Electromagnetic Force Coupling in Electric Machines
Mark Solveson, Cheta Rathod, Mike Hebbes, Gunjan Verma, Tushar Sambharam
ANSYS, Inc. 1
© 2011 ANSYS, Inc.
October 24, 2011
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
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© 2011 ANSYS, Inc.
October 24, 2011
Introduction
• 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
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© 2011 ANSYS, Inc.
October 24, 2011
Machine Types
• 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
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© 2011 ANSYS, Inc.
October 24, 2011
Noise Sources [1]
Magnetic
Mechanical
Aerodynamic
Electronic
Fluid Cooling Phenomena
Radial
Self
Switching Harmonics
Load Induced
Auxiliaries
Slot Harmonics
Stator
Magnetic Unbalance
Couplings
Rotor
Foundation
Modes of Vibration
Bearings
Balancing
Static Eccentricity
Dynamic Eccentricity
Unbalanced Rotor
Audible Frequencies
20 Hz
5
60 Hz
© 2011 ANSYS, Inc.
Elliptical Rotor Surface
261.63 Hz
October 24, 2011
4.186kHz
5 kHz
20 kHz
[1] P. Vigayraghavan, R. Krishnan, “Noise in Electric Machines: A Review,” IEEE, 1998
ANSYS Machine Model
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© 2011 ANSYS, Inc.
October 24, 2011
Electromagnetic Design and Analysis
• 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 Maxwell. SINE1
SINE2
SINE3
TRIANG1
IGBT1
D7
IGBT3
D9
IGBT5
D11
E1
RphaseA
PhaseA_in
PhaseA_out
PhaseB_in
PhaseB_out
PhaseC_in
PhaseC_out
RphaseB
V
+
RphaseC
VM1
MotionSetup1_in
MotionSetup1_out
E2
D8
IGBT2
D10
IGBT4
IGBT6
D12
0

V_ROTB1
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© 2011 ANSYS, Inc.
October 24, 2011
+
Machine Model in Maxwell ‐ Simplorer
2D IPM (Interior Permanent Magnet) motor model created from RMxprt and Maxwell UDP (User Defined Primitive) for rotor
Model
Model
V
DModel1
D40
+
-
D35
S_48
V
S_46
SModel1
D44
V
V
• 4 pole, 1500 RPM, 220 Volt DC bus.
• Two Control Strategies used: • 6 step inverter – In Maxwell
• PWM current regulated – Cosimulation
Maxwell with Simplorer
D42
D37
S_50
D39
110V
LabelID=V32
0
+
-
110V
LabelID=V33
D41
D43
D36
S_49
V
S_47
2.00694ohm
RA
LPhaseA
LabelID=VIB
0.000512893H*Kle
LB
2.00694ohm
RB
LPhaseB
LabelID=VIC
0.000512893H*Kle
LC
2.00694ohm
RC
LPhaseC
D45
V
V
D34
LabelID=VIA
0.000512893H*Kle
LA
D38
S_51
LabelID=IVc1
LabelID=IVc2
LabelID=IVc3
LabelID=IVc4
LabelID=IVc5
LabelID=IVc6
100ohm
100ohm
100ohm
100ohm
100ohm
100ohm
R20
R21
R22
R23
R24
R25
+
-1
+
1V
LabelID=V14
-1
+
1V
LabelID=V15
-1
+
1V
LabelID=V16
-1
+
1V
LabelID=V17
-1
+
1V
LabelID=V18
-1
1V
LabelID=V19
0
SINE1
SINE2
SINE3
TRIANG1
IGBT1
D7
IGBT3
D9
IGBT5
D11
E1
RphaseA
PhaseA_in
PhaseA_out
PhaseB_in
PhaseB_out
PhaseC_in
PhaseC_out
RphaseB
V
Basic_Inverter1
VM1
TR
0.88
MotionSetup1_in
D8
D10
IGBT6
IGBT4
TR
TR
MotionSetup1_out
E2
IGBT2
Sine Triangle
1.10
TR
ANSOFT
Curve Info
SINE1.VAL
SINE2.VAL
SINE3.VAL
TRIANG1.VAL
D12
0

0.25
+
Y1
+
RphaseC
V_ROTB1
-0.38
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© 2011 ANSYS, Inc.
October 24, 2011
-1.00
-1.10
20.00
22.50
25.00
27.50
30.00
Time [ms]
32.50
35.00
37.50
40.00
Machine Model in Maxwell ‐ Simplorer
Torque
SAS IP, Inc.
15.00
Basic_Inverter1
ANSOFT
Currents
SAS IP, Inc.
20.00
Basic_Inverter1
Curve Info
TR
ANSOFT
Curve Info
FEA1.TORQUE
TR
TR
15.00
TR
RphaseA.I
RphaseB.I
RphaseC.I
12.50
10.00
10.00
Y1 [A]
FEA1.TORQUE
5.00
7.50
0.00
-5.00
5.00
-10.00
2.50
-15.00
0.00
20.00
9
22.50
© 2011 ANSYS, Inc.
25.00
27.50
30.00
Time [ms]
October 24, 2011
32.50
35.00
37.50
40.00
-20.00
20.00
22.50
25.00
27.50
30.00
Tim e [ms]
32.50
35.00
37.50
40.00
Force Calculations
• Force calculation using air gap flux density
• Maxwell Stress Tensor [9]
– 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
This is common method in literature. • 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)
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© 2011 ANSYS, Inc.
October 24, 2011
Edge Force Density in Maxwell
Tangential Force on Tooth Tips
02_DC-6step_IPM
ANSOFT
10.00
5.00
Force (Newtons)
0.00
-5.00
-10.00
-15.00
Curve Info
ExprCache(ToothTipTangent_Full1)
-20.00
ExprCache(ToothTipTangent_2)
ExprCache(ToothTipTangent_3)
ExprCache(ToothTipTangent_4)
-25.00
ExprCache(ToothTipTangent_5)
ExprCache(ToothTipTangent_6)
-30.00
0.00
5.00
10.00
15.00
20.00
Time [ms]
25.00
30.00
Radial Force on Tooth Tips
35.00
02_DC-6step_IPM
40.00
ANSOFT
50.00
-0.00
Force (Newtons)
-50.00
-100.00
-150.00
Curve Info
ExprCache(ToothTipRadial_Full1)
ExprCache(ToothTipRadial_2)
ExprCache(ToothTipRadial_3)
-200.00
ExprCache(ToothTipRadial_4)
ExprCache(ToothTipRadial_5)
ExprCache(ToothTipRadial_6)
-250.00
0.00
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© 2011 ANSYS, Inc.
October 24, 2011
5.00
10.00
15.00
20.00
Time [ms]
25.00
30.00
35.00
40.00
Eccentricity Model
Left Side Tooth
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© 2011 ANSYS, Inc.
Right Side Tooth
October 24, 2011
Parametric Study of Eccentricity Electromagetic Force
• Rotor missaligned
0%, 25%, 50%
• Solved simultaneously on multi‐core computer
• Shown: Radial Force on Right Tooth Tip
• FFT of Radial Force
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© 2011 ANSYS, Inc.
October 24, 2011
Edge Force Density, 50% Eccentricity
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© 2011 ANSYS, Inc.
October 24, 2011
50% Eccentricity: Radial and Tangential Force on Right Side and Left Side Tooth
Radial Tooth Tip Forces
0.00
ANSOFT
Tangential Tooth Tip Forces
15.00
ANSOFT
10.00
-50.00
5.00
0.00
Force (N)
Force (N)
-100.00
-150.00
-5.00
-10.00
-200.00
-15.00
-20.00
-250.00
Curve Info
Radial Force Small Gap
Radial Force Large Gap
-300.00
20.00
15
22.50
25.00
© 2011 ANSYS, Inc.
27.50
30.00
Time [ms]
32.50
October 24, 2011
35.00
37.50
Curve Info
Tangential Force Small Gap
Tangential Force Large Gap
-25.00
40.00
-30.00
20.00
22.50
25.00
27.50
30.00
Time [ms]
32.50
35.00
37.50
40.00
ANSYS Force Mapping
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© 2011 ANSYS, Inc.
October 24, 2011
Two Approaches
• Direct Force Mapping
– Electromagnetic forces from Maxwell to Mechanical by linking systems in Workbench
– Maps 2D Edge Force, and 3D Surface force
– 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
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© 2011 ANSYS, Inc.
October 24, 2011
Approach 1 ‐ Direct Force Mapping
Scenario: Study the effect of Rotor Eccentricity
– Case 1: 0% Eccentricity
• No misalignment
– Case 2: 50 % Eccentricity
Peak Edge Force Density 1.5e6 N/m2
• Eccentricity amount is set to 50% of gap width
• Creates unbalanced electromagnetic forces
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© 2011 ANSYS, Inc.
October 24, 2011
Peak Edge Force Density 1.9e6 N/m2
Directional Deformation Radial
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Max Deformation vs time
• Case 1 0% Eccentricity
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© 2011 ANSYS, Inc.
October 24, 2011
• Case 2 50 % Eccentricity
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Von Misses Stress
Max Stresses vs time
• Case 1 0% Eccentricity
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© 2011 ANSYS, Inc.
October 24, 2011
• Case 2 50 % Eccentricity
Results: Comparison
Higher the amount of eccentricity, higher is the variation of electromagnetic forces, causing deformation of stator, vibration and noise
• Total Deformation
– Deformation higher for eccentric model
• Peak Stresses
Stresses at time=12 ms
– Stator Stresses are non symmetric and higher for eccentric model where the air gap is minimum
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© 2011 ANSYS, Inc.
October 24, 2011
Approach 2 Lumped Force Mapping Electromagnetic Forces
Export forces
ANSYS
Maxwell
Workbench Flow Chart for
Noise Prediction
Lumped Forces in Time Domain
Perform FFT in Maxwell
Real/Imaginary Forces In Frequency Domain
APDL in Workbench
ANSYS Mechanical
Harmonic Response
APDL in Workbench
ANSYS
Acoustics
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© 2011 ANSYS, Inc.
October 24, 2011
Extract Acoustic Pressures
ANSYS Harmonic Analysis
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© 2011 ANSYS, Inc.
October 24, 2011
Modal Analysis: Get Resonant Frequencies
Mode #1, 8502 Hz
Mode #2, 8708 Hz
Mode #3, 8708 Hz
First four Natural Frequency and corresponding mode shapes
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© 2011 ANSYS, Inc.
October 24, 2011
Mode #4, 9080 Hz
Why Harmonic Analysis
•
To make sure that a given design can withstand sinusoidal loads at different frequencies
•
To detect resonant response and avoid it if necessary (e.g. using mechanical dampers, changing PWM frequency, etc.)
•
To determine Acoustic response
Boundary Conditions
Input Forces
Appling harmonic forces from Maxwell into ANSYS Mechanical
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© 2011 ANSYS, Inc.
October 24, 2011
Harmonic Response – Bode plot
Frequency response at a selected node location of the model. Helps determine that Max Amplitude (1.7mm)
occurs at 8710 Hz on the selected vertex
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© 2011 ANSYS, Inc.
October 24, 2011
Harmonic Response – Contour plot
Amplitude distribution of the displacements at a specific frequency, Deformation plot at 8710 Hz
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© 2011 ANSYS, Inc.
October 24, 2011
ANSYS Acoustics
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© 2011 ANSYS, Inc.
October 24, 2011
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)
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© 2011 ANSYS, Inc.
October 24, 2011
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
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© 2011 ANSYS, Inc.
October 24, 2011
Vibro‐Acoustics (ANSYS Mechanical)
Computing the acoustic field radiated by a vibrating structure
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•
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)
© 2011 ANSYS, Inc.
October 24, 2011
Acoustic Analysis – Pressure Plot
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This image cannot currently be display ed.
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© 2011 ANSYS, Inc.
October 24, 2011
Acoustic Analysis – Pressure Plot
0.5 m
Pres_2
Pres_3
Pressure vs Freq
Pressure (Pa)
Pres_1
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© 2011 ANSYS, Inc.
October 24, 2011
Freq(Hz)
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
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© 2011 ANSYS, Inc.
October 24, 2011
References
[1] P. Vijayraghavan, R. Krishnan, “Noise in electric machines: A Review”, IEEE, 1998
[2] 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. [3] S. Fink, S. Peters, “Ansoft ‐ Noise Prediction for Electrical Motors,” CADFEM/ANSYS Presentation, 2011.
[4] 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. [5] 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.
[6] M. Anwar, I. Husain, “Design Perspectives of a Low Acoustic Noise Switched Reluctance Machine”, IEEE, 2000.
[7] S. Huang, M. Aydin, T.A. Lipo, “Electronmagnetic Vibration and Noise Assessment for Surface Mounted PM Machines,” IEEE, 2001.
[8] Rakib Islam, Iqbal Hussain, “Analytical Model for Predicting Noise and Vibration in Permanent Magnet Synchronous Motors,” IEEE 2009. [9] 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.
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© 2011 ANSYS, Inc.
October 24, 2011
Thank You
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© 2011 ANSYS, Inc.
October 24, 2011
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.
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© 2011 ANSYS, Inc.
October 24, 2011
Title and Abstract
Electromagnetic Force Coupling in Electric Machines Including Stress, Deformation, and Acoustic Analysis.
Understanding the impact of electromagnetic forces on noise generation for electric machines can include many factors. This presentation will review these issues and illustrate electromagnetic forces, stress, deformation, and acoustic coupling in ANSYS Workbench. An example showing automatic mapping of magnetic time‐domain forces, and a comparison of stresses for different rotor eccentricities will be shown.
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© 2011 ANSYS, Inc.
October 24, 2011
Presentation Outline (Goal 30 total Slides)
1.
Introduction
2.
Literature review – what are the noise comonents for electric machines
a.
b.
3.
EM Motor Methodology
a.
b.
c.
4.
Noise Sources, examples
Acoustic Definition, examples
RMxprt to Maxwell, Simplorer
Force calculations
Eccentricity Model
Mechanical Analysis
a. 2D (3D?) transient force mapping results
b. Discussion of FFT approaches (by inspection or 3rd party tools/scripts)
c. 2D (3D?) harmonic Analysis 5.
Acoustic analysis
a. General capabilities (acoustic elements, Actran coupling? )
b. Results for stator lamination
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© 2011 ANSYS, Inc.
October 24, 2011
Noise Sources
• Magnetic
– The interaction of magnetic fields and currents in the machine cause electromagnetic torque and thus rotation of the rotor. – Evaluation of the radial and tangential forces on the tooth tips are important.
• This can be accomplished through evaluation of the air gap flux density, or using Force Density field calculations available within Maxwell. – If one of the radial force frequencies coincides with the natural frequency of the machine, resonance occurs leading to acoustic noise. • Mixed product of stator and rotor winding space harmonics.
• Slot Harmonics
• Rotor Eccentricity: improper rotor alignment causing unbalanced magnetic forces on the stator. – Lamination vibration due to magnetorestrictive forces (worst when not stacked properly)
• Electronic
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– Switching noise • Inverter PWM frequencies can be in audible range.
© 2011 ANSYS, Inc.
October 24, 2011
– Current through the winding –
Lorentz forces
Noise Sources
• Mechanical
– Self resonance – natural resonance frequencies
• Closed form equations
• FEA
– Load induced
• Coupling of machine to load, and mounting.
– Auxiliaries
• Bearing Vibration
• Brush commutators
– Chattering
• Intra‐lamination • Function of Bolt force
• Involves 3D Mechanical transient vibration analysis
– Manufacturing asymmetries of the rotor and stator‐ nonuniform air gap
– Stator winding which are not installed properly
• Aero‐Dynamics
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© 2011 ANSYS, Inc.
October 24, 2011
– ANSYS CFD
Machine Model in Maxwell
• VB script Fields Calculator to create Radial and Tangential Force Expressions from EdgeForceDensity
• VB script Calculates Radial and Tangential Force on Tooth Tips • Allows only force on edge that neighbors non ferrous objects
• ‘Half’ teeth force components added together
• Add to Expression Cache
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© 2011 ANSYS, Inc.
October 24, 2011
Harmonic Analysis Overview
A technique to determine the steady state response of a structure to sinusoidal (harmonic) loads of known frequency.
Input:
• Harmonic loads (forces, pressures, and imposed displacements) of known magnitude and frequency. (Obtained from Maxwell)
• May be multiple loads all at the same frequency. Output:
• Harmonic displacements at each DOF, usually out of phase with the applied loads.
• Other derived quantities, such as stresses and strains.
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© 2011 ANSYS, Inc.
October 24, 2011
ANSYS Acoustics
•
Structural‐borne noise (one way Vibro‐Acoustics)
– ANSYS Acoustics Structures (FFT’s ACTRAN Solver)
•
Vibro‐Acoustics – ANSYS Mechanical (APDL Solver)
•
Aero‐Acoustics
– ANSYS CFD
•
Nonlinear fluid‐structure interaction
– ANSYS CFD + ANSYS Mechanical
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© 2011 ANSYS, Inc.
October 24, 2011
Aero‐Acoustics ANSYS CFD Approaches
• Direct calculation: •
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– Resolve the acoustic pressure fluctuations as part of the CFD solution
Couple CFD with specialized acoustics codes, Boundary Element Methods (BEM), Hybrid zonal methods – Acoustic waves are not tracked with CDF solution
– Calculate wave propagation using specialized codes (ACTRAN, SYSNOISE) © 2011 ANSYS, Inc.
October 24, 2011
Aero‐Acoustic simulation of Automotive Front End Module cooling fans by using FLUENT’s Acoustic module Courtesy of Hyundai MOBIS, Korea
Computational domain
Geometry of Cooling Fans
Pressure Contours
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© 2011 ANSYS, Inc.
October 24, 2011
Sound pressure fluctuations
Flow Pathlines through calculated at the receiver position Subwoofer Example (ANSYS CFD)
(non‐linear fluid with structure)
Fluid‐Structure Interaction Solution
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© 2011 ANSYS, Inc.
October 24, 2011
Transient Pressures
Acoustic ‐ Structural Example ‐ Coupled
Acoustic Energy Source
Target Object:
Nested Cylindrical Cans Scattered Acoustic Radiation Animation of Acoustic Pressure (Pa) FEA Model quarter Symmetry Hemispherical Domain
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© 2011 ANSYS, Inc.
October 24, 2011