reliability of power electronic converters for offshore wind … · 2014. 11. 17. · 2l-vcs (one...

Technology for a better society

Magnar Hernes SINTEF Energy Research

[email protected]

1

A main topic in the research project:

"Power Electronics for Reliable and Energy Efficient Renewable Energy Systems"

Short name: OPE

Duration: 2009-2014

Financing: The Research Council of Norway and three industry partners

Web: www.sintef.no/OPE

Reliability of power electronic converters for offshore wind turbines

http://www.sintef.no/OPE

Technology for a better society 2

Control strategies for grid connected converters

Topic

Energy efficient electrical conversion and transmission

Topic

Analysis and fault handling of advanced hybrid AC/DC grids

Topic

Reliable power electronics for renewable energy systems

Topic

Scenario analysis

Laboratory experiments & verifications

Reliable and Energy Efficient Renewable Energy Systems

New models for numerical simulation

Topic


Tr D

DTr

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DTr

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DTr

V

W

U

D

2

1

DC-link

2L-VCS = 2-level Voltage Source Converter

3

Power electronics for wind farm power conversion

HVDC HV MV

privat forbruk

B2B-VSC

B2B-VSC

IGBT = Insulated Gate Bipolar Transistor


Submodule #1

Submodule #2

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[H]

[H]

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[H]

[H]

Submodule #1

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Vdc

Modular Multilevel Converter - MMC

4

Converter topologies for MV and HV applications

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DTr

Vdc_Sub

IGBT_1

IGBT_2

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DTr

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DTr

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DTr

V

W

U

D

2

1

DC-link

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1

U phaseVdc

2L-VCS (one phase-leg)

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Series connection of IGBTs

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D

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2

Vdc/2

U phase

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D

D

DVdc/2

1

Neutralpoint

3L-VCS (one phase-leg)

Due to voltage limitation of single IGBTs, MV and HV converters need more complex topologies and/ or series connection of IGBTs

Test objects for reliability

investigations


Reliability of power semiconductors - Failure modes

• Spontaneous failures due to overloads – Related to power semiconductor chips

– Thermal overload and overvoltage

– Exceeding V/I safe operating area for the device

• Failures triggered by external environment – E.g. intrusion of humidity

– E.g. cosmic radiation

• Failures due to aging or exhaustion – Mechanical and electrical termination of

the chips

– Packaging and encapsulation

5

Woff = ∫ Poff (t)dt

Poff (t) = v(t) x i(t)

Transistor current i(t) Transistor voltage v(t)

Several MW on a few square centimetre chip

Typical turn-off behaviour for a controllable power semiconductor

• Mostly chip related: – Spontaneous failures – Cosmic radiation

• Mostly related to packaging – Ageing or exhaustion – Intrusion of humidity in chip insulation

Project focus


IGBT packaging

• Mainly two technologies – Planar bonded modules

– Press-pack housing

• Both can contain both IGBT chips and antiparallel free-wheeling diodes

6

• A 750A/ 6500V IGBT module from Infineon

• An 1800A/ 4500V press-pack IGBT from Westcode


Planar bonded IGBT modules • Main failure mechanisms:

– Bond wire lift off

– Solder layer disconnect

• Thorough investigations and publications of failure mechanisms and reliability

• Failure mode Failure to break

7

chip Cu

Ceramic

Cu base plate

Heat sink

Weak point: Chip solder

Weak point: Bond connection

Bond wire

Weak point: Solder connection to base plate

Direct Bonded Copper - DBC Cu

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Consequence:

Valve failure

Converter failure


Life time curves – no of cycles to failure

• ∆T • Tmax

• dT/dt • ton

• ILoad

• control strategy • and more….

Experience data from modules: Lifetime dependent on:


Press-pack IGBTs

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• Failure mechanisms: – Limited knowledge

• Few publications on failure mechanisms and reliability

• Failure mode Expected failure to short

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Consequence:

Valve still functional

Reduced voltage margins to failure


Main focus on reliability of press-pack IGBTs in the OPE project

• The OPE project prioritized reliability of press pack devices for the following reasons: – Limited published information regarding failure mechanisms and power cycling life time

– Press-pack devices are very relevant in medium voltage wind power applications due to series connection capabilities (fail-to short-circuit)

– Special power cycling stress condition for wind power converters (wind fluctuations, low motor side frequency etc.)

• Then we need to know: – Load profiles for the application, e.g. power cycling due to wind fluctuations

– Stress levels related to grid side and generator side load conditions (power frequency, cos ϕ etc.)

– Stress levels related to the converter power circuit and controls (topology, switching frequency etc)

• Theoretical work

• Experimental work

10


GEN GRID

3L NPC VSC 3L NPC VSC

• DC link voltage ~ 5 kV

• 3.3 kVac (LL voltage)

• Switching frequency ~ 1500 Hz +/-

• 5 MVA (connected to a 3.6 MW wind turbine gen.)

• IGBT: Press-pack1800 A/4500 V

Case study: A medium voltage PWM 3L-NPC VSC for 3.3 kV AC


Test Cell for mapping switching characteristics of HV IGBTs

• Present Test Cell with 0-5 kV DC-link

• Planned to be extended to 10kV

• "Double-pulse" waveform for measuring IGT turn-on and turn off waveform

• External liquid (silicon oil) heating/cooling circuit for temperature control (5- 50 oC)

V IGBT

I IGBT

V FWD

I FWD

Measuring Turn ON / OFF

time

time

time

time

1 sec

max ~ 160 usec

1 sec


Turn-off waveforms with DC-link 2800V and turn-off current 1800A

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Test object: 1800A/4500V press-pack IGBT

~3500V

~1800A

~6MW

Psw_off =7Joule x 1000Hz =7kW

Ptotal=Psw_off+Psw_on+Pcond


Power Cycling Tester for life-time testing of high-power IGBTs (2000 A)

Project investment of ~1MNOK. Developed in cooperation with Chemnitz University of Technology


Operation of the Power Cycling Tester

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a1: Measure VCE cold a2: Measure Tcase cold

Temperaturestime

time

Tvj,max

Tvj,minTcase,min

Tcase,max

∆Tvj

Current through IGBT

Tvj

Tcase

Iload0-2000A

Load current on (heating period)

da

bc

ton toff

1 cycle

Load current off (cooling period)

b1: Measure VCE warm b2: Measure Tcase warm

c1: Measure VCE warm Estimate Tvj,warm

d1: Measure VCE cold Estimate Tvj,cold

1-4 IGBT test pairs Bypass leg

Cur

rent

Sou

rce

I LOAD

0

-200

0AV L

OAD

0

-20V


OPE Power Cycling Tester – Control screen

Continuously sensed parameters Stored parameters of the last cycle

Trend analysis of the stored parameters


Plot from measurement of planar bonded modules

Indicating fatigue of chip solder

Indicating bond wire lift off

From Chemnitz University of Technology


Power Cycling Tester with 4x modules + 4x press packs


Modelling press-pack IGBT for stress analysis Work by PhD student Tilo Poller at Chemnitz University of Technology


Simulation model of (PSCAD) of PWM Voltage Source Converter

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g_Rp

g_Rm

g_Sp

g_Sm

g_Tp

g_Tm

g_Sp

g_Tp

g_Tm

g_Sm

g_Rp

I_T

I_S

I_T

I_S

0.0014

0.0014

I_R

I_S

I_T0.0014

VT

*1E3

DC-link Active front end PWM converter

VR

Load / Source

g_Rm

123

Scale factor (from kA to per unit (pu))(1.0 pu = 28 A = 0.028kA)Note: Peak values !

0.053

0.053

A

B

C

A

B

C

66.0

I_mains_R

I_mains_S

I_mains_T

2T3

2T6

2T5

2T2

D3 D5

D4 D6 D2

I_mains_T

I_C

_R

I_C

_T

*

I_DC

V_DC

V_DC

V_DC

I_DC *1E3

P_DC

66.0

I_C_R

66.0

0.00

1

0.00

1

I_DC

I_R

I_PWM

I_PWM

I_PWM

ConverterDC_ref (kV)

0.1

0.9

0.45

I_react (pu)

-1

1

0

PWM controlOFF ON

1

IR Fund. rms

A rms0 0.04

0

VST

VRS

VRS

VTR

Pow

er AB

PQ

*2.5

I_R

Fault detectionShort cir. PWM

0 1

0

Power flowP

kW-10 10

-10

Q

kW-10 10

-10

MainsMains Volt

0.2

0.3

0.23

Frequency

40

60

50

Phase

-360

360

0

*25.2

*25.2

*25.2

2T4

VS

VT

LoadLoad (kA)

-0.05

0.05

0.001

V_DC

0 1

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P_DC

-20 20

-20

0.053

Active front end converterWed Dec 12 09:13:34 2001

ny_frontend_11FileDir J:\DOK\12\MO\Prosjekt\Sip 12X127\EMTDC\Frontend

2T1 D1

Short cir. PWM

I_R

0.0

0.0

| X |*1E3

Power calculation

0.02

0.02

6600

.066

00.0

V_DC_PVR

Short circuit detection

V_DC_P

0.0

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0.00

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VS

I_mains_S0.05

A

B

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VFPh

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VCC

_R

VCC

_S

VCC

_T

Filter Point of common connection

FFT-analysis

Result to fileWrite

-- Trigg

0

Store resultsOFF ON

0

V_R_0 V_R_G

V_DC

V_DC_N

V_R_G

V_R_0

Save result to file forMatlab analysis

V_R_0

V_R_G I_R

VCC_R

VRS

I_mains_R

I_mains_R

VR

In5

fileWrite Store

resulttrigger trigger

In4

In3

In2

In1

resultto file

In7

In6

lagreres.f

*2.5

VTR

VST

VRS

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Scale factor (from kV to per unit (pu))(1.0 pu = 400 V DC = 0.4kV)

Scale factor (from kV to per unit (pu))(1.0 pu = 230 V AC = 0.23kV)Note: Peak values

DCVoltage

Controller

I_ampVDC_ref

VDC_mea Generation of

I_ref

I_act

I_react

Theta

curr. references Current V_refI_ref

I_mea

Controller

g_Rp

g_Rm

g_Sp

g_Sm

g_Tp

g_Tm

On

PWM

V_ref

I_C

_S

Power Grid

FFT

In1

In2

In3

In4

In5

Plot

*3.074

*3.074

*3.074 Phase

loop (PLL)

VAC_mea Thetalocked


25 °C

125 °C

Curves or measurements

XDATA: x1 x2

YDATA: y1 y2 y3

ZDATA: x1y1 x1y2 x1y3 x1y1 x1y2 x1y3

ENDFILE:

Input file with loss data

Simulations

IGBT loss calculator in PSCAD with thermal network add-on


Simulated load dependent swings of IGBT hotspot temperature

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Motive:

• Combine laboratory measurements with numerical simulations to estimate efficiency and lifetime of power semiconductors

Simulated temperature swings affected by:

• Switching frequency

• Line-side and generator side power frequency, cos ϕ etc,

• Filter ripple current

• Wind fluctuations

• ..and more


Methodology for power cycling lifetime estimation

Step#1: Temperature determination Step#3: Lifetime prediction according

Miner’s rule

Step#2: Cycle counting

Possibility 1calculation

Possibility 2measurement

Tvj(t)

Minima and Maxima extraction

Input data:e.g.: P(t), Q(t),

wind speed

Ciruit simulationLosses model

Thermal model Rainflow counting algorithm

Linear composition

Nf curves

Residual lifetimexy%

Wind profile

Lifetime characteristics

Example: If not oversized lifetime for the generator side diode can be very short!


• Completion of the reliability work in the OPE project (deadline 30th June 2014)

• Continue power cycling of IGBTs

• Press-packs and modules

• Power Cycling of single chips (master student work)

• Post processing of result

• Final reporting and publications

• Develop a new research project for continuation of converter reliability topics

• Together with colleagues at Chemnitz University of Technology

• Start-up spring 2015

• Exploit results and ideas from OPE

• Address VSC converter applications for HV collecting and transmission systems

• Power cycling capabilities assuming various converter topologies and AC/DC systems

• New methods for condition monitoring, predicting rest life-time etc.

24

Planned continuing activities on converter reliability


Thank you for your attention !

reliability of power electronic converters for offshore wind … · 2014. 11. 17. · 2l-vcs (one...

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