Capacitive Electric Load Leveling Systems
Conceptual Design ReviewNovember 9, 2004
Erin Davis
Fred Jessup
Benton O’Neil
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Presentation Outline
• Customer Needs
• Key Research Issues
• Design Methods and Alternatives
• Deliverables
• Team Productivity
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Customer Needs
• Reduce vehicle weight
• Improve fuel efficiency
• Achieve system payback period of one year
• Demonstrate feasibility for tractor-trailers
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Key Research IssuesDetermined by Testing
• Battery– Starting requires high-
power density storage• Peak current ~600A• Large, heavy battery
• Alternator– Supplies current regardless
of engine load• Reduces engine efficiency
during heavy loading• If controlled, could improve
engine efficiency
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Possible Problems to be Addressed In Design
• Battery Problem– High power requires heavy lead acid
batteries– Non ideal charging and discharging
• Alternator Problem– Supplies current regardless of engine
mechanical load
• Both Battery and Alternator Problem
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Design #1 – Addresses Battery
• Converter controls discharging and charging of battery
• Capacitor bank assists in starting engine and supplies some peak current due to low ESR
• Battery current is normalized through control of DC/DC converter
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Scope Definition - Addressing Batteries
• Pros– Ultracapacitors are ideal for supplying high current– Feasible as bolt-on system – no internal vehicle signals needed – Significant decrease in weight with reduced battery size – Improved battery charging algorithm
• Increased battery life
• Cons– No direct fuel efficiency improvement– Ideal charging algorithm is difficult to determine– Bi-directional DC/DC converters
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Design #2 – Addresses Alternator
• Capacitor bank provides peak power through control of DC/DC converter
• Battery starts engine with assistance of capacitors
• Engine load due to alternator is normalized by switching algorithm
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Scope Definition – Addressing Alternator
• Pros– Direct improvement in fuel efficiency– Reduction in battery power and size
• Cons– Complex control system– Not feasible for bolt on system
• Need for engine load monitoring
– No guarantee of battery life improvement– High power DC/DC converter required
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Design #3 – Addresses Both
• Combination of Design #1 and Design #2
• Battery current normalized by DC/DC converter
• Engine load due to alternator normalized by switching algorithm
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Scope Definition - Addressing Both
• Pros– Increase in battery life– Increase in fuel efficiency
• Cons– Complex control– Large and complex system
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Initial Designs Decision Matrix
Weighting Factor Design #1 Design #2 Design #3
Benefit to Battery
0.15 1 3 2
Benefit to Alternator
0.05 3 1 2
Time to Complete
0.20 1 2 3
Cost 0.20 1 2 3
Weight 0.20 1 2 3
Size 0.10 1 2 3
Efficiency 0.10 1 2 3
Total 1.00 1.10 2.10 2.80
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Decision Matrix Results
• Focus on Design #1– Issues still needing to be address
• Ideal charging algorithm• Specific DC/DC converter selection
– Bi-directional versus unidirectional DC/DC converters– Buck, Boost, Buck-Boost
• Capacitor bank sizing• Battery sizing
– Physical – Power
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Design Focus ConclusionBattery: starting engine, weight issues
• Basic Operation– Caps start engine– Small battery charges caps though converter– Alternator charges battery
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Modeling
• Present system– Battery starting a 3.0L Lincoln LS engine
• Discharging Capacitors– Starting engine
• Charging Capacitors– Battery charging the capacitors through
different converter topologies
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Modeling Objectives
• Test different scenarios quickly, easily and safely• Compare design alternatives
– Capacitors• Size, capacitance, and weight• Maximum and minimum voltage, charging time, and usable energy• Peak current magnitude, engine speed, motor torque
– Converters• Control methods• Topologies
• Verify the design prior to implementation
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Simulink Output
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Capacitor Selection
• Using MathCAD– Parameters obtained from MAXWELL– Prices for set energy needed to start engine
Capacitor Pricing
Price_0350 216dollars Total_Weight_0350 1.19lb Charge_Time_0350 13.125s
Price_0013 175dollars Total_Weight_0013 3.351lb Charge_Time_0013 14.464s
Price_0008 444dollars Total_Weight_0008 6.173lb Charge_Time_0008 16.5s
Price_0010 606dollars Total_Weight_0010 8.102lb Charge_Time_0010 17.333s
Price_2500 300dollars Total_Weight_2500 11.188lb Charge_Time_2500 16.667s
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Converter Decision Matrix
Weighting Factor Buck Boost Buck-Boost
Energy Storage 0.40 3 1 2
Control Complexity
0.20 2 1 3
Low Voltage Charging
0.40 1 3 1
Total 1.00 2.00 1.80 1.80
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Preliminary Cost Analysis
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Remaining Design Choices
• Battery– AH rating necessary to supply loads during
engine off– Acceptable weight of battery
• Control– Analog vs digital
• Finalized converter topology
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Key Deliverables
• As of Now– Stock System Models– Preliminary Cost Analysis
• As of December 15, 2004– Design Description Report– Detailed Parts List
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Foreseen Challenges
• Design– DC/DC Converter– Control System Development
• Installation– Engine Heat Signature– Packaging
• Wiring, connections
– Vibration– EMI Shielding
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Team Productivity
• CELLS Team Webpage
• Project Status Reports
• Weekly meeting agendas / minutes
• Extracurricular Activities
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Questions?
