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Massachusetts Institute of Technology Department of Electrical Engineering and Computer Science

Massachusetts Institute of Technology Department of Electrical Engineering and Computer Science 6.131 Power Electronics Laboratory Lecture 24 November 10, 2005. Coils are wound on a toroidal core ( a magnetic circuit). Axial View: Magnets are interacting with stator current.

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Massachusetts Institute of Technology Department of Electrical Engineering and Computer Science

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  1. Massachusetts Institute of Technology Department of Electrical Engineering and Computer Science 6.131 Power Electronics Laboratory Lecture 24 November 10, 2005 6.131 Lecture 24

  2. 6.131 Lecture 24

  3. 6.131 Lecture 24

  4. 6.131 Lecture 24

  5. 6.131 Lecture 24

  6. Coils are wound on a toroidal core ( a magnetic circuit) 6.131 Lecture 24

  7. Axial View: Magnets are interacting with stator current 6.131 Lecture 24

  8. Magnetic materials exhibit hysteresis For core materials you want a narrow curve But for PM materials you want a wide curve 6.131 Lecture 24

  9. Hard permanent magnet materials have B-H curves like this Remanent Flux density can be as high as 1.4 T Incremental permeability is like free space 6.131 Lecture 24

  10. Magnet Characteristic Geometry Combination 6.131 Lecture 24

  11. This graphic shows that calculation 6.131 Lecture 24

  12. Nomenclature: Two more views of the machine 6.131 Lecture 24

  13. This is a ‘cut’ from the radial direction (section BB) 6.131 Lecture 24

  14. Here is a cut through the machine (section AA) Winding goes around the core: looking at 1 turn 6.131 Lecture 24

  15. Voltage is induced by motion and magnetic field Induction is: Voltage induction rule: Note magnets must agree! 6.131 Lecture 24

  16. Single Phase Equivalent Circuit of the PM machine Ea is induced (‘speed’) voltage Inductance and resistance are as expected This is just one phase of three Voltage relates to flux: 6.131 Lecture 24

  17. PM Brushless DC Motor is a synchronous PM machine with an inverter: 6.131 Lecture 24

  18. Induced voltages are: Assume we drive with balanced currents: Then converted power is: Torque must be: 6.131 Lecture 24

  19. Now look at it from the torque point of view: 6.131 Lecture 24

  20. Terminal Currents look like this: So torque is, in terms of DC side current: 6.131 Lecture 24

  21. Rectified back voltage is max of all six line-line voltages Va Vc Vb <Eb> Vab 6.131 Lecture 24

  22. Average Rectified Back Voltage is: Power is simply: 6.131 Lecture 24

  23. So from the DC terminals this thing looks like the DC machine: 6.131 Lecture 24

  24. Magnets must match (north-north, south-south) for the two rotor disks. Looking at them they should look like this: End A End B Keyway 6.131 Lecture 24

  25. Need to sense position: Use a disk that looks like this 6.131 Lecture 24

  26. Position sensor looks at the disk: 1=‘white, 0=‘black’ 6.131 Lecture 24

  27. Some care is required in connecting to the position sensor Vcc GND Channel 1 Channel2 (you need to figure out which of these is ‘count’ and which is ‘zero’) 6.131 Lecture 24

  28. Control Logic: Replace open loop with position measurement 6.131 Lecture 24

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