thermal vs. power loss efficiency considerations for ... · for eddy current, minimize conductor...
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Christopher OliverNien Teng
Micrometals, Incorporated
Thermal vs. Power Loss Efficiency Considerations for Powder Core
Materials
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Outline Powder Cores Description What properties change with temperature Measurement Technique Sample Preparation Measurement Process
Permeability vs. Temperature Core Loss vs. Temperature Hysteresis Loss / Eddy Current Loss Model Measure / Model Each Seperately
Bsat vs. Temperature Greatest impact near Curie Temperature Negligible impact due to high Curie
Temperatures. Core Loss – Thermal Aging
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What is a Powder Core?
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Powder Core Characteristics Distributed Air gap Discrete gap not required – minimal Fringing Eddy Currents restricted to flowing within
particles “Soft” Saturation Flexible Material Choices Bsat Losses
Permeability controlled by Insulation Level
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What Properties Change with Temperature?
Reversible Changes Permeability
Dependent on Alloy System Both Quasi-Linear and Non-linear performance
Core Loss Effects on Hysteresis Loss Effects on Eddy Current Loss
Bsat Critical consideration of Ferrite Materials – Low Tc Minor impact on Powder Core Materials – High Tc
Irreversible Changes Core Loss – Thermal Aging
Does not impact most Alloy Cores Well characterized for Iron Powder Cores
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Sample Preparation:Wound and Drilled Sample
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Sample Preparation:Taped Sample
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Sample Preparation:Insulating Layer
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Sample Preparation:Ready for Testing
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Sample Preparation:Pre-heat / Pre-chill Sample
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Sample Preparation:Record Measurements
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Permeability vs. Temperature:Testing
Meter: Standard LCR meter Winding
Cover core uniformly – Minimize leakage Single Winding Minimize effect of Rdc and Rac
Frequency: In linear region for material (Q>20) Drive Level: For Initial Permeability, >1mT (10G) As Core heats/cools, Record Inductance, Temperature Verification: Meter drift, Slow Cooling Rate Convert to Inductance to Permeability Plot Permeability vs. Temperature Model the Relationship
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Permeability vs. Temperature:Typical relationships
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Permeability vs. Temperature:Testing
Part Number: SH-106125-2 High Frequency Sendust 125 Permeability
Winding: 10 turns #20 AWG (0.8 mm) Frequency: 1 MHz Meter: Agilent 4284A LCR Drive Level: 1V open Approximate Flux Density: 2 G (0.2 mT)
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Permeability vs. Temperature:Measured Values 125 perm High Freq. Sendust
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Development of Core Loss ModelCombining Hysteresis and Eddy Current Loss
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Measured Data and Fitted Steinmetz Coefficients
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Measured Data and Fitted Hys/Eddy Coefficients
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Core Loss vs. Temperature: Meter: Standard LCR, V-A-W meter or other Winding: Transformer (likely ignore IR drop, Conductor
Loss in calculation), uniform core coverage, minimize self capacitance
Frequency, Drive Level – Suitable for desired Loss component to dominate For Eddy Current, Minimize Conductor and Hysteresis For Hysteresis, Minimize Conductor and Eddy Current
As Core heats/cools, Record V, A, W, Temperature Verification: Meter drift, Slow Cooling Rate Plot Core Loss (Hys. or Eddy) vs. Temperature Model the Relationship
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Core Loss (Eddy Current) vs. Temperature:Testing
Part Number: SH-106125-2 High Frequency Sendust 125 Permeability
Winding 10 turns #20 AWG (0.8 mm) Frequency: 1 MHz
Meter: Agilent 4284A LCR Drive Level: 1V open Approximate Flux Density: 2 G (0.2 mT) Calculated Loss Distribution (Room Temp.) Conductor Losses: 1.2% Hysteresis Losses: 1.6% Eddy Current Losses: 97.3%
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Q vs. Temperature MeasurementsSH-106125-2 – 1 MHz
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L/Q vs. Temperature SH-106125-2 – 1 MHz
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Eddy Current Coefficient vs. TemperatureSH-106125-2 – 1 MHz
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Eddy Current Coefficient vs. TemperatureSH-106125-2 – 1 MHz
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Core Loss (Hysteresis Loss) vs. Temperature
Part Number: SH-106125-2 High Frequency Sendust 125 Permeability
Winding 20 turns #20 AWG (0.8 mm) Primary 20 turns #22 AWG (0.63 mm) Secondary
Frequency: 5 KHz Meter: Agilent Clarke Hess 258 V-A-W meter Drive Level: 5 Vrms across secondary Approximate Flux Density: 1790 G (0.179 T) Calculated Loss Distribution (Room Temp.)
Conductor Losses: Ignored – No current flows in Secondary Hysteresis Losses: 98.9% Eddy Current Losses: 1.1%
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Hysteresis Loss vs. TemperatureSH-106125-2 – 5kHz
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Hysteresis Loss vs. TemperatureSH-106125-2 – 5kHz
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Core Loss vs. Temperature Summary
Part Number: SH-106125-2 For Temperature going from 25°C to 125°C: Eddy Current Loss decreases by 25% Hysteresis Loss increased by 66%
To know true effect, one must know the distribution of losses at a given operating point
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Thermal Aging:• What is thermal aging? When Iron Powder is subjected to prolonged
exposure to elevated temperatures, an irreversible increase in core loss is experienced
• What influences the rate at which the core loss increases versus time? There are 6 variables that all interact with each
other. Changing any one variable will change the rate at which thermal aging occurs
Most Alloy Powder Cores do not experience Thermal Aging
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Thermal Aging:
6 variables influencing thermal aging:• Core Material• Peak AC flux density• Frequency• Core geometry• Copper loss• Ambient temperature
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Thermal Aging: