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© 2011 ANSYS, Inc. September 29, 2011
1
Electromagnetic Force Coupling in Electric Machines
Mark Solveson, Cheta Rathod, Mike Hebbes, Gunjan Verma, Tushar SambharamANSYS, Inc.
© 2011 ANSYS, Inc. September 29, 2011
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Introduction
• Low noise regulation– Aimed at reduction in noise pollution
• Comfort Criteria– Noise causes discomfort and fatigue– Noise suppression demonstrates
technological/marketing edge
• Component Failure– Sensitivity of structure to acoustic resonances
• The above Applies to many Industry sectors:
– Transportation, Power, Environmental, Building services
© 2011 ANSYS, Inc. September 29, 2011
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• Noise and vibration in electric machines come from many sources.
• ANSYS provides excellent capabilities for the design and analysis of electric machines: – Electromagnetic performance– Electric Drive performance– Structural analysis– Thermal analysis– Acoustics analysis
• ANSYS field coupling technology allows mapping of electromagnetic forces for Mechanical analysis
Introduction
© 2011 ANSYS, Inc. September 29, 2011
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• Different machines may have different considerations depending on their architecture or control strategies.– Primary Forces are in-plane (radial and tangential)
• Single and Three Phase Induction Machines. • PM Synchronous Machines (Surface Mount, IPM).• Switched reluctance machines
– Primary force are Axial• Axial Flux Machines
Machine Types
© 2011 ANSYS, Inc. September 29, 2011
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Noise Sources [1]
Magnetic
Radial
Slot Harmonics
Magnetic Unbalance
Mechanical
Self
Stator
Modes of Vibration
Rotor
Bearings Balancing
Dynamic Eccentricity
Unbalanced Rotor
Elliptical Rotor Surface
Static Eccentricity
Auxiliaries Load Induced
Couplings
Foundation
Aerodynamic
Fluid Cooling Phenomena
Electronic
Switching Harmonics
[1] P. Vigayraghavan, R. Krishnan, “Noise in Electric Machines: A Review,” IEEE, 1998
Audible Frequencies
20 Hz 20 kHz5 kHz261.63 Hz60 Hz 4.186kHz
© 2011 ANSYS, Inc. September 29, 2011
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ANSYS Machine Model
© 2011 ANSYS, Inc. September 29, 2011
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• ANSYS Machine Design Methodology– RMxprt: calculate rated performance for machine– Maxwell: Calculate detailed magnetic FEA of machine in time
domain– Simplorer: Calculate detailed drive design with coupled
cosimulation with either RMxprt or Simplorer.
Electromagnetic Design and Analysis
© 2011 ANSYS, Inc. September 29, 2011
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Machine Model in Maxwell - Simplorer2D IPM (Interior Permanent Magnet) motor model created from RMxprt and Maxwell UDP (User Defined Primitive) for rotor
• 4 pole, 1500 RPM, 220 Volt DC bus.• Two Control Strategies used:
• 6 step inverter – In Maxwell• PWM current regulated – Cosimulation
Maxwell with Simplorer0
0
LPhaseA
LPhaseB
LPhaseC
2.00694ohmRA
2.00694ohmRB
2.00694ohmRC
0.000512893H*KleLA
0.000512893H*KleLB
0.000512893H*KleLC
LabelID=VIA
LabelID=VIB
LabelID=VIC
+ -11VLabelID=V14
+ -11VLabelID=V15
+ -11VLabelID=V16
+ -11VLabelID=V17
+ -11VLabelID=V18
+ -11VLabelID=V19
100ohmR20
100ohmR21
100ohmR22
100ohmR23
100ohmR24
100ohmR25
LabelID=IVc1 LabelID=IVc2 LabelID=IVc3 LabelID=IVc4 LabelID=IVc5 LabelID=IVc6
-
+ 110VLabelID=V32
-
+ 110VLabelID=V33
D34
D35
D36
D37
D38
D39
D40
D41
D42
D43
D44
D45
V
S_46
V
S_47
V
S_48
V
S_49
V
S_50
V
S_51
Model
DModel1
ModelV
SModel1
20.00 22.50 25.00 27.50 30.00 32.50 35.00 37.50 40.00Time [ms]
-1.10
-1.00
-0.38
0.25
0.88
1.10
Y1
Basic_Inverter1Sine Triangle ANSOFT
Curve InfoSINE1.VAL
TRSINE2.VAL
TRSINE3.VAL
TRTRIANG1.VAL
TR
© 2011 ANSYS, Inc. September 29, 2011
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Machine Model in Maxwell - Simplorer
20.00 22.50 25.00 27.50 30.00 32.50 35.00 37.50 40.00Time [ms]
-20.00
-15.00
-10.00
-5.00
0.00
5.00
10.00
15.00
20.00
Y1
[A]
SAS IP, Inc. Basic_Inverter1Currents ANSOFT
Curve InfoRphaseA.I
TRRphaseB.I
TRRphaseC.I
TR
20.00 22.50 25.00 27.50 30.00 32.50 35.00 37.50 40.00Time [ms]
0.00
2.50
5.00
7.50
10.00
12.50
15.00
FEA
1.TO
RQ
UE
SAS IP, Inc. Basic_Inverter1Torque ANSOFT
Curve InfoFEA1.TORQUE
TR
© 2011 ANSYS, Inc. September 29, 2011
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Force Calculations• Force calculation using air gap flux density
• Maxwell Stress Tensor– Force calculation at a point on the stator.– Force on a line in the airgap– Force on a line co-linear with the stator tooth
• Edge Force Density– Default field quantity available in Maxwell– Can be used for creating lumped force
calculations on tooth tips
• Automatic Force mapping from Maxwell to ANSYS Mechanical. (2D-2D, 2D-3D, 3D-3D)
© 2011 ANSYS, Inc. September 29, 2011
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Edge Force Density in Maxwell
0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00Time [ms]
-250.00
-200.00
-150.00
-100.00
-50.00
-0.00
50.00
Forc
e (N
ewto
ns)
02_DC-6step_IPMRadial Force on Tooth Tips ANSOFT
Curve InfoExprCache(ToothTipRadial_Full1)ExprCache(ToothTipRadial_2)ExprCache(ToothTipRadial_3)ExprCache(ToothTipRadial_4)ExprCache(ToothTipRadial_5)ExprCache(ToothTipRadial_6)
0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00Time [ms]
-30.00
-25.00
-20.00
-15.00
-10.00
-5.00
0.00
5.00
10.00
Forc
e (N
ewto
ns)
02_DC-6step_IPMTangential Force on Tooth Tips ANSOFT
Curve InfoExprCache(ToothTipTangent_Full1)ExprCache(ToothTipTangent_2)ExprCache(ToothTipTangent_3)ExprCache(ToothTipTangent_4)ExprCache(ToothTipTangent_5)ExprCache(ToothTipTangent_6)
© 2011 ANSYS, Inc. September 29, 2011
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Eccentricity Model
Right Side Tooth
Left Side Tooth
© 2011 ANSYS, Inc. September 29, 2011
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Parametric Study of Eccentricity Electromagetic Force
• Rotor missaligned0%, 25%, 50%
• Solved simultaneously on multi-core computer
• Shown: Radial Force on Right Tooth Tip
• FFT of Radial Force
© 2011 ANSYS, Inc. September 29, 2011
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Edge Force Density, 50% Eccentricity
© 2011 ANSYS, Inc. September 29, 2011
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50% Eccentricity: Radial and Tangential Force on Right Side and Left Side Tooth
20.00 22.50 25.00 27.50 30.00 32.50 35.00 37.50 40.00Time [ms]
-300.00
-250.00
-200.00
-150.00
-100.00
-50.00
0.00
Forc
e (N
)
Radial Tooth Tip Forces ANSOFT
Curve InfoRadial Force Small GapRadial Force Large Gap
20.00 22.50 25.00 27.50 30.00 32.50 35.00 37.50 40.00Time [ms]
-30.00
-25.00
-20.00
-15.00
-10.00
-5.00
0.00
5.00
10.00
15.00
Forc
e (N
)
Tangential Tooth Tip Forces ANSOFT
Curve InfoTangential Force Small GapTangential Force Large Gap
© 2011 ANSYS, Inc. September 29, 2011
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ANSYS Force Mapping
© 2011 ANSYS, Inc. September 29, 2011
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• Direct Force Mapping– Electromagnetic forces from Maxwell to
Mechanical by linking systems in Workbench
– Transient Analysis for Stress prediction
• Lumped Force Mapping– Tooth Tip objects created for mapping
calculated lumped force using ‘EdgeForceDensity’ in Maxwell.
– Apply these lumped forces manually or through APDL Macro
– Further harmonic and Noise Analysis
Two Approaches
© 2011 ANSYS, Inc. September 29, 2011
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– Case 1: 0% Eccentricity• No misalignment
– Case 2: 50 % Eccentricity• Eccentricity amount is set to
50% of gap width• Creates unbalanced
electromagnetic forces
Approach 1 - Direct Force MappingScenario: Study the effect of Rotor Eccentricity
Peak Edge Force Density 1.5e6 N/m2
Peak Edge Force Density 1.9e6 N/m2
© 2011 ANSYS, Inc. September 29, 2011
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Directional Deformation Radial
• Case 1 0% Eccentricity
• Case 2 50 % Eccentricity
Max Deformation vs time
© 2011 ANSYS, Inc. September 29, 2011
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Von Misses Stress
• Case 1 0% Eccentricity
• Case 2 50 % Eccentricity
Max Stresses vs time
© 2011 ANSYS, Inc. September 29, 2011
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Results: Comparison
• Total Deformation– Deformation higher for eccentric model
• Peak Stresses– Stator Stresses are non symmetric and higher for eccentric model where the air
gap is minimum
Higher the amount of eccentricity, higher is the variation of electromagnetic forces, causing deformation of stator, vibration and noise
Stresses at time=12 ms
© 2011 ANSYS, Inc. September 29, 2011
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Approach 2 Lumped Force Mapping
Electromagnetic Forces
Lumped Forces in Time Domain
Real/Imaginary Forces In Frequency Domain
Harmonic Response
Extract Acoustic Pressures
Export forces
APDL in Workbench
APDL in Workbench
ANSYSMaxwell
ANSYS Mechanical
ANSYSAcoustics
Perform FFT in MaxwellWorkbench Flow Chart forNoise Prediction
© 2011 ANSYS, Inc. September 29, 2011
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ANSYS Harmonic Analysis
© 2011 ANSYS, Inc. September 29, 2011
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Modal Analysis: Get Resonant Frequencies
Mode #1, 8502 Hz Mode #2, 8708 Hz Mode #3, 8708 Hz
Mode #4, 9080 Hz
First four Natural Frequency and corresponding mode shapes
© 2011 ANSYS, Inc. September 29, 2011
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• To make sure that a given design can withstand sinusoidal loads at different frequencies
• To detect resonant response and avoid it if necessary (by using dampers, for example)
• To determine Acoustic response
Boundary Conditions
Input Forces
Appling harmonic forces from Maxwell into ANSYS Mechanical
Why Harmonic Analysis
© 2011 ANSYS, Inc. September 29, 2011
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Harmonic Response – Bode plot
Helps determine that Max Amplitude (1.7mm)occurs at 8710 Hz on the selected vertex
Frequency response at a selected node location of the model.
© 2011 ANSYS, Inc. September 29, 2011
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Amplitude distribution of the displacements at a specific frequency,
Deformation plot at 8710 Hz
Harmonic Response – Contour plot
© 2011 ANSYS, Inc. September 29, 2011
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ANSYS Acoustics
© 2011 ANSYS, Inc. September 29, 2011
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Acoustics Capabilities in ANSYS
• Acoustics is the study of the generation, propagation, absorption, and reflection of sound pressure waves in an acoustic medium.
• Acoustic problems can be identified as
– Vibro-Acoustics: Sound generated structurally (ANSYS Mechanical)
– Aero-Acoustics : Sound generated aerodynamically (ANSYS CFD)
© 2011 ANSYS, Inc. September 29, 2011
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Modeling Aero-Acoustics (ANSYS CFD)
• Free-Space Problem with no solid surfaces:– sound generated from turbulence, jet noise
• Free-Space Problem with solid surfaces:– Fan noise, airframe noise, rotor noise, boundary layer noise,
cavity noise• Interior problem:
• Duct noise, mufflers, ducted fan noise
Sound pressure fluctuations
© 2011 ANSYS, Inc. September 29, 2011
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Vibro-Acoustics (ANSYS Mechanical)Computing the acoustic field radiated by a vibrating structure
• Structure modeled in ANSYS Mechanical where vibration patterns are calculated (Modal, Harmonic Analysis). Applied loads are obtained from Maxwell.
• Vibration patterns used as boundary conditions to compute acoustic field radiated by structure (ANSYS MAPDL, ANSYS Acoustic Structures-ACTRAN)
© 2011 ANSYS, Inc. September 29, 2011
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ANSYS Acoustics Structure
ANSYS Acoustics Structures computes noise radiated by vibrating structures.
From Harmonic Vibrations to Noise Estimates.
ANSYS Acoustics Structures integrates with your current simulation tools.
© 2011 ANSYS, Inc. September 29, 2011
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Acoustic Analysis – Pressure Plot
© 2011 ANSYS, Inc. September 29, 2011
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Acoustic Analysis – Pressure Plot
0.5 m
Pres_1 Pres_2 Pres_3
Freq(Hz)
Pres
sure
(Pa)
Pressure vs Freq
© 2011 ANSYS, Inc. September 29, 2011
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Summary• Investigated different noise sources for electric machines• Demonstrated an integrated approach from Electromagnetics
to Structural to Acoustics.• Showed the effects of static eccentricity on stator tooth forces,
deformation and stresses.• Performed modal analysis to find the acoustic resonances
Future Work:• Investigation of different noise scenarios (machine types, drives)• Include more mechanical details (windings, housing, etc)• Expand harmonic analysis to include higher frequency content of forces• Further investigation of Aero-acoustics with ANSYS CFD
© 2011 ANSYS, Inc. September 29, 2011
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– P. Vijayraghavan, R. Krishnan, “Noise in electric machines: A Review”, IEEE, 1998– K. Shiohata, R. Kusama, S.Ohtsu, T.Iwatsubo, “The Study on Electromagnetic Force
Induced Vibration and Noise from a Normal and Eccentric Universal Motors”, PIERS Proceedings, 2011.
– S. Fink, S. Peters, “Anosft - Noise Prediction for Electrical Motors,” CADFEM/ANSYS Presentation, 2011.
– Wei Wang, Quanfeng Li, Zhihuan Song, Shenbo Yu, Jian Chen, Renyuan Tang, “Three-Dimensional Field Calculation and Analysis of Electromagnetic Vibration and Noise for Disk Permanent Magnet Synchronous Machines”, Shenyang University of Technology, China.
– R. Belmans, D. Verdyck, W. Geysen, R. Findlay, “Electro-Mechanical Analysis of the Audible Noise of an Inverter-Fed Squirrel-Cage Induction Motor”, IEEE, 2008.
– M. Anwar, I. Husain, “Design Perspectives of a Low Acoustic Noise Switched Reluctance Machine”, IEEE, 2000.
– S. Huang, M. Aydin, T.A. Lipo, “Electronmagnetic Vibration and Noise Assessment for Surface Mounted PM Machines,” IEEE, 2001.
– Rakib Islam, Iqbal Hussain, “Analytical Model for Predicting Noise and Vibration in Permanent Magnet Synchronous Motors,” IEEE 2009.
– Pragasen Pillay, William (Wei) Cai, “An Investigation into Vibration in Switched Reluctance Motors,” IEEE Transactions on Industry Applications, Vol. 35, NO. 3, May/June/ 1999.
References
© 2011 ANSYS, Inc. September 29, 2011
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Thank You