13 ortiz magnetic saturation of high power medium frequency transformers

7/31/2019 13 Ortiz Magnetic Saturation of High Power Medium Frequency Transformers

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Magnetic Saturation of High Power Medium FrequencyTransformers due to Semiconductor On-State Voltage Drop

and Switching Time Tolerances

Swiss Federal Institute of Technology (ETH) ZurichPower Electronic Systems Laboratory

. r z, . e a er, . . o ar

. . . .


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High-Power DC-DC Converters with MF TransformersHigh-Power DC-DC Converters with MF Transformers

In Renewable Energy GenerationIn Renewable Energy Generation High-Power DC-DC ConverterHigh-Power DC-DC Converterransm ss on o energy n .

Power flow control (Smart Grids).Reduction in size/weight.

ransm ss on o energy n .Power flow control (Smart Grids).Reduction in size/weight.

..

Reduction in size/weight.Increased efficiency.

Reduction in size/weight.Increased efficiency.

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The Dual Active BridgeThe Dual Active Bridge

Unmatched turn-on turn-off timesUnmatched turn-on turn-off times

Voltage is applied for a longer/shorter time inpositive and negative semi cycles.Voltage is applied for a longer/shorter time inpositive and negative semi cycles.

Different output characteristicsDifferent voltage levels are applied during the

Different output characteristicsDifferent voltage levels are applied during the

positive and negative semi cycles.positive and negative semi cycles.

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Result: Small DC component in voltages applied to the transformer !Result: Small DC component in voltages applied to the transformer !


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DC MagnetizationDC Magnetization

Equivalent circuit with independent DC and ACEquivalent circuit with independent DC and AC

DC component of magnetizing current

DC component of magnetizing current

DC component of magnetic flux densityDC component of magnetic flux density

Equivalent series resistance limits DC flux densityEquivalent series resistance limits DC flux density

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Example: 1MW / 20kHz TransformerExample: 1MW / 20kHz Transformer

Core-Type ConceptCore Material Vitroperm 500F (

r20000)Core-Type ConceptCore Material Vitroperm 500F (

r20000)

LV winding

( Primary)

LV winding

( Primary)MV winding(Secondary)MV winding(Secondary)

LV Winding Loss Optimized Copper Foil

Equivalent primary series resistanceRp,T= 6.8m

LV Winding Loss Optimized Copper Foil

Equivalent primary series resistanceRp,T= 6.8m

2 x U cut-core2 x U cut-core

Only 0.25ns of switching miss-match are enough to generate 0.2TOnly 0.25ns of switching miss-match are enough to generate 0.2T

Core&LV windingWater-cooledCore&LV windingWater-cooled

of DC flux density bias !of DC flux density bias !

Heatsink

Heatsink

Potted isolationbetween LV and MV

Potted isolationbetween LV and MV

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Magnetic Flux Density BalancingMagnetic Flux Density Balancing

PassiveSeries capacitor:A series capacitor prevents

any DC voltage on the transformer. However,

PassiveSeries capacitor:A series capacitor prevents

any DC voltage on the transformer. However,re uces power ens y an e c ency o e

system.re uces power ens y an e c ency o e

system.

Air-gap in magnetic path:An air-gap in themagnetic path reduces the equivalent

Air-gap in magnetic path:An air-gap in themagnetic path reduces the equivalentpermea y o e core. ere ore a component in the magnetizing current

generates a smaller DC flux density

component.

permea y o e core. ere ore a component in the magnetizing current

generates a smaller DC flux density

component.

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Magnetic Flux Density TransducersMagnetic Flux Density Transducers

Saturation DetectionE-core with air gap in external leg .

[R. Patel 1980]

Saturation DetectionE-core with air gap in external leg .

[R. Patel 1980]

Reduced cross-section and additional magnetic path.[J.A. Ferreira 1997]

Reduced cross-section and additional magnetic path.[J.A. Ferreira 1997]

Dynamic Flux MeasurementIntegration of applied voltage by external RC network.

[D. Wilson 1981]

Dynamic Flux MeasurementIntegration of applied voltage by external RC network.

[D. Wilson 1981]

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Magnetic Flux Density TransducersMagnetic Flux Density Transducers

Continuous Flux Density MeasurementMeasurement of magnetizing current.

[J.W. Kolar 2000]

Continuous Flux Density MeasurementMeasurement of magnetizing current.

[J.W. Kolar 2000]

Superimposed orthogonal flux density with external coil.S. Cuk 1982

Superimposed orthogonal flux density with external coil.S. Cuk 1982

Direct flux density measurement with hall sensor.Direct flux density measurement with hall sensor.

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Proposed FluxProposed Flux

easuremen oncepeasuremen oncep

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Proposed Flux Measurement MethodProposed Flux Measurement Method

ConceptShared magnetic pathbetween main core and an

auxiliary core.

ConceptShared magnetic pathbetween main core and an

auxiliary core.

Magnetic flux density through the main corechanges properties of the shared magnetic path,

Magnetic flux density through the main corechanges properties of the shared magnetic path,mo y ng , or examp e, t e n uctance seen rom t e

auxiliary core winding.

mo y ng, or examp e, t e n uctance seen rom t e

auxiliary core winding.

Auxiliary Core PlacementAuxiliary flux parallel to main flux density.

Auxiliary flux orthogonal to main flux density.

Auxiliary Core PlacementAuxiliary flux parallel to main flux density.

Auxiliary flux orthogonal to main flux density.

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Inductance MeasurementThe inductance L

auxmeasured on the auxiliary winding terminals decreases as the magnetization of

the main core increases.

Inductance MeasurementThe inductance L

auxmeasured on the auxiliary winding terminals decreases as the magnetization of

the main core increases.

This measurement was performed on aN27 FerriteE core and on aMetglas AMCC80 cut-core.This measurement was performed on aN27 FerriteE core and on aMetglas AMCC80 cut-core.

N27 E55 FerriteN27 E55 Ferrite Metglas AMCC80Metglas AMCC80

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ResultsThe cores were magnetized with a square shaped voltage.

ResultsThe cores were magnetized with a square shaped voltage.

e magne z ng curren s ows a e core s r ven o sa ura on.

Measurements show a clear relation between the measured voltage vm(t) and the magnetization state

of the core.

e magne z ng curren s ows a e core s r ven o sa ura on.

Measurements show a clear relation between the measured voltage vm(t) and the magnetization state

of the core.

N27 E55 FerriteN27 E55 Ferrite Metglas AMCC80Metglas AMCC80

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Magnetic Flux Density Active CorrectionMagnetic Flux Density Active Correction

Control SchemeThe signal from the magnetic transducer can be used to

actively correct the volts-seconds applied to the

Control SchemeThe signal from the magnetic transducer can be used to

actively correct the volts-seconds applied to therans ormer .

A central control unit adjusts the gating signals to

achieve the desired transferred power. Additionally, small

rans ormer .

A central control unit adjusts the gating signals to

achieve the desired transferred power. Additionally, smalla us men s are n ro uce o preven e sa ura on o e transformer core using the measurement from the proposedtransducer.

a us men s are n ro uce o preven e sa ura on o e transformer core using the measurement from the proposedtransducer.

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13 ortiz magnetic saturation of high power medium frequency transformers

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