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# ANSYS: Simulation of a magnetic angle measurement system

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### ANSYS: Simulation of a magnetic angle measurement system

1. 1. Simulation of a magnetic anglemeasurement systemANSYS Conference & 7. CADFEM Austria User‘s Meeting 26. – 27. April 2012Gernot Binder
2. 2. Outline Problem description  Electrically commutated motor working principle  Sinusoidal commutation  Sinusoidal commutation using GMR angle sensor  Out of axis angle measurement Magnetic circuit simulations  Diametrically magnetized ring magnet  Pole wheels with different number of pole pairs  Nonius principle System simulations  Incorporating FEM results in the MATLAB Simulink model  Sensor Calibration Copyright © Infineon Technologies 2012. All rights reserved. Page 2
3. 3. EC motor working principle Three excitation coils on stator Diametrically magnetized permanent magnet on rotor No mechanical contact between stator and rotor  brushless Benefits ¬ No mechanical wear ¬ small rotor inertia Drawbacks ¬ Need for a rotor/shaft position feedback system for current commutation Copyright © Infineon Technologies 2012. All rights reserved. Page 3
4. 4. Sinusoidal commutation Three energized phases at a time Benefits of sinusoidal commutation:  Low torque ripple  high efficiency Rotor position has to be known with high accuracy 3 excitation currents shifted by 120° 1,2 1 0,8 0,6 Phase current 0,4 0,2 0 U -0,2 -0,4 V -0,6 -0,8 W -1 -1,2 0 100 200 300 reference angle Principle of a 3-phase driver stage and corresponding phase currents Copyright © Infineon Technologies 2012. All rights reserved. Page 4
5. 5. Sinusoidal commutation using GMR-based sensor Diametrically magnetized permanent magnet at the end of shaft GMR-based angle sensor placed in front of the shaft ¬ Two Wheatstone bridges oriented at 90° deliver sine and cosine signals. Angle is given by arc tangent of signal amplitude relation Benefits ¬ High resolution allows smooth torque control ¬ Only one angle sensor instead of three Hall switches required Copyright © Infineon Technologies 2012. All rights reserved. Page 5
6. 6. GMR-effect Giant Magneto Resistive effect Spin Valve Stack ¬ Two ferromagnetic layers divided by non-magnetic spacer layer ¬ Magnetization of free layer follows external magnetic field ¬ Resistance in spacer layer depends on magnetization orientation of the magnetic layers R R (1  cos m1m 2 ) (m1m 2 )  ( )GMR  R R 2 AAF Copyright © Infineon Technologies 2012. All rights reserved. Page 6
7. 7. Out of axis measurement End of shaft measurement not always possible Place sensor out of axis at the shaft circumference Problems occur:  Angle accuracy depends on: ¬ Number of pole pairs / Magnetic coding ¬ Shaft diameter ¬ Sensor distance Use ANSYS to design a magnetic circuit that delivers appropriate magnetic fields Use Matlab/Simulink for a combined system simulation (Magnetic circuit – GMR sensor – Integrated signal conditioning) Copyright © Infineon Technologies 2012. All rights reserved. Page 7
8. 8. Error sources ANSYS Matlab / Simulink Geometry Offsets Structure Phase shifts Magnetization Amplitudes Sensor location Temperature drifts Error compensation Overall angle error Magnetic Sensor circuit related related errors errors Copyright © Infineon Technologies 2012. All rights reserved. Page 8
9. 9. Magnetic analysis 90 0.02 120 60 400 0.02 measured angle ° Bx 0.015 300 0.015 By 0.01 200 150 30 0.01 100 magnetic flux density in T 0.005 0.005 0 0 50 100 150 200 250 300 350 400 0 180 0 reference angle ° 0.1 -0.005 0.05 angle error ° -0.01 210 330 0 -0.015 -0.05 -0.02 240 300 -0.1 0 50 100 150 200 250 300 350 400 0 50 100 150 200 250 300 350 400 reference angle in ° 270 reference angle ° 90 0.04 0.04 120 60 400 0.03 0.03 single pole wheel 2 poles 0.02 150 0.02 30 200 magnetic flux density in T 0.01 0.01 0 0 0 50 100 150 200 250 300 350 400 180 0 -0.01 50 angle error ° -0.02 210 330 0 -0.03 -0.04 -50 0 50 100 150 200 250 300 350 400 240 300 0 50 100 150 200 250 300 350 400 reference angle in ° 270 reference angle ° 90 0.04 0.04 120 60 400 Bx 0.03 By 0.03 single pole wheel 2 poles 0.02 150 0.02 30 200 magnetic flux density in T 0.01 0.01 0 0 50 100 150 200 250 300 350 400 0 180 0 50 -0.01 angle error ° -0.02 0 210 330 -0.03 -50 -0.04 240 300 0 50 100 150 200 250 300 350 400 0 50 100 150 200 250 300 350 400 reference angle in ° reference angle ° 270 Copyright © Infineon Technologies 2012. All rights reserved. Page 9
10. 10. Nonius principle By increasing the number of pole pairs, 400 single pole wheel 2 poles the error can be reduced 200 0 0 50 100 150 200 250 300 350 400  But measured angle is ambiguous 50 angle error ° over one shaft revolution 0 -50 0 50 100 150 200 250 300 350 400 reference angle ° By the Nonius principle unambiguity of angle over one shaft revolution is achieved 2 Sensors triggered by 2 pole wheels ¬ 1st pole wheel has x pole pairs ¬ 2nd pole wheel has x+1 pole pairs Output angle is calculated by subtracting the low-res angle of sensor 1 from the high-res angle of sensor 2 Copyright © Infineon Technologies 2012. All rights reserved. Page 10
11. 11. Result of the Nonius principle Maximum angle error is about +/- 0.07° (ideal magnetization) 400 measured angle ° 300 200 40 poles 100 38 poles output angle 0 0 50 100 150 200 250 300 350 400 reference angle ° 0.1 angle error 0.05 angle error ° 0 -0.05 -0.1 0 50 100 150 200 250 300 350 400 reference angle ° Copyright © Infineon Technologies 2012. All rights reserved. Page 11
12. 12. Design optimization How large is the influence of non-ideal magnetization?  Non-ideal magnetization: slightly varying pole widths ¬ Production related alternating width of adjacent poles (+/- 2.2 %)  Error increases to +/- 0.16° 400 measured angle ° 300 200 40 poles 100 38 poles output angle 0 0 50 100 150 200 250 300 350 400 reference angle ° 0.2 angle error 0.1 angle error ° 0 -0.1 -0.2 0 50 100 150 200 250 300 350 400 reference angle ° Copyright © Infineon Technologies 2012. All rights reserved. Page 12
13. 13. MATLAB Simulink model Influence of sensor electronics and signal processing is modeled using MATLAB Simulink B-field components obtained from FEM simulations are exported as *.txt-file Magnetic Circuit Sensor Related Errors Overall Related Errors Angle Error Copyright © Infineon Technologies 2012. All rights reserved. Page 13
14. 14. Incorporating FEM results Reference angle of shaft  Model of the Wheatstone serves as index for the bridge LUT  Angle is decomposed in From the entries in the sine and cosine component LUT the angle of the  Output voltages vary in magnetic field is amplitude, phase and calculated by the arc offset tangent function Copyright © Infineon Technologies 2012. All rights reserved. Page 14
15. 15. Sensor calibration techniques Dedicated algorithm implemented in the signal conditioning circuit to compensate for offsets, amplitudes, phase shifts and temperature drifts. Angle performance without Angle performance with parameter correction parameter correction Copyright © Infineon Technologies 2012. All rights reserved. Page 15
16. 16. Results before and after sensor calibration Output signals of GMR sensor without compensation measured angle angle error 0.08 deviation from reference angle 400 Vx 60 measured angle without parameter correction Simulink model Vy 0.06 350 40 300 0.04 250 20 measured angle in °Amplitude in V 0.02 Error in ° 200 0 0 150 -20 100 -0.02 50 -40 -0.04 0 -60 -0.06 -50 0 0.5 1 1.5 2 2.5 3 3.5 0 0.5 1 1.5 2 2.5 3 3.5 4 0 0.5 1 1.5 2 2.5 3 3.5 4 -3 time in seconds -3 time in seconds -3 x 10 x 10 x 10 Output signals after parameter correction 4 measured angle angle error x 10 2 deviation from reference angle 400 0.06 measured angle after parameter correction Simulink model 1.5 350 0.04 1 300 0.02 measured angle in ° Amplitude in digits 0.5 250 0 Error in ° 0 200 -0.02 -0.5 150 -0.04 -1 100 -0.06 -1.5 50 -0.08 -2 -0.1 0 0 0.5 1 1.5 2 2.5 3 3.5 4 0 0.5 1 1.5 2 2.5 3 3.5 4 0 0.5 1 1.5 2 2.5 3 3.5 4 -3 time in seconds -3 time in seconds -3 x 10 x 10 x 10 Copyright © Infineon Technologies 2012. All rights reserved. Page 16
17. 17. Thank you for your attention! References  Infineon Technologies AG. Position Feedback for Motor Control Using Magnetic Sensors. Infineon Technologies AG, 2010.  Infineon Technologies AG. TLE5012B GMR-Based Angular Sensor - Datasheet. Infineon Technologies AG, 2010.  Infineon Technologies AG. TLE5009 GMR-Based Angular Sensor - Application Note TLE5009 Calibration. Infineon Technologies AG, 2010. Copyright © Infineon Technologies 2012. All rights reserved. Page 17
18. 18. Appendix
19. 19. Process for obtaining simulation results (1) Ansys DesignModeler  Definition of: ¬ geometry of pole wheel ¬ coordinate systems for magnetization Copyright © Infineon Technologies 2012. All rights reserved. Page 19
20. 20. Process for obtaining simulation results (2) Ansys Mechanical  Definition of ¬ Materials ¬ Magnetization direction  Creating user defined results Copyright © Infineon Technologies 2012. All rights reserved. Page 20