beyond conventional wireless power transfer and education of … beyond... · 2019. 8. 21. ·...
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Dartmouth Magneticsand Power ElectronicsR e s e a r c h G r o u p
Power Management Integration Center
PMIC
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Beyond Conventional Wireless Power Transfer and
Education of Electrification Engineers
Charles R. [email protected]
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Two topics
Education of Electrification Engineers Formula Hybrid competition.
Hands-on class: Practical Electrified Vehicle Engineering.
Wireless power transfer Challenges for conventional
resonant inductive WPT.
Potential of new high-Q self resonant structure.
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Competition for college students to build and race hybrids and EVs.
Founded and run by Dartmouth with IEEE and SAE.
42 Sponsors include Fiat Chrysler, Ford, General Motors, LG Chem, BAE Systems, AVL, and Toyota.
Since 2007,
3500 students competed
250 cars designed
from 80 universities (54 US, 26 international)
ABET innovation award, 2018
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Goal: Education
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Mechanical and electrical engineers work together on a complex system.
Multiple design objectives including race performance, efficiency based on limited fuel allocation, and reliability.
Theory and practice need to come together through teamwork and effective project management
Working within constraints: rules, safety.
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Individuals: volunteer as an official at the event (May in NH), on the rules committee, or as a team mentor.
Industry: sponsors gain visibility and access to recruit excellent students.
Academics: encourage your students to form a team.
http://formula-hybrid.org/
Opportunities
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Practical EV engineering course
Hands-on undergraduate course.
Designed to compliment other educational opportunities:
Formula Hybrid competition.
Classes in systems, electrical design, mechanical design, power electronics, energy ultilization, etc.
Emphasis on engineering basis of:
Practical construction
Safety
Secondary topic: Propulsion system design, operation and optimization.
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Electrical review, interfacing, motors.
High-power electrical implementation and safety.
High current electrical connections
Current safety issues: Conductor ampacity and fusing
Voltage safety issues: insulation and shock hazards
Mechanical systems implementation
Battery and super-capacitor systems
Thermal management
Vehicle system design and analysis
Specific Topics
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Example exercises Fuses:
Measure melt time.
Explode with > rated voltage.
Bolted connections:
Resistance vs. torque
Effects of thermal expansion and oxidation
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6101 aluminum 1100 aluminum
30% increase
16,000%increase
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WIRELESS POWER TRANSFERNew topic
9sites.dartmouth.edu/power-magnetics/
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Wireless Power Transfer: Challenges
Resonant inductive WPT can work well, but challenges include:
Need very high resonant Q to get high efficiency.
Conventional approach: litz wire.
Expensive
Super-fine strands needed for high Q at high frequency.
Capacitor losses, high resonant voltages at high power, thermal limits …
10sites.dartmouth.edu/power-magnetics/
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Foil instead of litz: < 20 µm at low cost
Easy to get thickness << skin depth.
Freestanding foil down to ~ 6 µm.
On plastic-film substrates for ease of handling to << 1 μm.
Thin layers have high dc resistance—need many in parallel.
Challenges:
Achieving uniform current density—laterally and among layers.
High capacitance between layers.
Terminations
11sites.dartmouth.edu/power-magnetics/
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Concept for parallel foil windings: capacitive ballasting
Overlapping insulated layers create series capacitance for each layer.
Capacitive ballasting forces equal current sharing.
Can create integrated LC structure, a concept with a long history.
In addition to integration, solves winding loss challenges.
Port 1
Cartoon: real structures have many more layers
12sites.dartmouth.edu/power-magnetics/
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Resonant structure for wireless power
Many stacked layers with no vias and no terminations.
Current sharing between many thin layers enforced by same capacitance used for resonance.
13sites.dartmouth.edu/power-magnetics/
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Operation principle – single section Each section:
Inductive current loop
Capacitive connection between foil layers through dielectric
14sites.dartmouth.edu/power-magnetics/
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Operation principle – many sections Strong mutual coupling between all layers.
Each section capacitance is coupled to form a parallel LC resonator.
Coupled section capacitance forces equal current sharing in each layer.
Integrated capacitance eliminates high current terminations.
Experimental Q = 1180 with 66 mm diameter.
> 6X improvement over state of the art.
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Section
Section
sites.dartmouth.edu/power-magnetics/
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Current flow path illustration
160° 180° 360°
Shown in an “unwound” stack.
Capacitive ballasting enables equal current sharing.
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Wireless power transfer efficiency versus distance
Experimentally validated wireless power transfer between two modified self-resonant structures
2x range with η > 94%
η > 80% at 7.5 cm
η = 98.8% at 2.2 cm
Tested up to 400 W.
ηmax based on state-
of-the-art Q
Structure diameter
Experimental
WPT data
ηmax Modified Self-Resonant Structure
sites.dartmouth.edu/power-magnetics/
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Self-resonant wireless power transfer structures
Better Q means better range/higher power
Can use thin foil effectively.
No external capacitor means no added plate loss; no termination loss.
Lower voltages with a single-turn coil.
6.6 cm coil: Q > 1000, 6.78 MHz.
Larger higher power larger coils will be easier to build.
Commercial applications under development by Resonant Link, LLC.
18sites.dartmouth.edu/power-magnetics/
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Summary
Formula Hybrid competition motivates and challenges students to collaborate across disciplines, manage a complex project, and carry out a reliable, practical implementation.
Practical electrified vehicle course: Hands-on introduction to engineering basis of EV construction and safety to complement other coursework.
Wireless power transfer: New self-resonant structure has 6X higher Q than conventional coils, for higher efficiency and/or longer range.
19sites.dartmouth.edu/power-magnetics/