Reduced Order Modeling for Cooling
-Battery/Electronics/Electric Machine Case Studies
Xiao Hu
Scott Stanton
ANSYS Inc.
1
© 2011 ANSYS, Inc.
September 25,
2014
Outline
 Motivation of using ROMs
 Introduction of LTI ROM
 LTI stands for linear and time invariant
 Advanced version of Foster network approach
 Introduction of SVD ROM
 SVD stands for singular value decomposition
 Coupling of ROMs with electrical circuit
models
2
© 2011 ANSYS, Inc.
September 25,
2014
Motivation of Reduced Order Model (ROM)
 CFD as a general thermal analysis
tool is accurate.
 Can be computationally expensive for large
models running transient CFD analysis
 ROM can significantly reduce the
model size and simulation time.
3
© 2011 ANSYS, Inc.
September 25,
2014
LTI ROM for Cooling
ICEPAK
1. Create the CFD model
2. Generate step responses
3. Generate the LTI ROM
 Use Simplorer
4. Simulate inside Simplorer
4
© 2011 ANSYS, Inc.
September 25,
2014
Example : An IGBT Model
 The IGBT device consists of 4 IGBT’s and 4 diodes.
 The device is cooled by cold plate below
5
© 2011 ANSYS, Inc.
September 25,
2014
Create the Step Responses in Icepak
 The number of CFD runs is equal to the number of
inputs (8 runs)
 The runs were done automatically using Icepak
6
© 2011 ANSYS, Inc.
September 25,
2014
IGBT Device Step Response

Step responses due to DIODE are shown below.

Both small and large time scale exist.

Self-heating is much larger than cross-heat.

The DIODE has strong impact on IGBT_A , but not much on IGBT_A.3

Only one of the eight sets of impulse responses are shown.

7
There are 64 step responses in total.
© 2011 ANSYS, Inc.
September 25,
2014
Create the LTI ROM in Simplorer
 In simplorer ROM model is created based on the step
responses.
8 inputs (power dissipation) and 8
outputs (temperature)
8
© 2011 ANSYS, Inc.
September 25,
2014
LTI ROM vs CFD Results
 To validate the LTI ROM results, same heat profiles
are used in both LTI ROM and CFD and then results
compared.
Sample heat
profile
Similar profiles were givens as inputs to
all IGBT’s and Diodes
9
© 2011 ANSYS, Inc.
September 25,
2014
LTI ROM vs CFD Results
10
© 2011 ANSYS, Inc.
September 25,
2014
LTI ROM vs CFD Results
11
© 2011 ANSYS, Inc.
September 25,
2014
LTI ROM vs CFD Run-Time
CFD runs in 2 hours
12
© 2011 ANSYS, Inc.
September 25,
2014
LTI ROM runs in less than 2 seconds.
Example : A GM Battery Module
 The module consists of 16 cells.
 Hybrid mesh with a mesh count
of 3 million.
13
© 2011 ANSYS, Inc.
September 25,
2014
LTI ROM for GM Battery Module
Heat Profile
LTI ROM gives the same results as CFD. LTI
ROM runs in less than 2 seconds while
the CFD runs 2 hours on one single CPU.
X. Hu, S. Lin, S. Stanton, W. Lian, “A Foster Network Thermal Model for HEV/EV Battery Modeling,” IEEE TRANSACTIONS ON
INDUSTRY
VOL. 47, NO.September
4, JULY/AUGUST
14
©APPLICATIONS,
2011 ANSYS, Inc.
25, 2011
X. Hu, S. Lin, S. Stanton, W. Lian, “A State
Space
Thermal
Model for HEV/EV Battery Modeling", SAE 2011-01-1364
2014
Icepak Model of the Cooling System
 Cold plate liquid cooling system :
15
Simplified cold plate without streams fluid design,
Glycol solution at 70°C,
Forced convection environment at 70°C.
© 2011 ANSYS, Inc.
September 25,
2014
Icepak-Simplorer LTI ROM
 Import Icepak model into
Simplorer
 Computation and creation
of the ROM from all the
.out files generated by
Icepak analysis
 New wizard helping on the
setup and configuration of
the LTI ROM creation
 Comparison of the
transient response of the
3D model and the 1D LTI
ROM
16
© 2011 ANSYS, Inc.
September 25,
2014
Meet the SVD ROM
 The LTI ROM can give temperature solution at user
specified locations, but not temperature fields.
 SVD ROM technology allows for quick temperature field
calculation in addition to average temperature
calculation.
VS
S. Asgari, X. Hu, M. Tsuk, S. Kaushik, “Application of POD plus LTI ROM to Battery Thermal Modeling: SISO Case,” SAE congress 2014.
X.17
Hu, S. Asgari,
Stanton, C-CSeptember
Hsu, Z. Shi,25,
B. Wang, H-K Chu, “A Transient Reduced Order Model for Battery Thermal Management Based
© 2011I. Yavuz,
ANSYS,S.Inc.
on Singular Value Decomposition,“ ECCE
2014.
2014
Animation is a Trajectory
18
© 2011 ANSYS, Inc.
September 25,
2014
SVD ROM for Cooling
1.
2.
Create the CFD model
Generate step responses
 Cannot use Icepak
 Can only use FLUENT
3. Extract SVD ROM
 Use Simplorer
4. Simulate inside Simplorer
5.
Post-process results in Fluent
ANSYS Fluent
19
© 2011 ANSYS, Inc.
September 25,
2014
ANSYS Fluent
SVD ROM : An IGBT Model
 Convective cooling channels used.
 Four IGBTs and four diodes generating heat.
 Icepak is used to create the mesh.
 Fluent model is exported from Icepak.
 Mesh size : 900 K.
20
© 2011 ANSYS, Inc.
September 25,
2014
SVD ROM vs. Fluent CFD
 To validate the SVD ROM results, same heat profiles
are used in both SVD ROM and CFD and then results
compared.
Similar profiles were givens as inputs to
all IGBT’s and Diodes
21
© 2011 ANSYS, Inc.
September 25,
2014
SVD ROM vs. Fluent CFD
CFD (15 sec)
CFD (30 sec)
CFD (45 sec)
CFD (60 sec)
SVD ROM
(15 sec)
SVD ROM
(30 sec)
SVD ROM
(45 sec)
SVD ROM
(60 sec)
While the two sets of results look very similar,
the SVD ROM runs orders of magnitude faster!
22
© 2011 ANSYS, Inc.
September 25,
2014
Animation from SVD ROM
Such an animation takes about 10 min to create!
23
© 2011 ANSYS, Inc.
September 25,
2014
SVD ROM Validation: GM 16 Cell Test Case
CFD (200 sec)
CFD (400 sec)
CFD (600 sec)
CFD (800 sec)
SVD ROM
(200 sec)
SVD ROM
(400 sec)
SVD ROM
(600 sec)
SVD ROM
(800 sec)
X.24
Hu, S. Asgari,
Stanton, C-CSeptember
Hsu, Z. Shi,25,
B. Wang, H-K Chu, “A Transient Reduced Order Model for Battery Thermal Management Based
© 2011I. Yavuz,
ANSYS,S.Inc.
on Singular Value Decomposition,“ ECCE
2014.
2014
Temperature Distribution - Animation
Temperature calculated from CFD.
5 hr simulation time with 6 CPUs.
Temperature calculated from SVD ROM.
0.5 hr simulation time with 1 CPU.
X.25
Hu, S. Asgari,
Stanton, C-CSeptember
Hsu, Z. Shi,25,
B. Wang, H-K Chu, “A Transient Reduced Order Model for Battery Thermal Management Based
© 2011I. Yavuz,
ANSYS,S.Inc.
on Singular Value Decomposition,“ ECCE
2014.
2014
SVD ROM Validation
26
CFD (10 sec)
CFD (20 sec)
CFD (30 sec)
CFD (40 sec)
SVD ROM
(10 sec)
SVD ROM
(20 sec)
SVD ROM
(30 sec)
SVD ROM
(40 sec)
© 2011 ANSYS, Inc.
September 25,
2014
SVD ROM Validation: Prius Motor
CFD (200 sec)
CFD (400 sec)
CFD (600 sec)
CFD (800 sec)
SVD ROM
(200 sec)
SVD ROM
(400 sec)
SVD ROM
(600 sec)
SVD ROM
(800 sec)
27
© 2011 ANSYS, Inc.
September 25,
X. Hu, S. Lin, S. Stanton, “A Transient Reduced
2014 Order Model for Electric Machines Based on Singular Value Decomposition,“ ITEC 2014.
GM Battery Module – ECM Coupled with ROMs
 ECM calculates heat source and sends it to the two ROMs.
 LTI ROM calculates average temperature and sends it to ECM.
 SVD ROM calculates temperature distribution.
28
© 2011 ANSYS, Inc.
September 25,
2014
ROMs/ECM Coupled Results

LTI ROM calculates average temperature.

SVD ROM calculates temperature field.
 Needs to be post-processed back in FLUENT.

ECM calculates electrical performance.
Average Cell Temperature
29
© 2011 ANSYS, Inc.
September 25,
2014
Battery Voltage as a Function of Time
Complete Drive System Simulation
3-phase currents (left) and junction temperature of IGBTs and diodes (right).
30
© 2011 ANSYS, Inc.
September 25,
2014
Conclusion
LTI ROM has shown to give similar results as
CFD but runs orders of magnitude faster.
SVD ROM helps calculate temperature field,
which gives more information than LTI ROM.
Both ROMs can be used in conjunction with
electrical circuit models to have two-way
coupled simulation.
31
© 2011 ANSYS, Inc.
September 25,
2014
Q&A
Xiao Hu
734-213-1261
[email protected]
32
© 2011 ANSYS, Inc.
September 25,
2014