Lifetime prediction of high-power press-pack IGBTs
in wind power applications
PhD student: Cristian Busca
Email: cbu@et.aau.dk
Aalborg University, Department of Energy Technology, Denmark
Vestas Power Program
AAU supervisors: Remus Teodorescu, Frede Blaabjerg
Vestas reference group: Lars Helle, Tusitha
Abeyasekera, Philip Carne Kjær
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25 November 2013
Outline
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•
•
•
•
•
•
•
2
Background and motivation
Project objective and modelling frameworks
Description of the studied PP IGBT
Power loss and thermal modelling of PP IGBTs
Lifetime prediction of PP IGBTs
Contributions, future work and list of publications
References
Acknowledgement
25 November 2013
Background and motivation (1)
•
•
•
Growth in the size of wind turbines over time [1]
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The next generation large WTs are
likely to be larger than todays WTs;
The next generation large WTs should
have high reliability;
According to the 2009 renewable
energy directive the installed wind
power capacity should be significantly
increased by the year 2020 [1];
Background and motivation (2)
•
•
•
Comparison of wind turbine subassembly failure rates [2]
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25 November 2013
The grid/electrical system achieve
the highest failure rates;
The rotor/blades and the electrical
control (power converter) also
have notable failure rates;
The power converter is a critical
subassembly of a WT;
Background and motivation (3)
Wire-bonded IGBT
PP IGBTs offer the following advantages:
• high-power capability;
• high power density (double-side cooling);
• high thermal cycling capability;
• easy series connection (stacking);
• short-circuit failure mode;
PP IGBTs eliminate the reliability bottlenecks found in Al
wire-bonded IGBTs:
• bond wires;
• Solder joint under the chip;
• Solder joint under the substrate;
PP IGBT (42 chips)
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Background and motivation (4)
PP IGBTs require:
• proper mechanical clamping (achieved with a
mechanical clamp);
• proper cleaning of the contacting interfaces prior to
assembly;
• the use of thermally and electrically conductive
grease on the contacting interfaces;
• proper assembly of the components in the stack;
• de-ionized water cooling system if Al cooling plates
are used;
• tap water cooling system if AlN cooling plates are
used;
Stack with 2 PP IGBTs and 3 cooling
plates
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Project objective
Investigate how mechanical clamping conditions and manufacturing
tolerances affect the lifetime of PP IGBTs in wind power applications.
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Modelling frameworks (1)
Proposed framework for the development of clamping force dependent thermal impedances
Proposed framework for the circuit simulator implementation
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Modelling frameworks (2)
Framework for the lifetime prediction
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Description of the studied PP IGBT (1)
a)
b)
c)
d)
e)
f)
Components of an IGBT chip assembly
The components are:
a) Collector side Mo plate (helps with contact pressure distribution);
b) Si chip;
c) Emitter side Mo plate (helps with contact pressure distribution);
d) Shim plate (holds the plastic housing);
e) Gate sprung pin
f) Plastic housing
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Description of the studied PP IGBT (2)
Clamping force
C_pole
C_Mo_plate
C_pole to C_Mo plate
Si chip
C_Mo plate to Si chip
E_Mo_plate
Si chip to E_Mo plate
Shim plate
E_Mo plate to shim
Pedestal
Shim to pedestal
E_pole
Clamping force
Heat spreading effect
Definition of the components and contacts for the open-capsule
PP IGBT
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25 November 2013
The clamping force influences:
• Thermal contact resistance;
• Electrical contact resistance;
• Thermal cycling capability;
• Short-circuit current rating;
Power loss modelling (1)
chip-level conduction loss data
6
25 C
125 C
5
chip-level turn-off loss data
0.25
0.2
1 kV
2 kV
2.8 kV
0.15
E [J]
Vce [V]
4
3
0.1
2
0.05
1
0
0
20
40
60
Ic [A]
80
100
120
0
20
140
•
1 kV
2 kV
2.8 kV
0.4
•
E [J]
0.3
0.2
35
40
Ic [A]
45
50
55
60
The power loss data is based on look-up
tables;
The chip-level loss data has been
estimated from the component-level
loss data;
0.1
12
30
chip-level turn-on energy loss data
0.5
0
20
25
25
30
35
40
Ic [A]
45
50
55
60
25 November 2013
Power loss modelling (2)
Collector pole
•
Si chip - 1
Si chip - 9
Rel - cont - 1
Rel - cont - 9
Rel - mat - 1
Rel - mat - 9
Lstray - 1
Lstray - 9
•
•
•
The IGBTs have a temperature and
current dependent on-state resistance;
Rel-cont is given by the electrical contact
resistances;
Rel-mat is given by the material electrical
resistances;
Lstray is given by the commutation path
stray inductance;
Emitter pole
Simplified chip-level electrical network of
the open-capsule PP IGBT
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Thermal modelling of PP IGBTs (1)
No.
Material
Thermal
Thermal
Density
conductivity
capacity
[kg/m3]
[W/(m*K)]
[J/(kg*K)]
1
Si
148
741
2330
2
Mo
145
217
10200
3
Ag
407
234
10500
4
Cu
394
381
8930
The thermal models are developed based
on:
• geometric parameters of the opencapsule PP IGBT;
• material properties;
• interface specific thermal contact
constants;
• chip-level clamping forces;
The thermal model takes into account very
well the heat spreading effect and thermal
coupling between the chips.
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Lifetime prediction (1)
Current and temperature feedback
MP (power
vs time)
Control
signals
Matlab/
Simulink
Plecs
Chip-level
temperatures
Circuit simulator implementation framework
•
•
leg1
leg2
IGBT1
IGBT3
D1
Vdc
D3
Load
+
IGBT2
IGBT4
D2
D4
Control
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25 November 2013
•
•
a 2-level power converter has
been considered;
grid connection has been
emulated;
output frequency: 50 Hz;
switching frequency: 1.5 kHz;
Contributions
•
Development of a clamping force distribution model for the open-capsule PP IGBT and
investigation on the clamping force distribution among the chips under various mechanical
clamping conditions;
•
Development of chip-level thermal models for the open-capsule PP IGBT and investigation
on the effect of mechanical clamping conditions on the chip-level thermal impedances;
•
Investigation on the effect of mechanical clamping conditions on the chip-level thermal
cycling and lifetime of PP IGBTs in WT like applications (using realistic mission profiles) by
means of circuit simulator implementation;
•
Design and construction of a test setup for PP IGBTs in order to validate to some extent the
developed models (clamping pressure, chip current and chip temperature measurements);
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Future work (1)
Clamping force distribution modelling
• Include the effect of temperature in the model (couple it with a thermal model);
Power loss modelling
• Determine the chip-level power loss data experimentally (from 25 ⁰C to 125 ⁰ C);
Thermal modelling
• Use temperature dependent material properties in the thermal model;
• Use clamping force and temperature dependent thermal contact coefficients;
• Apply the power loss in the center area of the Si chips;
Circuit simulator implementation
• Model the temperature dependent on-state characteristics of the Si chips in a better way
by considering the effect of both temperature and current;
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Future work (2)
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•
•
Do not consider the switching transients in the circuit simulator implementation in order to
speed up the simulation (longer mission profiles);
Include the effect of force dependent electrical contact resistances in the model;
Use physics of failure lifetime model instead of the exponential model;
Experimental part
• Use de-ionized water cooling system in order to be able to carry out tests under realistic
operating conditions;
• Measure the current, contact pressure and temperature distributions under non-ideal
clamping conditions;
• Use miniature strain gauges in order to measure online the chip-level clamping forces;
• Carry out thermal cycling tests at various clamping forces;
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25 November 2013
List of publications (1)
Journal papers:
[jp1] C. Busca, R. Teodorescu, F. Blaabjerg, S. Munk-Nielsen, L. Helle, T. Abeyasekera, P. Rodriguez, “An overview
of the reliability prediction related aspects of high power IGBTs in wind power applications”, in proc. of the 22nd
ESREF, Microelectronics reliability (Elsevier journal), vol. 51, issues 9-11, pp. 1903-1907, September-November
2011 (the paper is available on www.sciencedirect.com).
[jp2] A. A. Hasmasan, C. Busca, R. Teodorescu, L. Helle, F. Blaabjerg, “Electro-thermo-mechanical analysis of
high power press-pack IGBTs under non-ideal mechanical clamping conditions”, IEEJ journal of industry
applications, 2013 (the paper has to be re-submitted after minor review).
Conference papers:
[cp1] C. Busca, R. Teodorescu, F. Blaabjerg, S. Munk-Nielsen, P. Rodriguez, L. Helle, T. Abeyasekera, M. Sztykiel,
“Press-pack IGBTs: a reliable solution for medium voltage multi-MW wind turbine power converters”, in proc. of
10th international workshop on large-scale integration of wind power into power systems as well as on
transmission networks for offshore wind power plants, Aarhus, Denmark, October 2011.
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List of publications (2)
[cp2] A. Hasmasan, C. Busca, R. Teodorescu, L. Helle, “Modelling the clamping force distribution among chips in
press-pack IGBTs using the finite element method”, in proc. of 3rd IEEE international symposium on PEDG, pp.
788-793, June 2012.
[cp3] C. Busca, R. Teodorescu, F. Blaabjerg, L. Helle, T. Abeyasekera, “Dynamic thermal modelling and analysis of
press-pack IGBTs both at component-level and chip-level”, in proc. of 39th annual conference of the IEEE
industrial electronics society on IECON, November 2013 (the paper was accepted for presentation).
[cp4] M. Sztykiel, R. Teodorescu, S. Munk-Nielsen, C. Busca “Losses analysis of different grounding schemes for
transformer-less wind turbine with full-scale power converter”, in proc. of 12th international workshop on largescale integration of wind power into power systems as well as on transmission networks for offshore wind
power plants, London, United Kingdom, October 2013 (the paper was accepted for presentation).
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References
[1] EWEA, “Wind energy factsheets, EWEA 2010”, (available at: www.ewea.org);
[2] P. J. Tavner, F. Spinato, G.J.W. van Bussel, E. Koutoulakos “Reliability of different wind turbine concepts with
relevance to offshore application”, European Wind Energy Conference, Brussels, 2008;
[3] http://www.fujifilm.com/products/prescale/prescalefilm/
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Acknowledgement
Supervisors: Remus Teodorescu, Frede Blaabjerg, Pedro Rodriguez (from Sep. 2010 till Sep.
2011);
Vestas reference group: Lars Helle, Tusitha Abeyasekera, Philip Carne Kjaer;
IXYS WESTCODE UK: Frank Wakeman, Ashley Golland, Howard Neal, Stephen Reynolds, Julian
Pitman, Gangru Li;
Stig Munk-Nielsen;
All my colleagues in the Vestas Power Program and at the Department of Energy Technology;
The staff of the Department of Energy Tehcnology and Doctoral School of Engineering;
The Phd project has been supported by the Vestas Power Program (Aalborg University – Vestas
wind systems partnership);
The Phd project has been also supported by CORPE (Centre of reliable power electronics), for a
period of 3 months;
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Thank you for your attention.
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25 November 2013