Power for a Wireless World Measuring Wireless Charging ...
Transcript of Power for a Wireless World Measuring Wireless Charging ...
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Power for a Wireless World
Measuring Wireless Charging EfficiencyIn the Real World
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Power for a Wireless World
Or…Why a Wireless Charging Spec
needs to Support Close & Loosely-Coupled Approaches
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Power for a Wireless WorldPower for a Wireless World
Industry-Wide Problem:
There is no Standardized test methodology for specifying power
efficiency of a wireless charging system
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WPT Receiver
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Power for a Wireless WorldEfficiency
Matters
• Who cares about efficiency?• IKEA• McDonald’s• EPA/China/EU/ Gov’t agencies• Auto makers• Consumers• Who doesn’t care?
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Power for a Wireless World
1. DC out A: Not a valid representation of real-world application2. DC out B: A good proxy, if the right load range is selected3. DC out C: The real-world view, also allows complete energy
analysis
No Measurement
Standard
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DC OutC
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WPT Receiver
DC OutA
DC OutB
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Power for a Wireless World 2 Architectures
Rezence perimeter coil Qi planar coil
Resonant Inductive
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Power for a Wireless WorldArchitecture
Comparison
Architecture Representative Standards
OperatingFrequency
AntennaStructure
Benefits1
ResonantAKA: Loosely Coupled
• Rezence • 6.78 MHz Perimeter • Extended Z-distance• Multi-device
InductiveAKA: CloselyCoupled
• Qi• PMA
• 110 ~ 205 kHz• 200 ~ 300 kHz
Planar • Highly efficient• Low cost
Question: Why not use resonant architecture for all applications?Answer: Efficiency and cost tradeoffs make it inappropriate to do so.
1. There are no Rezence products in the market, so benefits are as per the promotional materials from the A4WP
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Power for a Wireless World
Use-Case
Examples
Resonant: Under-surface mount
Inductive: Automotive
Inductive: Charging Stand
Inductive: Charging Plate
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Power for a Wireless World
Ideal Definition of Efficiency
Efficiency should be calculated as spatial average:
“Total joules into the battery divided by total joules into the transmitter averaged over the charge area/volume for a charge
cycle”
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Power for a Wireless WorldWhere is Efficiency
Measured?
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DC In
AC Adapter
Wireless Transmitter
Wireless Receiver
Efficiency Measurement
Taken at the optimal spatial position and load power (5W, 4.2V @ 1.2A)
DC out
AC
DC
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Power for a Wireless WorldEfficiency
Experiment
1. Loosely-coupled, high-frequency wireless charger
– EPC-9112
– Similar to A4WP/Rezence Class 3
– 6.78 MHz operation
2. Closely-coupled, low-frequency wireless charger
– BQ500212
– Qi spec 1.1.2, Type A11
– 110 ~ 210 kHz
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Power for a Wireless WorldBattery Model:
2100 mA hr.
Model determines load resistance, voltage and current test conditions
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Power for a Wireless WorldTotal Energy
27 kJ
Energy required for typical (90%) charge-cycle of a 2100 mA hr. battery
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Power for a Wireless World
6.78 MHzG
aN
Dri
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5Vout
VDD
8V – 36V
Gate Drive & Control
7.5V
Synchronous buck pre-regulator
LDO
GaN
Zero Voltage Switching Class D Amplifier
Efficient Power ConversionEvaluation Kit EPC9112
• 6.78 MHz operation• GaN switches• ZVS, Class D amplifier• NuCurrent antenna system
compliant to Rezence class-3
Rload
EPC Device Board(Receiver)
High-Frequency Wireless Charger Efficiency Experiment
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Power for a Wireless World
Efficiency vs. position for 10 ohm load“Open-Loop”
Spatial Position Matters
Rload
EPC Device Board(Receiver)
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Power for a Wireless World 2 Configurations
Rload
EPC Device Board(Receiver)
Rload
EPC Device Board(Receiver)
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Resistive Load Configuration
Battery Charging Configuration
0V - >40V
5.0V
0V - 28V
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Power for a Wireless World
Texas InstrumentsEvaluation Kit bq500212
• 100 ~200 kHz operation• CMOS switches• Würth antenna compliant to
Qi A11
Low-Frequency Wireless Charger Efficiency Experiment
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Power for a Wireless World
Efficiency vs. position for 5 ohm loadFull System
Spatial Position Matters
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Power for a Wireless World
Efficiency Test
Results
• Qi is the most efficient system by design
• Efficiency is impacted by:• Switching frequency• Antenna design• Spatial position / Coil-
coupling coefficient• Maximum Power-
Point Transfer
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Power for a Wireless WorldBattery Model:
2100 mA hr.
Total energy over 5% to 95% charge cycle: 27 k Joules
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Power for a Wireless WorldReal-World Efficiency
Total Energy EfficiencyQi = 59.4%
Rezence = 39.6%
27 kJh= 100%
43.8 kJh= 59.4%
65.7 kJh= 39.6%
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Power for a Wireless World Conclusions
• Real-world conditions must be used
• Efficiency should be defined as a spatial average based on real-world use
– “Total joules into the battery divided by total joules into the transmitter over one charge cycle”
• Qi (low-frequency system) total charge efficiency ~60%
• High-frequency total charge efficiency ~40%
• A wireless charging standard that meets all market needs and use-cases must be dual-mode (resonant & inductive)
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Power for a Wireless WorldPower for a Wireless World
Thank You