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...
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
WiTricity Corporation
2
In the Middle of the Night…
IWC 2012
WiTricity Corporation
3
From the Wall Plug to the Device Approaches to Wireless Energy Transfer Radiative techniques
Induction
Omni-directional
Directed IWC 2012
WiTricity Corporation
4
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
WiTricity Corporation
5
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
WiTricity Corporation
6
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
WiTricity Corporation
7
Using Magnetic Resonance Coupled Magnetic Resonators
• Magnetic resonator – Simple example is a loop and capacitor
B
E IWC 2012
WiTricity Corporation
8
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
WiTricity Corporation
9
Residential Use Case
IWC 2012
WiTricity Corporation
10
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
WiTricity Corporation
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
WiTricity Corporation
12
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
WiTricity Corporation
13
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
IWC 2012
WiTricity Corporation
14
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
IWC 2012
WiTricity Corporation
15
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
IWC 2012
WiTricity Corporation
16
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
WiTricity Corporation
17
WiTricity 3.3 kW Prototype On‐Vehicle Installation , June 2010
IMS Workshop 2011
WiTricity Corporation
18
Electric Smart Car Demonstration Device Coil mounted on Car
Source Coil on Floor
IMS Workshop 2011
WiTricity Corporation
19
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