Rotating Machines as Energy Storage and Power Management Systems

Mike Werstm.werst@cem.utexas.edu

February 10, 2010

Electric Power

Space

Transportation

• Advanced Generators

• Electric Grid Control

• Energy Storage

• Distributed Generation

Technology

• Advanced Trains

• Hybrid Vehicles

• Active Suspension for Vehicles

• Wheel Motors

• Intelligent Highways

• Space Power

• Electromagnetic Launch

• Satellite Attitude Control

Defense• Missile and Aircraft Launcher

• All Electric Ship

• Advanced Wheeled and

Tracked Vehicles

• Electromagnetic Guns

• Electromagnetic Armor

Oil & Gas• Exploration• Transmission

Biotech• Electromechanical cell

manipulation

Areas of TechnologyVG 12983a

Flywheel Energy Storage

*Holm et. al., “A Comparison of Energy Storage Technologies as Energy Buffer in Renewable Energy Sources with respect to Power Capability.”

Wikipedia definition: “A flywheel is a mechanical device with a significant moment of inertia used as a storage device for rotational energy.”

Flywheels have a much broader range of usage than given credit for.

Kinetic Energy

*Burr, “Mechanical Analysis and Design, 1981

Specific Strength of Selected Materials

Flywheel energy storage efficiency is dependent on material and mass distribution

Flywheel Highlights

• Conducted flywheel tests, including

– Flywheel only tests to identify failure modes and structural margins

– Flywheel burst tests to test candidate containment designs

• Demonstrated life of more than 110,000 cycles with a 50% DOD

Containment System

MagneticBearings

Gimbal Shaft

Motor Generator

Composite Flywheel

Backup Bearings

VG 12973e

Flywheel Challenges• Losses

– Vacuum air gap significantly reduces windage losses at the price of vacuum pump auxiliary

– Bearings• Roller bearing require lubrication• Magnetic bearings expensive and require touch-down bearings• Superconducting bearings need development

• Carbon fiber material and manufacturing cost– Demand for high modulus/high strength carbon fiber– Industrial participation/competitiveness will bring mfg cost down

• Flywheel safety– Design margin– Flywheel health monitors/fault protection– Containment

Kinetic Energy Storage

Application dictates flywheel topology that meets energy and power requirements

VG 12973a

Non-Integrated Topology Partially-Integrated Topology Fully-Integrated Topology

Flywheel Spin Tests• Flywheel tests to-date:

– Numerous burst tests (modified design for containment proof tests)

– Loss of vacuum test– Over-speed “As Built” Test

- Preload loss- 1120 m/s- Benign and recoverable

– Coupon/Fatigue tests

VG 12973f

Hydroburst test coupon High temperature & pressure autoclave

4-axis filament winder

Multi-ring preloaded flywheel

Technical Successes - Flywheel

• Record tip speed for composite flywheel/arbor assembly (1.34 km/s)

• Key features – Composite structural arbor design – Detailed material and

manufacturing process QA

VG 12973g

Parameter NASA FESS ALPS System Bus System CHPS SystemFunction Energy Storage Load Leveling Load Leveling Leveling/Pulsed

Energy Stored (kWhr) 3.6 133 2 7

Peak Power (kW) 5 2,000 150 5,000

Typical Discharge Time 30 minutes ~ 3 minutes 30 seconds 3 seconds

Rotational Speed (RPM) 53,000 15,000 40,000 20,000

Machine Weight (lbs) 250 19,000 450 1,100

Motor/Generator Permanent Magnet Induction Permanent Magnet Permanent Magnet

Topology Partially Integrated Non-Integrated Partially Integrated Fully Integrated

Cooling Cold Plate Air/Oil and Water Oil and Water Oil

Bearings Homopolar Magnetic Hompolar Magnetic Homopolar Magnetic Homopolar Magnetic

Backup Bearing Duty Limited Limited Significant Significant

Gimbal NA (Torque Balanced) Required Required Required

Flywheel Design CEM Cylindrical CEM Cylindrical CEM Cylindrical CEM Mass Loaded

Rotor Tip Speed (m/s) 920 1,015 935 600

Safety RSL&NDE RSL & Containment RSL&Containment RSL

Designed DesignedBuilt & tested

Built & tested

CEM Flywheel Comparison

FW Battery (+ Electronics) (+ Electronics)

Nominal Power 4.1 kW 4.1 kWPeak Power 6.6 kW 6.6 kWEnergy Delivered 5.6 kW-hr 4.6 kW-hrContingency Power 2 orbits 1 orbitLife Expectancy >15 years 5-6 years

Flywheel Energy Storage System for the International Space Station (FESS)

• Operations advantages– Higher round trip efficiency– Known state-of-charge– Offer more flexibility in

charge/discharge profiles– Doubled contingency power

(energy)

• Significant life cycle cost savings– Reduced logistics (up-mass & down-mass)– Reduced maintenance (EVA- IVA Hr/Yr)

Advanced Locomotive Propulsion (ALPS) Program Flywheel

• electrical load leveling for hybrid electric locomotive

• flywheel stores 480 MJ• @ 15,000 rpm• 2 MW motor/generator – ~3 min discharge

• Testing with high input and output power

VG 12973h

Backup BearingsRadial BearingStator WindingPermanent Magnet RotorComposite Flywheel

Combo Bearing

Transit Bus FlywheelEnergy Storage:

Power:2 kWhr stored, 1 kWhr delivered150 kW peak, 110 kW cont.,Between 30,000 and 40,000 RPM

Composite tip speed:Application:

930 m/s at 40,000 rpmPower averaging for 15 tonHybrid Electric Bus

Permanent Magnet

AluminumCeramic

WindingsTitaniumInconelCompositeStainless SteelSteel

Materials

CEM Flywheel Energy Storage Systems for Military Applications

VG 11536.ppt

Electromagnetic Aircraft Launch System (EMALS) Energy Storage System

(2006)

Iron Core Pulse Alternator800 MW, 10.5 kW-h

(1987)

Composite Rotor Pulse Alternator664 MW, 2.5 kW-h

(1991)

S 4101.0607

S 3010.1993

Composite Rotor Pulse Alternator2.4 GW, 11 kW-h

(1995)

S 3910.1748

Composite Rotor & Stator Pulse Alternator3 GW, 6.4 kW-h

(1997)

?

Current EM Gun Power SupplyResearch is Ongoing at CEM

(2009)

Homopolar Generator (HPG) Flywheels• Faraday disks• 1/10s to 10s of second discharge rates• Very high current/low voltage machines• CEM HPGs used for variety of applications

– Large x-section resistive welding—12” sch. 60 pipe welds– Railguns—90mm, 9MJ muzzle energy – High-field, single-turn magnets—9MA, 20T toroidal magnet

60 MJ HPG Set—6 ea, 100V, 1.5MA/gen

All Iron Rotating (AIR) HPG6.2 MJ, 50 V, 750 kA

Flywheel vs. Electrochemical Energy Storage

100,000 1,000,000

1 236

4

5

9

10

11

12

13

7

8

Summary

• Advanced carbon materials and manufacturing methods enable– Energy densities comparable to chemical storage devices– Extremely high power densities for pulsed power applications

• Flywheels capable of wide range of energy storage applications: .01s to 1800s

• Many challenges have been overcome: additional R&D could improve energy storage capacity, efficiency and usage