NOISE AND VIBRATIONS IN ELECTRIC MACHINES - … · 2017-11-20 · NOISE AND VIBRATIONS IN ELECTRIC MACHINES ... • New topologies with higher Noise, Vibration, Harshness (NVH)

NOISE AND VIBRATIONS IN ELECTRIC MACHINESReview of NVH sources & mitigation of electromagnetically-excited noise

LE BESNERAIS Jean

REGNIEZ Margaux

21th September2017

[email protected]

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EOMYS ENGINEERING

• Innovative Company created in may 2013 in Lille, North of France (1 hr from Paris)

• Activity: engineering consultancy / applied research

• R&D Engineers in electrical engineering, vibro-acoustics, heat transfer, scientific

computing

• 80% of export turnover in transportation (railway, automotive, marine, aeronautics),

energy (wind, hydro), home appliances, industry

• Diagnosis and problem solving including simulation & measurements

• Multiphysic design optimization of electrical systems

• Technical trainings on vibroacoustics of electrical systems

• MANATEE simulation software for the integrated electromagnetic and vibro-

acoustic design optimization of electric machines

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EOMYS can be involved both at design stage & after manufacturing of electric machines

SERVICES & PRODUCTS

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WEBINAR SUMMARY

• INTRODUCTION

• REVIEW OF NOISE & VIBRATIONS IN ELECTRIC MACHINES

• FOCUS ON MAGNETIC NOISE AND VIBRATION MITIGATION

• MODELING & SIMULATION OF ELECTROMAGNETICALLY-EXCITED NOISE

• CONCLUSION

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Why vibro-acoustics are important when designing electrical machines?

• Cost optimization leads to less stiff magnetic cores, increasing vibration & noise levels

• Skewing technique degrades torque and efficiency and can be avoided with a good NVH design

• New topologies with higher Noise, Vibration, Harshness (NVH) challenges: concentrated winding PMSM,

brushless DFIM

• Additionnal cost, weight, and delays may come when solving vibration and noise issues after manufacturing

Importance of noise & vibration analysis

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Review of noise sources in electric machines

aerodynamic sources

(e.g. fans)

electromagnetic sources

(e.g. slot/magnet)

mechanical sources

(e.g. bearings, gearbox)

Noise of an electric traction machine during starting:

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• Bearings

• Shaft imbalance

• Shaft eccentricity

• Sliding contacts

- between rotor and bearings

- slip rings

- metal or carbon brushes

• Geared power transmission motor coupling

• Tightening fault

[Bertolini2012]

Contributors to mechanical noise

Mechanical noise and vibration sources

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Causes of mechanical noise and vibrations

Bearing noise and vibrations

• Journal bearings / Sleeve bearings

• Fluid bearings

- Floating bearings – oil film bearings

- Air bearings

• Ball bearings / Roller bearings

- “simple” ball bearings

- ball bearings with squeeze film dampers

Roughness of sliding surfaces

Lubrication fault

Manufacturing faults

Instability of oil film in bearing

Manufacturing faults (sphericity, waviness)

Presence of dirt / lubrication fault

Resonance of outer ring (natural frequencies)

Alignment fault (mounting) / shaft resonances

Noise depends on and can be modified by- Running speed- Load- Temperature- Alignment fault

[Momono1999][Sterling2009]

Rotor response orbit (oil whirl)

Rotor response orbit (inner & outer oil whirl)

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Frequency content


• Flow-induced vibrations due to instability of oil film in bearings

- Nonlinear characteristics of stiffness and damping coefficients of oil-film bearings

- Oil whirl (case of full-floating bearings) at subsynchronous frequency

[Sterling2009]

Excessive unbalance Rotor misalignment Contact rub between rotor and bearings

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Frequency content

• Ball bearings

- Balls frequency rotational frequency (FT) ��

�� 1 �

�cos�

- Balls passage frequency on outer raceway (FPE) ��

�� 1 �

�cos�

- Balls passage frequency on inner raceway (FPI) ��

�� 1 �

�cos�

- Balls rotational frequency (FRB) ��

�� 1 �

�

�

cos��

- Flaw noise

- Contamination noise (due to dirt)

[Vijayraghavan1999][Momono1999][Augeix]

Structural fault

Handling

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Mechanical noise mitigation


• Modification of damaged ball bearing

• Use of chemical additives

• Use of vibration absorption or vibration isolation device

• Modification of rotating speed

• Use of alignment tools when mounting the motor

• Application of axial pre-load by means of coil springs

• Addition of elastic damping elements in bearing housing

• Application of shield or seal to prevent dirt from entering the bearing

• Dynamic rotor balancing

[Vijayraghavan1999][Tillema2003]

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Causes of aerodynamic noise and vibrations

• Air flow in electrical machine (high speed) centrifugal fan

• Cooling system

- air (fan)

-> fan rotating with electrical machine

-> fan rotating independently

- water

- oil

[Guédel][Parrang2016][Vijayraghavan1999]

Examples of water jackets, from[Satrustegui2017]

-> external pump-> fluid flow and interaction with obstacles

Acoustic radiation

Natural convection

Forced convection

Shaft-mounted fan

Aerodynamic noise and vibration sources

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Frequency content

Aerodynamic noise and vibrations

• Mechanisms of flow noise generation

- Monopolar noise harmonic noise

=> due to quick variations of flow rate imposed by obstacles in flow

- Dipolar noise harmonic or broadband noise (depending on periodicity of load)

=> due to load fluctuations imposed by the fluid on obstacles

- Quadripolar noise broadband noise

=> directly generated inside the flow due to shear strains induced by turbulences in the fluid

• Fan noise at characteristic frequencies

- Vortex frequency: �� 0,185�

�

- Fan blades frequency: ��

�

- Cooling air passing through rotor ducts frequency: �!" � #!�

�

[Guédel][Parrang2016][Vijayraghavan1999]

Rotation speed (RPM)

Number of blades Rotation speed (RPM)

Number of rotor slots

Air stream velocity (m/s)

Diameter of the fan (m)

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Aerodynamic noise mitigation

Aerodynamic noise and vibrations

• Blade geometry (circular to aerofoil cross-section) => no more vortex frequency

• Minimum distance between fan blades and stationary obstacle

• Reduction of number of rotor vents and lining air chambers with sound absorbent insulation

• Unevenly spaced fan blades (caution with unbalance)

• Reduction of fan diameter

• Texturing on blades

• Use of porous material for fan blades

• Use of axial fan rather than radial fan

[Vad2014][Wang2016][Vijayraghavan1999][Mizuno2013]

Example of texture, from [Wang2016]

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Causes of magnetic noise and vibrations

• Dynamic magnetic forces apply to active materials (laminations, magnets, windings)

• Magnetic forces include magnetostrictive & Maxwell forces

• Magnetostriction can be neglected

• Maxwell forces tend to bring stator closer to rotor (minimum reluctance / maximum flux)

Electromagnetic noise and vibration sources

Magnetostriction forces

Maxwell / reluctance forces

[Laftman 1995]

see video at https://eomys.com/ressources/article/videos?lang=en

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Causes of magnetic noise and vibrations

• Maxwell force harmonics include the effects of

- pole/slot harmonics

- time harmonics (Pulse Width Modulation)

- saturation harmonics

- winding harmonics

- eccentricities harmonics

• Resonance is due to frequency and spatial distribution match of excitingforces with stator/rotor structural modes

Electromagnetic noise and vibration sources

Noise harmonic analysis of a PMSM with MANATEE software

resonance

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Frequency content

�$%&" � �$�'$ ()

*� 0,+2

Electromagnetic noise and vibrations

• Complex spectrum due to 2D phenomenon

- wavenumber r: space frequency along the airgap- frequency f: time frequency

• Lowest wavenumbers give highest vibrations due to lower yoke stiffness

• Slotting effect in induction machines mainly occur at

r=0 r=+/-1 r=+/2

-$%&" � #! � #$ � 0,+2.

�$%&" � 2/0�$

• Slotting effect in permanent magnet synchronous machines mainly occur at

-$%&" � 012 #$, 2.

s slipfs fundamental electrical frequencyp pole pair number

012 #$, 2. � |/02. � 40#$|

u0 minimum positive integerv0 relative integerGCD=Greatest Common Divider

Ex: Zs=12 p=5 GCD=2=|1*10-1*12| -> u0=1, first excitation with r=2 occurs at 2x1fs= 2fsGCD=2=|5*10-4*12| -> u=5, another excitation with r=2 occurs at 2x5fs=10fsGCD=2=|7*10-6*12| -> u=7, another excitation with r=2 occurs at 2x7fs= 14fs

Ex: Zs=36 Zr=28 p=3 -> an excitation of wavenumber r=-2=28-36+6 occurs at fs(Zr/p+2)

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Frequency f

Wavenumbers r

r=Mc

2u0f s

2(u

0+Zs/Mc)fs

2(u

0-Zs/Mc)fs

Frequency spacing=LCM(Zs,2p)fR

r=2Mc

4u0f s

Wavenumber spacing=GCD(Zs,2p)

2(u

0+2Zs/Mc)fs

2(2u0+Zs/Mc)fs

Ncf s/p

2N

cf s/p

-Ncf s/p

n=2

n=1

n=0r=0

• General pattern of harmonic forces in PMSM open-circuit conditions

Frequency content

Electromagnetic noise and vibrations GCD=Greatest Common DividerLCM=Least Common MultipleMc=GCD(Zs,2p)Nc=LCM(Zs,2p)NcMc=Zs2p

r=0 cogging torque/pulsating radial force

other radial & tangential force harmonics

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Transfer path analysis


Wave-number

Force direction

Transfer path Description

r>0 Radial,tangential

Air borne Radial circumferential deflection of the outer stator yokeand frame or outer rotor (rotating in forced regime,pulsating at resonance)

r=0 Radial Air borne Radial pulsating circumferential deflection of the statoryoke and frame or outer rotor

r=0 Tangential(cogging torque/ torque ripple)

Structural borne Propagation of rotor torsional vibration to rotor shaft lineand gearbox mount, or bearing sleeves and outer statorframe

r=0 Tangential(cogging torque/ torque ripple)

Air borne Deflection of the outer stator yoke and frame or outerrotor following a unbalanced torsional mode due toparticular boundary conditions

r=1 Radial(unbalancemagnetic pull)

Air borne Bending / tilting deflection of the outer stator frame orouter rotor, in particular in clamped-free conditions

r=1 Radial(unbalancemagnetic pull)

Structural borne Propagation of rotor bending vibration to rotor shaft lineand gearbox mount, or bearing sleeves and outer statorframe

Axial Air borne Axial deflection of the end-shields

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Magnetic noise mitigation (general)

• Avoid resonance between magnetic forces & structural modes (simulation recommended)

• Reduce asymmetries so tolerances on- eccentricities- magnet position / magnetization- lamination roundness


Effect of stator roundness on variable speed sound level using MANATEE software (left: circular stator, right: elliptical stator shape)

Effect of rotor slot number on maximum noise of an induction motor using MANATEE software

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Magnetic noise mitigation (magnetics)

• Skewing

• Pole shaping

• Modulation of pole width / position

• Modulation of slot width / position

• Notches

• Flux barriers

• Airgap increase


Effect of a PMSM rotor skew angle on acoustic noise (MANATEE software)

Use of rotor notch to mitigate acoustic noise (MANATEE software)

Example of stepped-skew PMSM rotor

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Magnetic noise mitigation (control)

• Spread spectrum switching strategies

• Harmonic current injection

• Load angle


Magnetic noise mitigation (structural)

• Lamination geometry (static + natural frequencies)

• Damping

• Coupling between housing & lamination

• Structural spacers

Effect of harmonic current injection on noise level (MANATEE software)

0 10 20 30 40 50 60 70 80 90 1002000

2500

3000

3500

4000

4500

5000

5500

6000

6500

Stator yoke [mm]

Fre

qu

en

cy

[Hz]

Frequency variation of m=0 mode

Effect of yoke height change on breathing mode natural frequency (MANATEE software)

[Masoudi2013][Rasmussen2001]

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ELECTRICAL MODEL

ELECTROMAGNETIC MODEL

STRUCTURAL MODEL

ACOUSTIC MODEL

Analytical Analytical PWM generationExtended equivalent circuitsSaturation coefficient

Numerical Circuit simulation (ODE)

Analytical Permeance / mmfwinding function

Semi-analytical

Subdomain modelsComplex permeanceConformal mapping

Numerical Non linear electromagnetic FEM

Analytical 2D equivalent shell deflections2D/3D natural frequencies with tooth correction factors

Semi-analytical

Green’s function for the vibration responseSEA

Numerical Structural FEM

Analytical Equivalent radiation efficiency

Semi-analytical

Dipole field expansionSEA

Numerical Acoustic FEM/BEM

Fully analyticalFully numericalHybrid (preferred)

Output: rotor & stator currents Output: time and space distribution of radial & tangential airgap flux density

Output: radial vibration of the outer surface

Output: acoustic noise spectrum

strong circuit coupling

Modelling and simulation of electromagnetic noise & vibrations

Overall simulation workflow (weak coupling)

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Available electromagnetic NVH simulation software

VWP Virtual Work PrincipleMT Maxwell Tensor

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Conclusions on available software solutions

• All electromagnetic FEA software now propose a coupling with NVH tools

• Electromagnetic FEA software only offer a direct coupling approach with structural mechanics

• Multiphysic software like Comsol / Ansys Workbench do not give ready-to-use multiphysic simulation workflow

• MANATEE is the only software with:

- indirect coupling approach (Electromagnetic Vibration Synthesis) to speed up simulation time

- semi-analytical models and model hybridation to be used in early design phase

- an integrated multiphysic simulation process

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Limitations of fully numerical approaches

• Variable-speed vibroacoustic simulation including switching effects up to 10 kHz can take several days of simulation

• Numerical noise (remeshing ripple) can appear and sound power level may be wrong due to spurious inter-harmonics (continuous sound spectrum Vs discrete excitations)

• Missing validation of magnetic force calculation & mesh to mesh projection techniques

[Pellery2012][LeBesnerais2016]

[Magnet website]

[Peters2011]

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Recommended simulation workflow

• Use of semi-analytical models (subdomain + equivalent cylinder) for the variable speed NVH simulation of electric machines during early electromagnetic design loops

Comparison between FEA and subdomain electromagneticmethods in MANATEE software (left: SPMSM, right: SCIM)

• Use of finite element models (electromagnetics + structural mechanics) combined with ElectromagneticVibration Synthesis algorithm in detailed mechanical design phase

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Electromagnetic Vibration Synthesis (from MANATEE software)

Tangential and radial harmonic magnetic forces (magnitude,

wavenumber, frequency, phase)

3D airgap flux distribution

HARMONIC FORCE PROJECTION

r=2 r=3

ELECTROMAGNETIC MODEL

r=0

STRUCTURAL MODEL

Unit harmonic loads for wavenumbers

r=0, ±2, ±4 …

STRUCTURAL FREQUENCY RESPONSE FUNCTIONS

r=0 r=2

ELECTROMAGNETIC VIBRATION SYNTHESIS

Complex FRFs (radial & tangential) for each

wavenumber r

Vibration and noise spectrogramsOperational Deflection Shapes

Modal contributionRadiating surface velocities

• 2D or 3D external FEA software (Flux, Jmag, Maxwell, Magnet etc…)

• Manatee 2,5D analytic model• Manatee 2,5D semi analytic model• Manatee 2,5D numerical model (FEMM)

• 3D external FEA software (Optistruct, Ansys)

• Manatee 2,5D analytic model• Manatee numerical model (GetDP)

Torque/speed curve (variable speed control law)

SPECTROGRAM SYNTHESIS

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Examples of experimental validation with obtained with MANATEE software

Sound level during a run-up (experiments with gearbox+water-

cooling+converter harmonics)

Sound level during a run-up (MANATEE simulation without

converter harmonics)~10 seconds on a laptop

TESTS MANATEE

Motor A

Motor B-40 dB

-> Semi-analytical models of MANATEE software can be successfully applied during first

electromagnetic design loops, even when neglecting saturation and housing effect

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• A good vibro-acoustic design can be carried without skewing, thus improving electric machine efficiency

• Magnetic noise & vibrations should be considered at the early electromagnetic design stage

• Numerical models can be accelerated using Electromagnetic Vibration Synthesis algorithm in detailed

design phase of electric motors

• Experiments should always be used to improve the simulation model accuracy (e.g. quantification of modal

damping)

Conclusions

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THANK YOU FOR YOUR ATTENTIONwww.eomys.com

Q&A SESSION

For other EOMYS webinars, go to https://eomys.com/ressources/webinaires/?lang=en

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REFERENCES

[Vijayraghavan1999] P. Vijayraghavan, R. Krishnan, Noise in electric machines: a review, IEEE Transactions on Industry Applications 35(5), 1999. (Warning this reference is not reliable for electromagnetically-excited noise & vibrations)

[Guédel] A. Guédel, Bruit des ventilateurs, Techniques de l’ingénieur.

[Wang2016] Y. Wang et al., Numerical investigation of the passive control of cavity flow oscillations by a dimpled non-smooth surface, Applied Acoustics 111, 2016.

[Vad2014] J. Vad et al., Aerodynamic and aero-acoustic improvement of electric motor cooling equipment, J. Power and Energy 228(3), 2014.

[Parrang2016] S. Parrang, Prédiction du niveau de bruit aéroacoustique d'une machine haute vitesse à reluctance variable, Thèse ENS Cachan, 2016.

[Mizuno2013] S. Mizuno et al., Development of a totally enclosed fan-cooled traction motor, IEEE Trans. Indus. Appl. 49(4), 2013.

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REFERENCES

[Sterling2009] J. Sterling, Influence of induced unbalance on subsynchronous vibrations of an automotive turbocharger, 2009.

[Nguyen2015] H. Nguyen-Schäfer, Rotordynamics of automotive turbochargers, 2015.

[Kirk2011] R.G. Kirk et al., Turbocharger vibration show nonlinear jump, JVC 18(10), 2011.

[Kirk2010] R.G. Kirk et al., Turbocharger on-engine experimental vibration testing, JCV 16(3), 2010.

[Kirk2006] R.G. Kirk et al., Stability analysis of a high speed automotive turbocharger, IJTC 2006.

[Ishida2012] Y. Ishida and T. Yamamoto, Linear and nonlinear rotordynamics, Wiley 2012.

[Bekemans2006] M. Bekemans, Modélisation des machines électriques en vue du contrôle des efforts radiaux, PhD thesis, UCL, 2006.

[Tillema2003] H.G. Tillema, Noise reduction of rotating machinery by viscoelastic bearing supports, PhD thesis, Twente University, 2003.

[Vijayraghavan1999] P. Vijayraghavan, R. Krishnan, Noise in electric machines: a review, IEEE Transactions on Industry Applications 35(5), 1999.

[Momono1999] T. Momono and B. Noda, Sound and Vibration in Rolling bearings, Motion & Control 6, 1999.

[Augeix] D. Augeix, Analyse vibratoire des machines tournantes, Techniques de l’ingénieur.

[Bertolini2012] T. Bertolini and T. Fuchs, Vibrations and noises in small electric motors, Faulhaber, 2012.

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REFERENCES

[Laftman1995] L Laftman “The contribution to noise from magnetostriction and PWM inverter in an induction machine” PhD dissertation, University of Lund, 1995

[Rasmussen2001] P. O. Rasmussen, J. Andreasen, and J. M. Pijanowski, “Structural Stator Spacers-the Key to Silent Electrical Machines,” Thirty-Sixth IAS Annu. Meet. Conf. Rec. 2001 IEEE Ind. Appl. Conf., vol. 1, no. C, pp. 33–39, 2001.

[Masoudi2013] K. Masoudi, M. R. Feyzi, and A. Masoudi, “Reduction of Vibration and Acoustic Noise in the Switched Reluctance Motor by Using New Improved Stator Yoke Shape,” in 2013 21st Iranian Conference on Electrical Engineering (ICEE), 2013, pp. 1–4.

[Pellery2012] Pellerey, P., “Etude et Optimisation du Comportement Vibro-Acoustique des Machines Electriques, Application au Domaine Automobile”, PhD thesis, Université de Technologie de Compiègne, Compiègne, France, 2012

[LeBesnerais2016] J. Le Besnerais, "Fast prediction of variable-speed acoustic noise due to magnetic forces in electrical machines," 2016 XXII International Conference on Electrical Machines (ICEM), Lausanne, 2016, pp. 2259-2265. doi: 10.1109/ICELMACH.2016.7732836

[Peters2011] S. Peters and F. Hetemi, « Airborne Sound of Electrical Machines using Symmetric Matrices in ANSYS 14”, ANSYS Conference

Documents

NOISE AND VIBRATIONS IN ELECTRIC MACHINES - … · 2017-11-20 · NOISE AND VIBRATIONS IN ELECTRIC MACHINES ... • New topologies with higher Noise, Vibration, Harshness (NVH)