Pulsed Power Load Support - Hebner-Gattozzi - May 2010
- 1. Pulsed Power Loads Support and Efficiency Improvementon Navy ShipsR. E. Hebner, J. D. Herbst, A. L. GattozziCenter for ElectromechanicsUniversity of Texas, AustinMay 20, 2010
- 2. Statement of the ProblemIncreasing demand for reliable electric powerProjected expansion of pulsed loadsRising fuel costsTechnical SolutionsAdvanced power generation
- 3. Energy storage technologiesStudy for the DDG51 DestroyerHigh speed generators at 15,000 RPM 3 MW can be coupled directly to the gas turbineElimination of gear boxNew class of power electronics allows decoupling of the 60 Hz distribution frequency from the generated frequencyTurbine speed can be adjusted to maximize SFCEnergy storage provides additional benefits(details later)
- 4. Notional 3 MW Power Module
- 5. Benefits of StorageSupport of intermittent duty high power loadsLoad leveling (more efficient turbine operation)Power quality and stability improvementStiffer power busSingle turbine at near full load instead of two turbines at fractional loadsHigher efficiency & expanded engine operational hours Reduction of turbine thermal cyclingMaintenance reduction and operational life extension
- 6. Storage Technologies ConsideredCapacitorsLow energy density – not considered furtherBatteriesLi-ion technologyFlywheelsBatteries and flywheels competitive evaluation on several points follows
- 7. 1. Technology Readiness Level (TRL)Li-ion batteries:Preferred technology for low power electronicsSome developments in the kWh and kW (electric vehicles)No MW level application identified low TRLFlywheels:UPS system up to 1 MW in commercial use20 MW system being planned
- 8. 2. ScalingLi-ion batteries:3 MW 10 minute power delivery is difficultPractical packaging of large scale array is challengingLacking direct examples at these power levels, projections were made from installations with other battery chemistries
- 9. S&C PureWave UPS System2.5 MVA, 60 s, Lead-Acid Li-ion equivalent at 2.5 MW, 10 minutes = 121 m3
- 10. Alaska Golden Valley Cooperative Project27 MW, 15 min, NiCdLi-ion equivalent at 2.5 MW, 10 minutes = 116 m3
- 11. 3. Performance DegradationLi-ion batteries:Capacity fade (temperature and depth of discharge cycles)Energy capacity typically based on 1 hour discharge (1C rate)In our case 10 min discharge = 6C rate Higher internal resistance than other chemistries (higher heating)
- 12. 4. LifeLi-ion batteries:Short useful life relative to ship’s service lifeMay need to replace 3-4 times over 35 yearsSupport of pulsed loads and load leveling function will require frequent cyclesAsymmetrical charge / discharge rateFlywheels:Independent energy stored and power deliveryNASA study found no significant degradation after 110,000 deep discharge cyclesCan be designed for 35 years life
- 13. 5. ReliabilityLi-ion batteries:Low voltage of 3.6 V/cell 188 cells needed for 680 Vdc bus to generate 450 V 60 HzMany strings in parallel to supply needed currentSeveral thousand cells needed on boardFailure of single cell impairs the whole systemFlywheels:Based on standard rotating machine technology
- 14. 6. SafetyLi-ion batteries:Demonstrated catastrophic failure modeVery sensitive to charging voltage (4% maximum overcharge limit)New non-flammable electrolytes reduce energy and power by ~30%Complex cell monitoring system (eliminates failed cell from array)Based on all the issues above, flywheels are preferred technology
- 15. Flywheel StorageUpgrade main generator:Package the system in the current volume of the AG9140 Remove low speed generator and gearboxUse high speed generator and power electronicsIntegrate independent flywheel storage modules into existing power system:Flywheel + motor/generator + power electronics + auxiliaries
- 16. Stand-alone Flywheel Storage System(8 needed for 10 min. discharge)
- 17. Table 1. Physical Characteristics for 2.5 MW, 10-minute UPS Energy Storage System
- 18. Table 2. Electrical Characteristics for 2.5 MW, 10-minute UPS Energy Storage System
- 19. Simulation Study of Common DC Bus Topology
- 20. Simulation Studies: UPS Function
- 21. Response of AC Grid to Loss of Gas Turbine Generator Set at t = 0.75 sFlywheel Discharge and Recharge Cycles (Discharge (0-7 s) and Recharge (7-10 s))
- 22. DDG51 Fuel Saving EstimateBaseline parameters taken from BAA07-029: 4,000 hours of operation per year with a ship service power of 2525 kW (electrical) and a fuel cost of $100 per barrelTurbine specific fuel consumption for the AE1107 engine provided by Rolls-RoyceBaseline fuel consumption using current DDG51 CONOPS with two AG9140RF units providing the required 2525 kWProjected resulting fuel savings are $1.25 million per ship per year