NOISE AND VIBRATIONS IN ELECTRIC MACHINES

Transcription

1 NOISE AND VIBRATIONS IN ELECTRIC MACHINES Review of NVH sources & mitigation of electromagnetically-excited noise LE BESNERAIS Jean REGNIEZ Margaux 21 th September

2 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 2

3 SERVICES & PRODUCTS 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 vibroacoustic design optimization of electric machines EOMYS can be involved both at design stage & after manufacturing of electric machines 3

4 WEBINAR SUMMARY INTRODUCTION REVIEW OF NOISE & VIBRATIONS IN ELECTRIC MACHINES FOCUS ON MAGNETIC NOISE AND VIBRATION MITIGATION MODELING & SIMULATION OF ELECTROMAGNETICALLY-EXCITED NOISE CONCLUSION 4

5 Why vibro-acoustics are important when designing electrical machines? Importance of noise & vibration analysis 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 5

6 Review of noise sources in electric machines Noise of an electric traction machine during starting: mechanical sources (e.g. bearings, gearbox) aerodynamic sources (e.g. fans) electromagnetic sources (e.g. slot/magnet) 6

7 Mechanical noise and vibration sources Contributors to mechanical noise [Bertolini2012] Bearings Shaft imbalance Shaft eccentricity Sliding contacts - between rotor and bearings - slip rings - metal or carbon brushes Geared power transmission motor coupling Tightening fault 7

8 Bearing noise and vibrations [Momono1999] [Sterling2009] Causes of mechanical 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 Rotor response orbit (oil whirl) Rotor response orbit (inner & outer oil whirl) Noise depends on and can be modified by - Running speed - Load - Temperature - Alignment fault 8

9 Bearing noise and vibrations [Sterling2009] 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 Excessive unbalance Rotor misalignment Contact rub between rotor and bearings 9

10 Bearing noise and vibrations [Vijayraghavan1999] [Momono1999] [Augeix] Frequency content Ball bearings Structural fault - 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 Handling - Flaw noise - Contamination noise (due to dirt) 10

11 Bearing noise and vibrations [Vijayraghavan1999] [Tillema2003] 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 11

12 Aerodynamic noise and vibration sources Causes of aerodynamic noise and vibrations Acoustic radiation Natural convection Air flow in electrical machine (high speed) centrifugal fan Cooling system - air (fan) Shaftmounted fan Forced convection -> fan rotating with electrical machine - water - oil -> fan rotating independently -> external pump -> fluid flow and interaction with obstacles [Guédel] [Parrang2016] [Vijayraghavan1999] Examples of water jackets, from [Satrustegui2017] 12

13 Aerodynamic noise and vibrations [Guédel] [Parrang2016] [Vijayraghavan1999] Frequency content 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 Air stream velocity (m/s) Diameter of the fan (m) - Fan blades frequency: - Cooling air passing through rotor ducts frequency:!" #! Rotation speed (RPM) Number of blades Rotation speed (RPM) Number of rotor slots 13

14 Aerodynamic noise and vibrations Aerodynamic noise mitigation [Vad2014] [Wang2016] [Vijayraghavan1999] [Mizuno2013] 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 Example of texture, from [Wang2016] 14

15 Electromagnetic noise and vibration sources 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) Magnetostriction forces [Laftman 1995] see video at Maxwell / reluctance forces 15

16 Electromagnetic noise and vibration sources 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 exciting forces with stator/rotor structural modes Noise harmonic analysis of a PMSM with MANATEE software resonance 16

17 Electromagnetic noise and vibrations Frequency content 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 $%&" $ '$ ( ) * 0,+2 - $%&" #! # $ 0,+2. r=0 r=+/-1 r=+/2 s slip f s fundamental electrical frequency p pole pair number Ex: Z s =36 Z r =28 p=3 -> an excitation of wavenumber r=-2= occurs at f s (Z r /p+2) Slotting effect in permanent magnet synchronous machines mainly occur at $%&" 2/ 0 $ - $%&" 012 # $, # $,2. / # $ u 0 minimum positive integer v 0 relative integer GCD=Greatest Common Divider Ex: Z s =12 p=5 GCD=2= 1*10-1*12 -> u 0 =1, first excitation with r=2 occurs at 2x1f s = 2f s GCD=2= 5*10-4*12 -> u=5, another excitation with r=2 occurs at 2x5f s =10f s GCD=2= 7*10-6*12 -> u=7, another excitation with r=2 occurs at 2x7f s = 14f s 17

18 Electromagnetic noise and vibrations Frequency content General pattern of harmonic forces in PMSM open-circuit conditions GCD=Greatest Common Divider LCM=Least Common Multiple M c =GCD(Z s,2p) N c =LCM(Z s,2p) N c M c =Z s 2p Wavenumbers r r=2mc n=2 r=mc n=1 Wavenumber spacing =GCD(Z s,2p) -N c f s /p 2(u 0 -Zs/Mc)f s r=0 2u 0 f s 4u 0 f s N c f s /p Frequency spacing= LCM(Z s,2p)f R 2(u 0 +Zs/Mc)f s 2(2u 0 +Zs/Mc)f s 2N c f s /p 2(u 0 +2Zs/Mc)f s n=0 Frequency f r=0 cogging torque/pulsating radial force other radial & tangential force harmonics 18

19 Electromagnetic noise and vibrations Transfer path analysis Wavenumber Force direction Transfer path Description r>0 Radial, tangential Air borne Radial circumferential deflection of the outer stator yoke and frame or outer rotor (rotating in forced regime, pulsating at resonance) r=0 Radial Air borne Radial pulsating circumferential deflection of the stator yoke and frame or outer rotor r=0 Tangential (cogging torque / torque ripple) r=0 Tangential (cogging torque / torque ripple) Structural borne Air borne Propagation of rotor torsional vibration to rotor shaft line and gearbox mount, or bearing sleeves and outer stator frame Deflection of the outer stator yoke and frame or outer rotor following a unbalanced torsional mode due to particular boundary conditions r=1 Radial (unbalance magnetic pull) r=1 Radial (unbalance magnetic pull) Air borne Structural borne Bending / tilting deflection of the outer stator frame or outer rotor, in particular in clamped-free conditions Propagation of rotor bending vibration to rotor shaft line and gearbox mount, or bearing sleeves and outer stator frame Axial Air borne Axial deflection of the end-shields 19

20 Electromagnetic noise and vibrations 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 rotor slot number on maximum noise of an induction motor using MANATEE software Effect of stator roundness on variable speed sound level using MANATEE software (left: circular stator, right: elliptical stator shape) 20

21 Electromagnetic noise and vibrations Magnetic noise mitigation (magnetics) Skewing Pole shaping Modulation of pole width / position Modulation of slot width / position Notches Flux barriers Airgap increase Example of stepped-skew PMSM rotor Effect of a PMSM rotor skew angle on acoustic noise (MANATEE software) Use of rotor notch to mitigate acoustic noise (MANATEE software) 21

22 Electromagnetic noise and vibrations Magnetic noise mitigation (control) Spread spectrum switching strategies Harmonic current injection Load angle Magnetic noise mitigation (structural) Effect of harmonic current injection on noise level (MANATEE software) Lamination geometry (static + natural frequencies) Damping Coupling between housing & lamination Structural spacers Frequency [Hz] Frequency variation of m=0 mode [Rasmussen2001] [Masoudi2013] Stator yoke [mm] Effect of yoke height change on breathing mode natural frequency (MANATEE software) 22

23 Modelling and simulation of electromagnetic noise & vibrations Overall simulation workflow (weak coupling) ELECTRICAL MODEL Output: rotor & stator currents ELECTROMAGNETIC MODEL Output: time and space distribution of radial & tangential airgap flux density STRUCTURAL MODEL Output: radial vibration of the outer surface ACOUSTIC MODEL Output: acoustic noise spectrum Analytical Numerical Analytical PWM generation Extended equivalent circuits Saturation coefficient Circuit simulation (ODE) Analytical Numerical Permeance / mmf winding function Subdomain models Complex permeance Conformal mapping Non linear electromagnetic FEM Analytical 2D equivalent shell deflections 2D/3D natural frequencies with tooth correction factors Green s function for the vibration response SEA Analytical Semianalytical Semianalytical Semianalytical Numerical Equivalent radiation efficiency Dipole field expansion SEA Acoustic FEM/BEM strong circuit coupling Numerical Structural FEM Fully analytical Fully numerical Hybrid (preferred) 23

24 Available electromagnetic NVH simulation software VWP Virtual Work Principle MT Maxwell Tensor 24

25 Available electromagnetic NVH simulation software 25

26 Available electromagnetic NVH simulation software 26

27 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 27

28 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 interharmonics (continuous sound spectrum Vs discrete excitations) Missing validation of magnetic force calculation & mesh to mesh projection techniques [Magnet website] [Pellery2012] [LeBesnerais2016] [Peters2011] 28

29 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 electromagnetic methods in MANATEE software (left: SPMSM, right: SCIM) Use of finite element models (electromagnetics + structural mechanics) combined with Electromagnetic Vibration Synthesis algorithm in detailed mechanical design phase 29

30 Electromagnetic Vibration Synthesis (from MANATEE software) ELECTROMAGNETIC MODEL 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) Unit harmonic loads for wavenumbers r=0, ±2, ±4 3D airgap flux distribution r=0 HARMONIC FORCE PROJECTION r=2 r=3 Tangential and radial harmonic magnetic forces (magnitude, wavenumber, frequency, phase) Complex FRFs (radial & tangential) for each wavenumber r ELECTROMAGNETIC VIBRATION SYNTHESIS Torque/speed curve (variable speed control law) SPECTROGRAM SYNTHESIS STRUCTURAL MODEL STRUCTURAL FREQUENCY RESPONSE FUNCTIONS 3D external FEA software (Optistruct, Ansys) Manatee 2,5D analytic model Manatee numerical model (GetDP) r=0 r=2 Vibration and noise spectrograms Operational Deflection Shapes Modal contribution Radiating surface velocities 30

31 Examples of experimental validation with obtained with MANATEE software TESTS MANATEE -40 db Motor B Motor A Sound level during a run-up (experiments with gearbox+watercooling+converter harmonics) Sound level during a run-up (MANATEE simulation without converter harmonics) ~10 seconds on a laptop -> Semi-analytical models of MANATEE software can be successfully applied during first electromagnetic design loops, even when neglecting saturation and housing effect 31

32 Conclusions 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) 32

33 THANK YOU FOR YOUR ATTENTION Q&A SESSION For other EOMYS webinars, go to 33

34 REFERENCES [Vijayraghavan1999] P. Vijayraghavan, R. Krishnan, Noise in electric machines: a review, IEEE Transactions on Industry Applications 35(5), (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, [Vad2014] 228(3), [Parrang2016] Cachan, J. Vad et al., Aerodynamic and aero-acoustic improvement of electric motor cooling equipment, J. Power and Energy S. Parrang, Prédiction du niveau de bruit aéroacoustique d'une machine haute vitesse à reluctance variable, Thèse ENS [Mizuno2013] S. Mizuno et al., Development of a totally enclosed fan-cooled traction motor, IEEE Trans. Indus. Appl. 49(4),

35 REFERENCES [Sterling2009] J. Sterling, Influence of induced unbalance on subsynchronous vibrations of an automotive turbocharger, [Nguyen2015] H. Nguyen-Schäfer, Rotordynamics of automotive turbochargers, [Kirk2011] R.G. Kirk et al., Turbocharger vibration show nonlinear jump, JVC 18(10), [Kirk2010] R.G. Kirk et al., Turbocharger on-engine experimental vibration testing, JCV 16(3), [Kirk2006] R.G. Kirk et al., Stability analysis of a high speed automotive turbocharger, IJTC [Ishida2012] Y. Ishida and T. Yamamoto, Linear and nonlinear rotordynamics, Wiley [Bekemans2006] M. Bekemans, Modélisation des machines électriques en vue du contrôle des efforts radiaux, PhD thesis, UCL, [Tillema2003] H.G. Tillema, Noise reduction of rotating machinery by viscoelastic bearing supports, PhD thesis, Twente University, [Vijayraghavan1999] P. Vijayraghavan, R. Krishnan, Noise in electric machines: a review, IEEE Transactions on Industry Applications 35(5), [Momono1999] T. Momono and B. Noda, Sound and Vibration in Rolling bearings, Motion & Control 6, [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,

36 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 IEEE Ind. Appl. Conf., vol. 1, no. C, pp , [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 st Iranian Conference on Electrical Engineering (ICEE), 2013, pp [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 doi: /ICELMACH [Peters2011] Conference S. Peters and F. Hetemi, «Airborne Sound of Electrical Machines using Symmetric Matrices in ANSYS 14, ANSYS 36