ultracapacitors for hybrid and electric vehicles - sae hev ev symposium 2013 rev5
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Ultracapacitors for Hybrid and Electric Vehicles
Shaw Lynds Dave Wright
Senior Systems Engineer Director, Application Engineering
SAE Hybrid & Electric Vehicle Technologies SymposiumFebruary, 2012
SAE Hybrid & Electric Vehicle Technologies SymposiumFebruary, 2012
What is an Ultracapacitor?
Ultracapacitors, Electric Double Layer Capacitors, Supercapacitors are all synonyms•Operating principle
An electronic charge accumulator having extreme capacitor plate specific area and atomic scale charge separation distance.
No chemical reactions during charge/discharge
•Performance 100k to >1M charge/ discharge cycles Up to 15 year DC life
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Graphic: IEEE Spectrum, Jan 2005
SAE Hybrid & Electric Vehicle Technologies SymposiumFebruary, 2012
Current Ultracapacitor Applications
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• AutoAuto• BusBus• RailRail
• WindWind• SolarSolar• Smart GridSmart Grid
• Solid State DriveSolid State Drive• UPSUPS
• CranesCranes• Fork LiftsFork Lifts• MiningMining• ConstructionConstruction
SAE Hybrid & Electric Vehicle Technologies SymposiumFebruary, 2012
Ultracapacitor Use in Hybrid Transit Buses
• Approximately 6000 hybrid transit buses are equipped with Maxwell ultracapacitors in Asia, Europe, and North America
• These systems typically use approximately three hundred 3000F cells in a variety of configurations
• Both series and parallel architectures have been implemented
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SAE Hybrid & Electric Vehicle Technologies SymposiumFebruary, 2012
System Block Diagram – Series/Parallel Hybrid
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Engine
UltracapacitorArray
MotorConverterChargerGenerator
DriveshaftTo Wheels
SAE Hybrid & Electric Vehicle Technologies SymposiumFebruary, 2012
Typical Usage Parameters
• European standardized transit bus cycle• UITP SORT1 – urban profile• Three accelerate/cruise/decelerate cycles
• System configuration• 288 cells of 3000F in series• 700V initial voltage
• Key performance metrics• Average power/cell 134W• RMS current 87A• Overall ultracapacitor efficiency 98%
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SAE Hybrid & Electric Vehicle Technologies SymposiumFebruary, 2012
Comparison to Other Hybrid Vehicles
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Toyota PriusVehicle mass: 1,400kgStored energy: 1,750WhAvailable energy: 175WhAvailable kinetic energy: 0-65mph
Ultracapacitor BusVehicle mass: 14,300kgStored energy: 845WhAvailable energy: 500WhAvailable kinetic energy: 0-35mph
60% Available
10% Available
Hybrid buses are designed for an urban drive cycle with low top speeds but a large number of cycles
The ultracapacitors have enough available energy to accelerate the bus to ~35 mph
For comparison, the Prius battery pack has enough available energy to accelerate it to ~65 mph
SAE Hybrid & Electric Vehicle Technologies SymposiumFebruary, 2012
Advantages of Hybrid Energy Storage
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A battery system must be sized for the peak power demand
An ultracapacitor system must be sized for the highest energy demand
A hybrid ultracapacitor and battery system can split these sizing requirements to allow the battery to meet energy requirements and the ultracapacitor to meet the peak power requirements
UltracapacitorBattery
When the power distribution for selected drive cycles are plotted vs. energy throughput, it can be seen that the power and energy distribution is not optimum for either a battery-only or an ultracapacitor-only system.
A battery system could be designed much more efficiently if it were not for the small amount of energy required at the peak power levels
An ultracapacitor system would be much smaller if it were not for the large amount of energy required at the lower power levels
The frequently proposed solution to this issue it to hybridize the two energy storage technologies. The open question is how much of the energy should be stored in the ultra capacitors.
SAE Hybrid & Electric Vehicle Technologies SymposiumFebruary, 2012
Sizing a Hybrid Energy Storage System
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We propose a system where the battery load is low-pass filtered to remove short-term events which can be handled by the ultracapacitors. The effectiveness of this approach can be modeled for selected drive cycles.
The lower power demand and Ah throughput for the battery would be expected to lead to much longer battery life
Alternatively the battery could be scaled down to achieve the same life with less stored energy
Conclusions: 5% of its total energy stored in ultracapacitors would reduce battery peak power by 50% and total Ah throughput by 40%.
SAE Hybrid & Electric Vehicle Technologies SymposiumFebruary, 2012
Summary
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Ultracapacitors have been successful with hybrid transit buses
Low top speeds Significant fuel savings from even a small
amount of energy storage Frequent stops and long operational hours
Energy storage with extremely high cycle life
The broader hybrid vehicle space could also benefit from energy storage systems with as little as 5% of their total energy in ultracapacitors
Reduce battery peak power requirements by 50% Reduce battery energy throughput by 40%