Electromagnetic Force Coupling in Electric Machines - … · Electromagnetic Force Coupling in ... •Single and Three Phase Induction Machines. ... Noise Prediction for Electrical

© 2011 ANSYS, Inc. September 21, 2011

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Electromagnetic Force Coupling in Electric Machines

Mark Solveson, Cheta Rathod, Mike Hebbes, Gunjan Verma, Tushar SambharamANSYS, Inc.


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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


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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


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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


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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


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ANSYS Machine Model


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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 Maxwell.

Electromagnetic Design and Analysis


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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 Simplorer

0

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


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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


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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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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

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-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)


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Eccentricity Model

Right Side Tooth

Left Side Tooth


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Parametric Study of Eccentricity Electromagetic Force

• Rotor missaligned by0%, 25%, 50% of total airgap

• Solved simultaneously on multi-core computer

• Shown: Radial Force on Right Side Tooth Tip

• FFT of Radial Force (with log scaling)


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Edge Force Density, 50% Eccentricity


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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


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ANSYS Force Mapping


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1. Direct Force Mapping– Electromagnetic force density from

Maxwell to Mechanical by linking systems in Workbench

– Maps 2D Edge Force Density, and 3D Surface Force Density at all points in the objects

– For Transient Mechanical Analysis and Stress Prediction

2. Lumped Force Mapping– Tooth Tip objects created for mapping

– Calculate lumped force by integrating

‘EdgeForceDensity’ in Maxwell.

– Apply these lumped forces manually

or through APDL Macro

– For harmonic and Noise Analysis

Two Coupling Approaches


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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


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Directional Deformation Radial

• Case 1 0% Eccentricity

• Case 2 50 % Eccentricity

Max Deformation vs time


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Von Misses Stress

• Case 1 0% Eccentricity

• Case 2 50 % Eccentricity

Max Stresses vs time


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Results for Offset Rotor using Direct Force Mapping

• 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


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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 on tooth tips

APDL in Workbench

APDL in Workbench

ANSYSMaxwell

ANSYS Mechanical

ANSYSAcoustics

Perform FFT in MaxwellWorkbench Flow Chart forNoise Prediction


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ANSYS Harmonic Analysis


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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


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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 (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

Why Harmonic Analysis


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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.


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Amplitude distribution of the displacements at a specific frequency

Deformation plot at 8710 Hz

Harmonic Response – Contour plot


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ANSYS Acoustics


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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)


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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


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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)


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Acoustic Analysis – Pressure Plot


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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


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Summary

• Discussed different noise sources for electric machines (magnetic, mechanical, aerodynamic, electronic)

• Demonstrated an integrated approach from Electromagneticsto 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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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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Thank You

Documents

Electromagnetic Force Coupling in Electric Machines - … · Electromagnetic Force Coupling in ... •Single and Three Phase Induction Machines. ... Noise Prediction for Electrical