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?