Wireless Charging of Electric Vehicles Using Strongly Coupled Resonance

Wireless Charging of Electric  Vehicles Using Strongly‐Coupled Resonance Morris Kesler WiTricity Corporation National Electric Transportation Infrast...
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Wireless Charging of Electric  Vehicles Using Strongly‐Coupled Resonance Morris Kesler WiTricity Corporation

National Electric Transportation Infrastructure  Working Council

Outline • Motivations • Introduction to WiTricity’s Technology – Resonance – Coupling and Quality Factor

• Application to EV/PHEV Charging – System description – Performance – Issues IWC 2012

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In the Middle of the Night…

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From the Wall Plug to the Device Approaches to Wireless Energy Transfer Radiative techniques

Induction

Omni-directional

Directed IWC 2012

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Add Resonance to the Picture • Resonator: – Stores Energy – Energy oscillates between two modes (spatial,  temporal, form, etc.) – Examples: Pendulum, Quartz crystal, LC Circuit

• Coupled Resonators: – Coupling mediates energy exchange between  resonators – Efficient and selective energy transfer can be  achieved – Examples: Coupled pendulums, coupled  waveguides (filters, switches) IWC 2012

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Coupled Resonators • Described using coupled‐mode theory – Parameters: Coupling rate (κ), loss rate (Γ),  resonant frequency

• Conditions for efficient energy transfer – “Similar” resonant frequencies – Coupling rate greater than loss rate

• Figure of Merit for system – U = κ/sqrt(Γ1Γ2) = k*sqrt(Q1Q2) – Optimum efficiency only a function of U IWC 2012

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Efficiency of Energy Transfer 90% at U=20

Optimum efficiency only a function of the figure-of-merit U η=

50% at U=3

(1 +

U2 1+U

2

)

2

where U=

κ Γ1Γ 2

= k Q1Q2

Coupling and Q are important factors

Resonators with High Quality factor enable efficient energy transfer over distance. IWC 2012

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Using Magnetic Resonance Coupled Magnetic Resonators

• Magnetic resonator – Simple example is a  loop and capacitor

B

E IWC 2012

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A Multitude of Applications

Consumer Electronics Medical Devices Electric Vehicles

Robotics

Solar Power

Lighting

New applications are limited only by one’s imagination IWC 2012

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Residential Use Case

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Requirements for Wireless  Charging of EV • Power levels up to 3.3 kW  (initially) • High‐efficiency (90% end‐to‐end) • Tolerant to parking variations • Tolerant to variations in vehicle  ground clearance (vehicle loading,  tire pressure, etc.) • Safely operate with people in and  around vehicle • Satisfy EMC/EMI requirements • Safe, unattended operation IWC 2012

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Resonators designed for high Q and coupling, efficient power electronics Efficiently operate over a range of magnetic coupling

EM fields below ICNIRP limits where accessible Low radiated EM fields, Choice of frequency Detection of foreign objects, Built-in temperature sensing 11

System Components for Wireless  EV Charging Device Electronics

Device Resonator

AC/DC (Rect.)

Battery

Source Electronics Mains Power

BMS AC/DC (PFC)

RF AMP (DC‐RF)

Source Resonator Control

Source Efficiency > 95%

Wireless Efficiency 90 – 98.5%

Rectifier Efficiency > 99%

AC Mains to Battery Efficiency of greater than 90% possible IWC 2012

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Tolerance to Offsets Parking Tolerance Direction of Travel

Air-Gap Variations

Source Resonator

Δz Device Resonator

Source Resonator

Δy

Typical ranges: Δx

Δx up to +/- 20 cm

Device Resonator

Δy up to +/- 10 cm Δz up to +/- 2.5 cm

Systems must operate at high efficiency over this range of offset. IWC 2012

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Magnetic Field Strengths •

Zone 1: Energy Transfer Region – Largest B field – No prolonged human exposure



Zone 2: Under Vehicle Region – B rapidly decreasing – No prolonged human exposure



Zone 3: Exterior Region – B < ICNIRP MPE – Unlimited human exposure



Zone 4: Vehicle Interior – B < ICNIRP MPE – Unlimited human exposure

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Foreign Object Debris • Magnetic field in energy transfer region (between coils)  is large – Maximum field depends on coil design and size – Can cause heating of some metallic objects

• Examples of likely debris

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Detection of Foreign Object Debris • Two Basic Approaches • Passive techniques: – Reduce likelihood of FOD interacting hazardously with high  magnetic fields. – Large coils to reduce peak B field – Shaped structures

• Active techniques: – Detect and react to the presence of FOD. – Reduce power or interupt charging – Scales to higher power 

• WiTricity prototype FOD detection system demonstrated – http://www.youtube.com/watch?v=my5fvOh15kg

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WiTricity Prototype System

Standard Capture Resonator

Rectifier

Standard Source Resonator Integrated Power Supply (Level 2) (1)

Standard Resonator Configuration (10-15cm or 15-20cm offset) IWC 2012

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WiTricity 3.3 kW Prototype On‐Vehicle Installation , June 2010

IMS Workshop 2011

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Electric Smart Car Demonstration Device Coil mounted on Car

Source Coil on Floor

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Wireless Charging for EV/PHEV is Coming High efficiency ( > 90%) High power rates (3.3 kW and greater) Power transfer over several tens of cm “Robust” to:  misalignment, weather, vehicle  materials, building materials • Safe operation in residential, commercial, and  municipal configurations • • • •

Availability of wireless charging will increase adoption rates for EV/PHEV IMS Workshop 2011

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