Electromagnetic Force Coupling in Electric Machines Mark Solveson, Cheta Rathod, Mike Hebbes, Gunjan Verma, Tushar Sambharam ANSYS, Inc.

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1 Electromagnetic Force Coupling in Electric Machines Mark Solveson, Cheta Rathod, Mike Hebbes, Gunjan Verma, Tushar Sambharam ANSYS, Inc. 1 ANSYS, Inc. September 29,

2 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 2 ANSYS, Inc. September 29,

3 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 3 ANSYS, Inc. September 29,

4 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 4 ANSYS, Inc. September 29,

5 Noise Sources [1] Magnetic Mechanical Aerodynamic Electronic Radial Fluid Cooling Phenomena Switching Harmonics Slot Harmonics Self Auxiliaries Load Induced Magnetic Unbalance Stator Rotor Couplings Modes of Vibration Bearings Balancing Static Eccentricity Foundation Audible Frequencies Dynamic Eccentricity Elliptical Rotor Surface Unbalanced Rotor 20 Hz 60 Hz Hz 4.186kHz 5 khz 20 khz 5 ANSYS, Inc. September 29, [1] P. Vigayraghavan, R. Krishnan, Noise in Electric Machines: A Review, IEEE, 1998

6 ANSYS Machine Model 6 ANSYS, Inc. September 29,

7 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 Simplorer. 7 ANSYS, Inc. September 29,

8 V V V V V V ANSOFT Curve Info SINE1.VAL TR SINE2.VAL TR SINE3.VAL TR TRIANG1.VAL TR Machine Model in Maxwell - Simplorer 2D IPM (Interior Permanent Magnet) motor model created from RMxprt and Maxwell UDP (User Defined Primitive) for rotor Model V Model DModel1 SModel1 4 pole, 1500 RPM, 220 Volt DC bus. Two Control Strategies used: 6 step inverter In Maxwell PWM current regulated Cosimulation Maxwell with Simplorer + 110V LabelID=V V LabelID=V33 - D40 S_46 D34 D35 D41 S_47 D42 S_48 D36 D37 D43 S_49 D44 S_50 D38 D39 D45 LabelID=VIA H*Kle LA LabelID=VIB H*Kle LB LabelID=VIC H*Kle LC ohm RA ohm RB ohm RC LPhaseA LPhaseB LPhaseC LabelID=IVc1 LabelID=IVc2 LabelID=IVc3 LabelID=IVc4 LabelID=IVc5 LabelID=IVc6 S_51 100ohm 100ohm 100ohm 100ohm 100ohm 100ohm R20 R21 R22 R23 R24 R V LabelID=V V LabelID=V V LabelID=V V LabelID=V V LabelID=V V LabelID=V Sine Triangle Basic_Inverter Y ANSYS, Inc. September 29, Time [ms]

9 ANSOFT ANSOFT Machine Model in Maxwell - Simplorer SAS IP, Inc Torque Basic_Inverter1 SAS IP, Inc Currents Basic_Inverter1 Curve Info FEA1.TORQUE TR Curve Info RphaseA.I TR RphaseB.I TR RphaseC.I TR FEA1.TORQUE 7.50 Y1 [A] Time [ms] Time [ms] 9 ANSYS, Inc. September 29,

10 Force Calculations Force calculation using air gap flux density Maxwell Stress Tensor 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 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) 10 ANSYS, Inc. September 29,

11 Edge Force Density in Maxwell Tangential Force on Tooth Tips 02_DC-6step_IPM ANSOFT Force (Newtons) Curve Info ExprCache(ToothTipTangent_Full1) ExprCache(ToothTipTangent_2) ExprCache(ToothTipTangent_3) ExprCache(ToothTipTangent_4) ExprCache(ToothTipTangent_5) ExprCache(ToothTipTangent_6) Time [ms] Radial Force on Tooth Tips 02_DC-6step_IPM ANSOFT Force (Newtons) Curve Info ExprCache(ToothTipRadial_Full1) ExprCache(ToothTipRadial_2) ExprCache(ToothTipRadial_3) ExprCache(ToothTipRadial_4) ExprCache(ToothTipRadial_5) ExprCache(ToothTipRadial_6) Time [ms] 11 ANSYS, Inc. September 29,

12 Eccentricity Model Left Side Tooth Right Side Tooth 12 ANSYS, Inc. September 29,

13 Rotor missaligned 0%, 25%, 50% Parametric Study of Eccentricity Electromagetic Force Solved simultaneously on multi-core computer Shown: Radial Force on Right Tooth Tip FFT of Radial Force 13 ANSYS, Inc. September 29,

14 Edge Force Density, 50% Eccentricity 14 ANSYS, Inc. September 29,

15 50% Eccentricity: Radial and Tangential Force on Right Side and Left Side Tooth 0.00 Radial Tooth Tip Forces ANSOFT Tangential Tooth Tip Forces ANSOFT Force (N) Force (N) Curve Info Radial Force Small Gap Radial Force Large Gap Time [ms] Curve Info Tangential Force Small Gap Tangential Force Large Gap Time [ms] ANSYS, Inc. September 29,

16 ANSYS Force Mapping 16 ANSYS, Inc. September 29,

17 Two Approaches Direct Force Mapping Electromagnetic forces from Maxwell to Mechanical by linking systems in Workbench 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 17 ANSYS, Inc. September 29,

18 Approach 1 - Direct Force Mapping Scenario: Study the effect of Rotor Eccentricity Case 1: 0% Eccentricity No misalignment Case 2: 50 % Eccentricity Eccentricity amount is set to 50% of gap width Creates unbalanced electromagnetic forces Peak Edge Force Density 1.5e6 N/m 2 18 ANSYS, Inc. September 29, Peak Edge Force Density 1.9e6 N/m 2

19 Directional Deformation Radial Max Deformation vs time Case 1 0% Eccentricity 19 ANSYS, Inc. September 29, Case 2 50 % Eccentricity

20 Von Misses Stress Max Stresses vs time Case 1 0% Eccentricity 20 ANSYS, Inc. September 29, Case 2 50 % Eccentricity

21 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 21 ANSYS, Inc. September 29,

22 Approach 2 Lumped Force Mapping Electromagnetic Forces Export forces Workbench Flow Chart for Noise Prediction ANSYS Maxwell ANSYS Mechanical ANSYS Acoustics Lumped Forces in Time Domain Real/Imaginary Forces In Frequency Domain Harmonic Response Extract Acoustic Pressures Perform FFT in Maxwell APDL in Workbench APDL in Workbench 22 ANSYS, Inc. September 29,

23 ANSYS Harmonic Analysis 23 ANSYS, Inc. September 29,

24 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 24 ANSYS, Inc. September 29, Mode #4, 9080 Hz

25 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 (by using dampers, for example) To determine Acoustic response Boundary Conditions Input Forces Appling harmonic forces from Maxwell into ANSYS Mechanical 25 ANSYS, Inc. September 29,

26 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 26 ANSYS, Inc. September 29,

27 Harmonic Response Contour plot Amplitude distribution of the displacements at a specific frequency, Deformation plot at 8710 Hz 27 ANSYS, Inc. September 29,

28 ANSYS Acoustics 28 ANSYS, Inc. September 29,

29 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) 29 ANSYS, Inc. September 29,

30 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 30 ANSYS, Inc. September 29,

31 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-ACTRAN) 31 ANSYS, Inc. September 29,

32 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. 32 ANSYS, Inc. September 29,

33 Acoustic Analysis Pressure Plot 33 ANSYS, Inc. September 29,

34 Acoustic Analysis Pressure Plot 0.5 m Pres_1 Pres_2 Pres_3 Pressure vs Freq Pressure (Pa) 34 ANSYS, Inc. September 29, Freq(Hz)

35 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 35 ANSYS, Inc. September 29,

36 References P. Vijayraghavan, R. Krishnan, Noise in electric machines: A Review, IEEE, 1998 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,. S. Fink, S. Peters, Anosft - Noise Prediction for Electrical Motors, CADFEM/ANSYS Presentation,. 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. R. Belmans, D. Verdyck, W. Geysen, R. Findlay, Electro-Mechanical Analysis of the Audible Noise of an Inverter-Fed Squirrel-Cage Induction Motor, IEEE, M. Anwar, I. Husain, Design Perspectives of a Low Acoustic Noise Switched Reluctance Machine, IEEE, S. Huang, M. Aydin, T.A. Lipo, Electronmagnetic Vibration and Noise Assessment for Surface Mounted PM Machines, IEEE, Rakib Islam, Iqbal Hussain, Analytical Model for Predicting Noise and Vibration in Permanent Magnet Synchronous Motors, IEEE Pragasen Pillay, William (Wei) Cai, An Investigation into Vibration in Switched Reluctance Motors, IEEE Transactions on Industry Applications, Vol. 35, NO. 3, May/June/ ANSYS, Inc. September 29,

37 Thank You 37 ANSYS, Inc. September 29,