enabling pressure tolerant power electronics - …...1 findings and interim conclusions from 10...

Technology for a better society

[email protected]

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Findings and interim conclusions from 10 years of research at

SINTEF Energy Research

Enabling Pressure Tolerant Power Electronics - PTPE

for Deep Water Applications

Technology for a better society 2

Two Research projects at SINTEF Energy Research on

Pressure Tolerant Power Electronics

PTPEPressure TolerantPower Electronics

• 2006-2012: “Feasible power electronics for demanding subsea applications”– Financed by The Research Council of Norway

and 7 industry partner

• 2012-2016: "Pressure Tolerant Power Electronics for Subsea Oil and Gas Exploitation – PressPack– Financed by The Research Council of Norway

and 9 industry partner

• Main objective for both projects:– Provide fundamental material and packaging

knowledge for supporting realisation of reliable pressure tolerant power electronic components and circuits

– Reliable operation up to 500 bar ambient pressure, corresponding to 5000m sea depth


This Presentation

Examples of subsea converter applications and power circuits

Converter circuitry and components

Potential advantages by PTPE

PT packaging challenges

Strategy for the research

Test objects, test facilities and test programs

Interim findings and conclusions

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Some subsea electric power converter applications

• Power supplies for control and monitoring

• Valve actuators

• Emergency power (UPS)

• Energy storage conversion

• Variable speed motor drives

• Pipeline heating systems (DEH)


Q

P

V,I,f

Tr D

DTr

Tr

DTr

Tr D

DTr

V

W

U

D

2

1

DC-link

V

A general 3-phase AC/DC converter

• Bidirectional active power flow• Bidirectional reactive power flow• Very fast transition

Switching devicesDC-linkcapacitor bank

Filter reactors


IGBT - Insulated Gate Bipolar Transistor

• Today the most common switching device

• Various encapsulations

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• A 750A/ 6500V IGBT module from Infineon

• A 1800A/ 4500V hockey puck type

• press-pack IGBT from Westcode

• 1000A/4500V StakPak

• press-pack IGBT from ABB


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module #1

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module #2

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module #n

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[H]

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module #1

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module #1

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Vdc

Modular Multilevel Converter - MMC

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Converter topologies for higher voltage levels

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Vdc_Sub

IGBT_1

IGBT_2

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DTr

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DC-link

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U phaseVdc

2L-VCS (one phase-leg)

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Series connectionof IGBTs

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Vdc/2

U phase

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Neutral

point

3L-VCS (one phase-leg)

Due to voltage limitation of single power semiconductors , high voltage converters need more complex topologies and/ or series connection of IGBTs

Single devices limited by voltage and current rating


• Reduced weight and volume

Reduced container wall thickness

Full freedom for shape of container, e.g. flat constructions

Less filler material (liquid)

• Reliability and cost

Natural cooling possible

No moving parts (pumps, fans)

Reduced number of pressure penetrations

Reduced risk for leakage

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Potential advantages by pressure balanced solutions

Pressure balanced construction with direct conductive heating

through walls of vessel


Pressurized converter power circuit

Dr.

Dr.

Driver Driver

SensorsV, I, T, P,H

Converter driver and sensor interface Aux. power

Dr.

Dr.

Dr.

Dr.

One bar compartment forconverter central control

1-300 bar liquidenvironment

IGBT driverswith electric or optic interface

Pressure barrier


• Identify the most critical components of a power electronic converter

Power semiconductors, DC-link capacitors, IGBT gate drivers

Auxiliary power supplies, I,V, P,T sensors etc. assumed to be located in pressure compartment

• Provide roadmap for the experimental work

Involving component and material manufactures

Provide custom made test objects

Provide the required special equipment for the experimental work

• Component material experiments

Electric insulation properties

Chemical compatibility

• Single components experiments

Passive tests and live tests

• Converter power modules

Live operation up to rated power for the components

With the most critical power components

Insulation tests, Pulse testing and Continuous operation

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Focusing the assumed most critical power components


Summary of pressure tolerant packaging challenges

• Mechanical stress to encapsulations caused by the high pressure environment, and also possibly due to vacuuming processes in connection with filling.

– Dedicated experiments in pressure vessel with high pressure slew rates

• Possible change of functionality and characteristics of semiconductors due to pressure

– Such as changes in switching performance due to impact on driver electronics and/or directly on IGBT parameters.

– Live experiments with high voltage converter modules in pressure vessels

– Including IGBTs, driver electronics auxiliary supply, sensors etc.

• Impact from the pressurized environment on the "self-healing" performances of PP-film capacitors.

– Live testing of components according to established procedures for industrial applications

• Possible reduced performance of the electric insulating materials.

– Such as existing IGBT silicon gel facing various external insulation liquids.

– Systematical studies on silicon gel in contact with insulation liquid candidates.

• Impact from humidity on the power semiconductor insulation

– Giving requirements to the surrounding filling liquid, or to barriers between the most critical locations and external less critical filling liquid.

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Base plate / Heat sink

E1 C1 E2 Diode D2 Transistor T1

Plastic housing / Hard cover

Gel


Coating for chip protection (orange)




Gel

New top coating (blue)

Options for enabling PT planar/ bonded IGBT modules

Requirements:

• Provide 100% filling of solids or liquids

• Electrical insulation properties as good as or better than existing/replacement materials

• The required long term chemical compatibility between the new materials and with the existing component interface materials (e.g. with existing gel of IGBT modules, or with chip surface if gel is not used).

• Sealing properties (particles, ions, humidity) as good as or better than existing/replacement materials.


Investigering the most critical locations of the semiconductor chips

Guard rings for controlling E- field

Vce

1200V,400m

• Dedicated insulation material experiments

– On IGBT & diode chips

– On substrates

– Complete modules

– Long term insulation stress

– Controlled humidity

– Material compatibility

• Live experiments with converter modules

– Alternative insulation schemes

– In switch mode operation

– Up to rated component voltage of 6.5 kV


Some PP-film capacitor challenges

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Assumed interior weak points of metallized film capacitor

Risk for unsuccessful self-healing under high pressure


• Planar bonded IGBT modules

• Highest voltage available (6.5kV)

• Press-pack IGBT

• Highest voltage available (4.5kV)

• Need 100% filling of dielectric liquid

• Good electric insulator

• Free from contaminants

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Power semiconductor test objects

GateEmitter

Collector


IGBT driver electronics test object

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SINTEF driver interface board

Signal (Opt)

Power

Concept1SC0450V driver

Pressure vessel

External signalling

External power


Capacitor test objects

• PP-film capacitor elements for live testing

• PP- films 4µm, 5.8µm, 8.5µm, 9.8µm

– for self-healing experiments

– for liquid compatibility experiments

• Ceramic capacitor test samples for live testing

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Test cell for experiments with live converter module in liquid pressurized environment

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Major HSE concerns:• High voltage• High current• High pressureSolved by:• Custom test circuits• Certified pressure vessels• Multiple safety barriers


Test circuit for experiments with live converter modules in liquid pressurized environment 0-300 bar

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Solving HSE concerns:• Separate voltage supplies for continuous operation and

insulation testing High impedance line supply Very high impedance insulation tester

• Circulating power• Limiting external DC buffer capacitor• Limiting capacitor test object in pressure vessel• Pressure vessel certified to 500 bar• 100% liquid filling• Multiple safety barriers

• Pulse testing

• Continuous switching

• Voltage withstand ability testing

3 3

IGBT

driver

IGBT

driver

IGBT

driver

Variac3

3

400 V

supply

High voltageHigh

impedance source

+

-

IGBT

driverRS

Pressure vessel


Live experiments of capacitors in pressurized environment

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C1 C2

Pressure vessel

V V

UDC

UDC

V

A

A

VDC,inv

A

T

T

T

AC

DC

Troom

Ttank

Tcap

T T liquidH

P

Icap

VDC,cap

+

-

10

:6

Lfilt

ptank

• Characterization: IEC 61071:2007

• Voltage: Up to 1.5x rated DC

• Current: Up to rated AC

• Test liquid: Midel@7131

• Pressure: 0-300 bar

Solving HSE concerns:• Separate voltage and current control• High impedance voltage source• Resonant mode current control• Pressure vessel certified to 500 bar• 100% liquid filling• Multiple safety barriers


Insulation material experiments

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Materials – Liquids1. Midel – Synthetic ester2. FR3 – Organic ester3. Fluorinert FC-77(3M)4. Perfluorpolyether – Galden (Solvay)5. Monobenzyltoluene - Jarylec

Test objects• Custom made PCB• 6.5 kV DBC substrate• 4.5 kV diode chips• 6.5kV IGBT modules

Materials – surface cover1. Parylene2. Silicone Gels3. Polyimide

Conditions

• Influence of water

• Influence of temperature


Chip termination area is vulnerable for particles

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4.5kV diodeTest object

Microscopy analysis after insulation breakdown


Findings from live experiment with converter module 0-300bar

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Pressuretest

program

VIGBT

IIGBT

VFWD

IFWD

Measuring Turn ON/OFF

time

time

time

time

1 sec

max ~160 usec

1 sec

"Double pulsing" waveforms


Some findings from live experiments of PP film capacitors

• 0-300 bar in synthetic ester Midel 7131

• Failures have been experienced

– When subject to 1.5 times rated DC voltage

– Own post investigations and by the manufacturers gives reason to suspect unsuccessful "self-healing"

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Close to failure(several layerspenetrated)

Complete failure

Several successfulevents


Interim conclusions capacitors

• PP-film capacitors and ceramic capacitors

– All electrical characteristics, such as capacitance and tan δ are well maintained in high pressure liquid environment up to 300 bar.

– The mechanical durability such as the film interconnection to the termination layers is maintained.

• PP-film capacitors

– Even though traces from the surrounding liquid are found inside the film roll, there are no indications of deterioration of the film metallization like erosion.

– The major concern is that the important self-healing mechanism of the metalized PP-film seems to be negatively affected by the high pressure.

– Continuing experiments applying reduced DC-voltage has been in operation for a significant longer period compared to those resulting in failure.

– This is taken as an indication that high pressure operability of PP-film capacitors could be feasible provided significant derating of operating voltage

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Interim conclusions IGBT and IGBT driver packaging

• All electrical characteristics as well as mechanical ruggedness are maintained at least up to 300 bar– IGBT voltage and current waveforms close to unaffected by pressure

– Indicating that IGBT and IGBT driver electrical functionality have the sufficient pressure ruggedness

• Chip termination area is vulnerable for fibers and other particles.– The chip and substrate interface need to be protected from direct contact with liquids by a

material with the sufficient mechanical and electrical properties.

– One option is to maintain the generally used silicon gel, however the long-term compatibility with adjacent liquids need to be further investigated

– Experiments with 30-50µm Parylene covering the silicon die surface look promising

– Long-term compatibility between liquids and adjacent IGBT materials to be further investigated

• Humidity control is important– By time humidity will penetrate the complete converter environment, including critical

locations

– Then either hermetically sealed components encapsulations are required

– Otherwise the complete converter filling liquid need to have humidity control

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Interim conclusions other components in 0-300 bar

• Magnetic core materials

– Iron wound cores, Amorphous wound cores, Ferrite cores, Nanoperm, Arnold powder cores

– Mapping coercive force, saturation flux density, relative permeability

– More or less affected by pressure

– All test objects seem to be possible candidates, provided proper design considerations

• Temperature and humidity sensors

– All have maintained their specified functionalities

• Current transducers

– Close to no influence from pressure on functionality, accuracy, characteristics

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-250 -200 -150 -100 -50 0 50 100 150 200 250-1.5

-1

-0.5

0

0.5

1

1.5

Ampere-turns N*I [At]

Magnetic f

lux B

[T

]

1 bar UP

300 bar

1 bar DOWN

1

2

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1: pressurized LEM2: Amorphous core (operated at 500 Hz)3: Nanocrystalline core(operated at 5000 Hz)4: Cable connectors(connected to penetrator)5: Close-up of LEM6: LEM capsule

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Thank you for your attention!

enabling pressure tolerant power electronics - …...1 findings and interim conclusions from 10...

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