase once this hardware is included. With that in mind,the resulting max stress levels are presented in table 2. The table shows a

minimum Safety Factor of 1.6 on the hoop stress levels in the inner (S2-Glass) and outer (T800s) rims.

Table 2. The 38 kWh Safety Factors @ 20k RPM

Item MaterialStress

Comp

Stress

(ksi)Fty or Fcy

Safety

FactorRim 1 S2-Glass Radial -5 -40 8.0

Hoop 110 175 1.6Shear 1 7 7.0

Rim 2 T700s Radial -3 -40 13.3

Hoop 233 385 1.7Shear 1 13 13.0Rim 3 T800s Radial -2.5 -40 16.0

Hoop 290 453 1.6Shear 1 7 7.0

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The hoop and radial stress distributions through the rotor thickness arepresented in figure 13. The discontinuities in the curve show the borders ofeach rim.

T800S

T700S

S2-Glass

15.5 IR

20.0 IR

Path-1

290 ksi

233 ksi

110 ksi

Figure 13. The Rotor Radial & Hoop Stress vs. Rotor Thickness at 20K RPM.

The resulting radial displacements of the inner and outer radii, as a

function of load step time, are presented in figure 14. The plot shows that thepress fit causes the IR to contract 0.007r while the rotor OR expands 0.007r.Application of the 20 kRPM spin loads causes the IR of the S2-Glass toexpand to 0.180r inches while the OR expands to 0.175r inches. It should benoted that the linear slope of the response curves, be it displacement, stress,or contact pressure, are due to the fact that the load step time is proportionalto 2, not .

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Press-Fit Spin to 20k RPM

S2-Glass IRT800s OR

Figure 14. The Radial Displacement of the Rotor IR & OR.

6. INITIAL DYNAMIC ANALYSIS OF 38 KWH FLYWHEEL CONCEPT

The XLRotor code was used to extrapolate from the 5 kWh design, basedon the rim concept discussed in the previous section (figure 15). Also, simplescaling was used for the motor/generator to account for the new speed rangeof nominally 10,000 20,000 rpm plus a modest increase in power output, to150 kW. To get the power at the bottom of this speed range, the motorsmagnet area must be increased by roughly a factor of 2.7 from the earlierdesign. This was done by increasing the length by a factor of 1.5 and thediameter by a factor of 1.8.

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31 ID40 OD

0.025 Interference @T700s/T800s InterfaceContact surfaces

between each rim Central Hub is not

included

Model Attributes

T800S

T700S

S2-Glass

15.5 IR

20.0 IR

Step Description

1 T700s/T800s Press Fit

2 Spi n to 20k RPM

Load Steps

Figure 15. The 38 kWh rim design.

The geometry of the scaled design is shown in figure 16. Note the thin rimdesign. If the aluminum hub is to be used, the rim will have to get somewhatthicker (smaller ID) which will increase weight. This will be one of many tradesin developing the working design.

3028

262422

20

1816141210

8

6

42

-25

-15

-5

5

15

25

-5 15 35 55

Axial Location, in

ShaftRadius,

in

FLYWHEEL DYNAMIC MODEL

Figure 16. XLRotor model geometry.

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The computed results for this model show a fairly stiff rotor (a benefit),with a low speed bearing fundamental. However, there is a mode (shown asthe red line in figure 17) that closely follows the speed of the rotor. This wouldlead to excessive vibration at most speeds of less than 5,000 rpm. It may bepossible to hold the rotor on auxiliary bearings through this speed range, but

a better strategy would be to reduce the moment ratio to some numbersignificantly less than 1.0. The key problem at present is that the transverseand polar moments of inertia are nearly equal. Moving the hub lower on therim would also help, as was done on the 5 kWh design. The analysisdescribed here will show the need for fundamental adjustments prior toestablishing component requirements for designers.

Rotordynamic Damped Natural Frequency Map

0

20

40

60

80

100

120

140

160

180

200

0 5000 10000 15000 20000 25000

Rotor Speed, rpm

NaturalFrequency,

H

FLYWHEEL DYNAMIC MODEL

Figure 17. Critical speed map of the initial 38 kWh flywheel design.

7. FACILITY ANALYSIS FOR HIGH-ENERGY TESTING

Boeing has completed an analysis of the High Energy Spin Pit todetermine the best location for both near-term and far-term test activities.Several alternatives were evaluated including relocating the Air Turbinesystem to an adjoining below grade bunker like chamber (FEL Chamber infigure 18) as well as utilizing outside spin test services. Following an initialreview of analysis performed by Lab Operations Test Engineering group, it

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has been determined that the existing pit with the addition of the cementbarrier was the best solution and the analysis indicates that the existing pit issufficient to contain any potential failure and leave the second system intact.The analysishas shown that the two tiers of cement ceiling blocks will not belifted clear of the nested interlock holding the blocks in place. With two layers

of blocks the energy rating is over 60 kWh. It should be noted that thisassumes that the momentum transfer takes place over a 10 ms period. Therating decreases if the duration is shorter, as is shown in figure 19.

Figure 18. Overview of spin test facility configuration.

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21

Momentum Duration (Sec) 0.001 0.005 0.01 0.02

Effective Energy Ratio Ee/Et 75% 75% 75% 75% OD (in) 22.75Load Factor fl 2.00 2.00 2.00 2.00 ID (in) 13.50

H (in) 13.50Energy Density

ED

(KWh/#) Gama (#/in^3) 0.0530

0.01 1.50 7.51 15.01 30.02 RPM 24,000

0.02 2.12 10.61 21.23 42.46 W (lb) 188.43

0.022 2.23 11.13 22.27 44.53 I (#-Ft-Sec^2) 3.55

0.04 3.00 15.01 30.02 60.05 E (KWh) 4.23

0.06 3.68 18.39 36.77 73.54

0.1 4.75 23.74 47.47 94.940.15 5.81 29.07 58.14 ED (KWh/#) 0.022

Energy Density

ED

(KWh/#)

0.01 4.50 22.52 45.03 90.07 H (Ft) 30.02 6.37 31.84 63.69 d (Ft) 3

0.022 6.68 33.40 66.80 b (Ft) 1.8

0.04 9.01 45.03 90.07 L (Ft) 12.5

0.06 11.03 55.16 h (Ft) 20.1 14.24 71.21 p-concrete (lb/Ft3) 144

0.15 17.44 87.21 Ee/Et 75%

#DIV/0! #DIV/0! #DIV/0! #DIV/0! Block Weight (lb) 6,480# 1st Layer Blocks 6.00 Actual Number Hit

# 2nd Layer Blocks 7 Actual Number Hit

Target Energy (KWh) 4.23 W-blocks-total (lb) 84,240MS - 1 Block 4.02

MS - Both Rows of Blocks (3

total) 14.79

Permissible Energy (KWh)

1st & 2nd Layer of Blocks

Energy Density Calculator

Permissible Energy (KWh)

1st Layer of Bolocks Only

Number of Blocks & Block Wieght Calculator

This spreadsheet computs the energy necessary to lift one block due to the change in

direction of the momentum flow.

Figure 19. Boeing 15-08 building block lift Pit rating summary Note that rating isbased on energy concentrated on only one 1st level block, the actual number of

1stand 2nd level blocks calculated in yellow for comparison.

A Test Procedure review was conducted with the analysis presented tothe flywheel group and additional failure possibilities have initiated sometesting and further investigation into likely failure modes. In particular, largepiece projectile failure at these energies shows that the pit walls could bepenetrated beyond the acceptable 4 limit (shown in figure 20, with thin-walledcontainment assumed). Coupon testing in a gas gun as well as a meetingwith Toray Composites America test staff are planned to determine if someabsorbing barrier may be required to line the pit walls.


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Figure 20. Spin Pit wall rating.

8. ACCOMPLISHMENTS ON MOTOR/GENERATOR AND FLYWHEELCONTROLLER SYSTEMS AFTER 3 YEAR PAUSE IN FUNDING

This project was on hold for over 3 years and was restarted in July 2006.The primary objective in this task was to troubleshoot the currentmotor/controller and system controller hardware and software to determineoptimum configuration for a commercial system that would be required for thePower Risk Management System that would be deployed remotely in serviceat a utility customer. This section summarizes our accomplishments andconclusions.

We transitioned motor controller software development and maintenanceto Boeing from the subcontractor, Ohio State University. This software isbeing modified to work with a redesigned commercial motor/controller thatwould be used in a commercial flywheel power risk management system. Wedetermined that real time operational status variables need to be displayed

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and recorded during operation. Initial implementation was completed withrotor torque angle and speed estimations in both Hall-effect mode andsensor-less mode, via CAN bus. Boeing wrote a statement of work for a newmotor/controller and utility interface hardware and solicited proposals fromseveral vendors for an integrated commercially produced motor/controller

system. Anderson Electric Controls, Inc., of Kent, Washington was selectedas the best potential vendor to design and build a future commercial controllersystem that would be compatible with our motor/generator design.

9. STATEMENT OF WORK (SOW) FOR THE MOTOR CONTROLLER FORTHE 25KW FLYWHEEL

This SOW will address the design, build, delivery, and integration of the MotorController for the Boeing Companys 25 kW Flywheel Energy Storage System.

These activities will include:

1. Engineering services to design, build, deliver, and integrate a 25 kW motor /generator controller system. This system will comprise of a one deliverable25 kW motor controller system compatible of working together with theBoeing selected 25 kW motor / generator (rotor / stator). It is anticipated theflywheel controller will produce a variable frequency AC output from a 600-volt DC power source to drive the flywheel rotor assembly during the chargemode. During the discharge mode, the motor controller will take the AC outputof the 25 kW brushless DC permanent magnet motor / generator, on theflywheel rotor assembly, and convert it to volts DC; its value with respect tospeed.

2. The motor controller will be a stand-alone controller with a simple userinterface system capable of remote operation and monitoring; distance asgreat as 200 feet. Coordinate with Boeing engineering for remotecommunication bus choice. The control system will have to be self monitoringand fault tolerate. The motor controller will be packaged into an approvedcommercial type enclosure. Switching frequency harmonic reduction desired,to motor.

3. The motor controller will be required to operate the motor / generator in thefollowing modes of operation:

a. Startup (Charge) Mode: The system is not connected to the criticalload and is used for normal start up of the FESS. Hall Effectsensors are present to allow position indication until such time othersensing methods of control are suitable.

b. Normal (or Idle) Mode: The FESS is fully charged but is notproviding power to the load. This control method may utilize

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Sensorless Control or as specified. If another method of positionor speed sensing is desired, it is necessary to coordinate withBoeing engineering.

c. Discharge Mode: The FESS power system has now providing

power to the load. Intially, this mode will be controlled manually, i.e.automatic action between the Motor-Controller and LoadConditioning equipment will be defined by operators.

d. Recapture mode: After the FESS is partially discharged we restartthe motor drive action in a smooth and controlled fashion torecharge the FESS.

e. Normal Shut Down Mode: Used for normal shutdown of the FESS.This control method will require idling or disabling the drive controland manually loading the FESS with external loads.

f. Emergency Shut Down Mode: Used for a rapid deceleration of theflywheel rotor assembly during detection of an internal fault of theFESS. Energy is now diverted to external load bank.

4. The motor / generator controller design effort will be in coordination with theBoeing team to insure compatibility with the FESS motor / generator. Themotor / generator is Tau connected and operated as Delta wound, e.g.floating neutral.

5. Beginning engineering services within 5 days of receipt of contract willinclude: a preliminary data package consisting of physical properties such as

dimensions and weights: electrical characteristics such as reliability, voltageper phase, current per phase, electrical noise and shielding techniques; andother such characteristics or test data sufficient to commence with a finaldesign approval. The Boeing Company will respond to the preliminary datapackage within 5 days.

6. Final engineering services with 100 days of receipt of contract will includedelivery of one motor / generator controller system as well as engineeringservices to integration and tune the motor controller to the FESS motor /generator. Final engineering services will include documentation such asmechanical drawings, parts list, schematics, operating instructions, software,

and other test data used to verify the specifications outlined in Table 3.

SYSTEM SPECIFICATIONS

Table 3. Description of Inverter Characteristics.

Description of Inverter Characteristics Conceptual Design

Input Nominal Voltage600 Vdc

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Input Power Rating25 kWatts

Input Connection 2 wire plus ground

Input Voltage Range 500-670 Vdc

Input Current 60 Amps (RMS)

Input Power Factor 0.98 (at rated linear load)Speed Range 0-20,000 rpm

Output Rating at Critical Load 25Kwatts

Output Current 60 Amp (RMS)

Output Voltage 600 Vdc nominal at 20,000rpm

Output Voltage Regulation unregulated

Output Power Factor 0.7 lag to 0.9 lead

Output Harmonic Distortion 3-5% THD maximum over range of load

Output Ride Through Time 4 minutes

Other

Packaging Commercial Grade

Operating Temperature 40F to 120F

Motor Poles 6

Motor Phases 3

Testing of the Motor/Generator Controller required software additions,modifications and monitoring points. Specifically, the added visible monitor

points included many status variables previously suppressed, such that wecould not accurately diagnose some stability problems and operating modes.These parameters indicate the true operation of the Motor controller, i.e.torque vs. speed-loop and monitored conditions. Systematically, wedetermined that some control variables were incorrectly defined, yieldingerroneous operation and control. Range of variables affected proper control ofthe speed-loop, when initiated no acceleration and speed maintenanceresulted. Our software engineer examined the code and determined thecorrect ranges for the speed-loop control variables. Software additionscomprised of completion of the Speed-loop portion of the software (figure 21).This portion of the code is necessary to complete system integration, with

the UPS. Ultimately, the goal is to operate the flywheel under speed-loopcontrol via the three integrated program buttons provided on the UPS remotepanel, with automatic transitions. We are uncertain about the operation of thebasic sensor-less loop control blocks of software, i.e. Kalman Filter, SpeedEstimator etc. Timing analysis of the control loop software is not completedand tested. Once these operational parameters are established, the operatinglimits of the M/C will be defined. It has been determined that use of theTorque-Loop for operation is not desirable with this Controller and Motor-

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Generator (M/G) system, except for startup. Smooth operations under torquecontrol is limiting acceleration rate and is problematic. Thus, we have limitedour startup average current to 10 amps under Hall-Effect control and 20 ampsunder Current-loop Sensor-less control. We expect better control and higheracceleration under Speed-loop Sensor-less control.

Figure 21. Sensorless motor/generator control schematic.

The UPS tests accomplished insured basic autonomous function andcontrol of the interface and of its output power quality. This provided theknowledge necessary to prepare integrating the Motor Controller and UPS viathe Can Bus interface, and provide the necessary feedback and lessonslearned as a departure point for a new design. We verified operation usingour Variac to supply varying AC Power, for 'voltage range interlock' operationand load regulation. Additional software functions were added to provideremote monitoring of the UPS operation, on the Can Bus.

Efficient testing of this system requires an accurate bench test system todevelop the software. We used a small motor system from a previous system,but its pole number, stator inductance, and rotor inertia is very different than

the future flywheel system. Thus, bench testing and development is severelycurtailed and its effectiveness minimal. Even though rotor gaps andsuspension, of the motor, may differ in the future, the basic size andconstruction is essential. The system interface development should becentrally controlled, at the implementation site. Since the operation of thePower Risk Management System and motor/generator controller are similarand use like functions and components, a completely integrated system from

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a single supplier is desired in the future. This will avoid some of the multiplesupplier integration issues encountered during our Phase 2 activities.

Software completion requires substitution of code to replace the hardswitches currently used for startup, operation and shutdown. This codeneeds developing, testing and implementation into firmware, and then loaded

into the microprocessor. Current software versions do not include this portionof program code. Most of the basics blocks of code exist to test themotor/controller functions, although some untested, but an integrated versionis not complete. This code addition is required for future integration of thePower Risk Management System via the Can Bus interface in a commerciallydeployed, autonomously operated flywheel system.

final report boeing cooperative agreement no. de-fc36-02go12112 6-30-07

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