Electromagnetic Force Coupling Electric Machines

8/17/2019 Electromagnetic Force Coupling Electric Machines

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© 2011 ANSYS, Inc. October 24, 20111

Electromagnetic Force

Coupling in Electric Machines

Mark Solveson, Cheta Rathod, Mike Hebbes,

Gunjan Verma, Tushar Sambharam

ANSYS, 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

0

IGBT3

IGBT2D10

D11

D8

IGBT1

IGBT4

IGBT5D7

D12

D9

IGBT6

SINE2SINE1 SINE3

TRIANG1

+ V

V M1

E1

E2

RphaseA

RphaseB

RphaseC

+

V_ROTB1

PhaseA_in

PhaseB_in

PhaseC_in

MotionSetup1_in

PhaseA_out

PhaseB_out

PhaseC_out

MotionSetup1_out


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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

2.00694ohm

RA

2.00694ohm

RB

2.00694ohm

RC

0.000512893H*Kle

LA

0.000512893H*Kle

LB

0.000512893H*Kle

LC

LabelID=VIA

LabelID=VIB

LabelID=VIC

+ -11VLabelID=V14

+ -11VLabelID=V15

+ -11VLabelID=V16

+ -11VLabelID=V17

+ -11VLabelID=V18

+ -11VLabelID=V19

100ohm

R20

100ohm

R21

100ohm

R22

100ohm

R23

100ohm

R24

100ohm

R25

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

0

IGBT3

IGBT2D10

D11

D8

IGBT1

IGBT4

IGBT5D7

D12

D9

IGBT6

SINE2SINE1 SINE3

TRIANG1

+ V

V M1

E1

E2

RphaseA

RphaseB

RphaseC

+

V_ROTB1

PhaseA_in

PhaseB_in

PhaseC_in

MotionSetup1_in

PhaseA_out

PhaseB_out

PhaseC_out

MotionSetup1_out

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

Y 1

Basic_Inverter1Sine Triangle ANSOFT

CurveInfo

SINE1.VALTR

SINE2.VALTR

SINE3.VALTR

TRIANG1.VALTR


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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

Y 1 [ A ]

SAS IP, Inc. Basic_Inverter1Currents ANSOFT

Curve Info

RphaseA.ITR

RphaseB.ITR

RphaseC.ITR

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

F E A 1 . T O R Q U E

SAS IP, Inc. Basic_Inverter1Torque ANSOFT

Curve Info

FEA1.TORQUETR


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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

-200.00

-150.00

-100.00

-50.00

-0.00

50.00

F o r c e ( N e w t o n s )

02_DC-6step_IPMRadial Force on Tooth Tips ANSOFT

Curve Info

ExprCache(ToothTipRadial_Full1)ExprCache(ToothTipRadial_2)

ExprCache(ToothTipRadial_3)




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

F o r c e ( N e w

t o n s )

02_DC-6step_IPMTangential Force on Tooth Tips ANSOFT

Curve Info

ExprCache(ToothTipTangent_Full1)

ExprCache(ToothTipTangent_2)






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Eccentricity Model

Right Side

Tooth

Left Side

Tooth


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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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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

F o r c e ( N )

Radial Tooth Tip Forces ANSOFT

Curve Info

Radial Force Small Gap

Radial 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

F o r c e ( N )

Tangential Tooth Tip Forces ANSOFT

Curve Info

Tangential Force Small Gap

Tangential Force Large Gap


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ANSYS Force

Mapping


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• 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

Two 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 Mapping

Scenario: 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: 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


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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

ANSYS

Maxwell

ANSYS

Mechanical

ANSYS

Acoustics

Perform FFT in Maxwell

Workbench

Flow Chart

for

Noise Prediction


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ANSYS Harmonic

Analysis


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Modal Analysis: Get Resonant Frequencies

Mode #1, 8502 Hz Mode #2, 8708 HzMode #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_2Pres_3

Freq(Hz)

P r e s s u r e

( P a )

Pressure vs Freq


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Summary

• Investigated different noise sources for electric machines

• 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


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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.


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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.

Title and Abstract


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1. Introduction

2. Literature review – what are the noise comonents for electric machines

a. Noise Sources, examples

b. Acoustic

Definition,

examples

3. EM Motor Methodology

a. RMxprt to Maxwell, Simplorer

b. Force calculations

c. Eccentricity Model

4. 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

Presentation Outline (Goal 30 total Slides)


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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 – Switching noise

• Inverter PWM frequencies can be in audible range.

– Current through the winding – Lorentz forces


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• 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

– ANSYS CFD

Noise Sources


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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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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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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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Aero‐Acoustics ANSYS CFD Approaches

• Direct calculation:

– 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)


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Aero‐Acoustic simulation of Automotive

Front End

Module

cooling

fans

by using FLUENT’s Acoustic module Courtesy of Hyundai MOBIS, Korea

Geometry of Cooling Fans

Computational

domain

Pressure Contours Flow Pathlines through

Sound pressure

fluctuations

calculated at the

receiver position

S b f E l (ANSYS CFD)


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Subwoofer Example (ANSYS CFD)

(non‐linear

fluid

with

structure)

Fluid‐Structure Interaction Solution Transient Pressures


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Scattered Acoustic

Radiation

Acoustic Energy

Source

Target Object:

Nested Cylindrical

Cans

Acoustic ‐ Structural Example ‐ Coupled

FEA Model

quarter Symmetry

Hemispherical

Domain

Animation of Acoustic

Pressure (Pa)

Electromagnetic Force Coupling Electric Machines

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