Simulation of IGBT converter - Model Order Reduction

Simulation of IGBT converter
E. Rudnyi
CADFEM GmbH
erudnyi@cadfem.de

Outline
The work has been done for the ECPE workshop Thermal
Engineering of Power Electronics Systems, 2009
Overview
Thermal Simulation in Icepak
Compact Thermal Model through Model Order Reduction
1

European Center for Power Electronics
2

IGBT Converter
Insulated Gate Bipolar Transistor:
Very efficient – thermal losses about just 5%
However 20 kW converter produces 1 kW power dissipation.
Electrothermal simulation is required:
3
Electrical properties of IGBT depends on temperature;
Too high temperatures reduces reliability and durability.
T j
T c

The Model of the Converter
4
Original Model
Model in Icepak
Model in Icepro

Simplifying the Heat sink In Icepro
5

Power dissipation, materials, boundary conditions
6

Mesh
7

Solution - convergence
8

Typical Simulation Results
9

Comparison with Experimental Measurements
10
80
70
60
50
40
30
20
10
0
trial1 trial2 trial3 trial4
T1ex
T1sim
T2ex
T2sim
Tref_ex
Tref_sim

Transient Simulation in Icepak
Flow is developed: We need to
solve only energy equation.
11

From Finite Elements to System Simulation
12
Physics &
Geometry
System of
FEM MOR
n ODEs
Electrothermal Simulation with IGBTs:
From ANSYS Workbench to System Level
Reduced
System of
r

Model Order Reduction
Relatively new technology
Solid mathematical background:
13
Approximation of large scale
dynamic systems
Dynamic simulation:
Harmonic or transient simulation
Industry application level:
Linear dynamic systems

Model Reduction as Projection
Projection onto lowdimensional
subspace
14
x Vz
x = V
z
E
How to find
subspace?
Mode
superposition is
not the best way
to do it.
V
T
Ex Kx
Bu
T
T
EVz
V
KVz
V
Bu
E r

Transferring Model from Icepak to Workbench
15
Q
hA
( T Tbulk
)

MOR for ANSYS: http://ModelReduction.com
16
Workbench
ANSYS Model
FULL files
Mx
Ex
Kx
y Cx
Bu
Linear Dynamic
System, ODEs
Current version 2.5
Simulink,
Simplorer, VerilogA,
…
Small dimensional
matrices
MOR Algorithm

Model Reduction: Inputs and Outputs
12 inputs and outputs have been defined
17

Model reduction
Dimension of the model in ANSYS is about 900 K DoFs.
Dimension of the reduced model is 15 DoFs per input = 15*12 = 180.
The reduced model covers all heat sources and thermal cross talk at
once.
Transient simulation when 1 W has been applied only on device.
Step response.
On the next slides there is comparison between the simulation of the
full model in ANSYS and the reduced model for T_A1. This curve
corresponds to thermal impedance.
18

Comparison
Red line – ANSYS, green line – reduced model. Difference is close to
the line thickness. For such accuracy, one needs 15 DoFs per input.
19

Comparison
Relative error between results in ANSYS and reduced model.
20

Comparison with Measurements
Cooling curves from the stationary state with:
75 W on IGBTs
0 W on diodes
T ambient = 28.5
Using point T2 (P2) and the average on the upper face of IGBT T_B2
for comparison with the measurements
21

Temperatures on IGBTs
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Temperatures under IGBTs
23

Simulation in Simplorer
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E1
z_up
P1
P2
P3
P4
z_vp
Ambient
P_ REF
Q
P5
P6
P7
P8
z_wp
z_um z_vm z_wm
P1 2
P1 1
P1 0
P9
Thermal Domain
Electrical Domain
VM311 R6 R5 R4
+
V
IN_A
IN_B
IN_C
U2
Simplorer4
A
A
A
OUT_A
OUT_B
OUT_C
R1 R2 R3
A
B
C
Induction_Motor_20kW
N
ROT1
ROT2
Mechanical
Domain
0
MASS_ROT1

Conclusion
Icepak to quickly simulation IGBT converter
Compact dynamic thermal model are necessary
Transfer to ANSYS Workbench with convection boundary conditions
Compact thermal model are obtained through model reduction
25