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. Sullivanchrs@dartmouth.edu

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

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

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

WIRELESS POWER TRANSFERNew topic

9sites.dartmouth.edu/power-magnetics/

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/

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/

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/

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/

Operation principle – single section Each section:

Inductive current loop

Capacitive connection between foil layers through dielectric

14sites.dartmouth.edu/power-magnetics/

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/

Current flow path illustration

160° 180° 360°

Shown in an “unwound” stack.

Capacitive ballasting enables equal current sharing.

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/

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/

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/