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6.11s Notes for Lecture 2 DC and PM ‘Brushless’ Machines June 12, 2006 J.L. Kirtley Jr.

6.11s Notes for Lecture 2 DC and PM ‘Brushless’ Machines June 12, 2006 J.L. Kirtley Jr. Faraday’s Law:. So if a conductor is moving through a magnetic field:. Here is a cartoon of a DC commutator machine. Key to operation is the Commutator Normal Operation Poles Current paths Brushes

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6.11s Notes for Lecture 2 DC and PM ‘Brushless’ Machines June 12, 2006 J.L. Kirtley Jr.

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  1. 6.11s Notes for Lecture 2 DC and PM ‘Brushless’ Machines June 12, 2006 J.L. Kirtley Jr.

  2. Faraday’s Law: So if a conductor is moving through a magnetic field: Here is a cartoon of a DC commutator machine

  3. Key to operation is the Commutator Normal Operation Poles Current paths Brushes Commutation Brushes short current paths

  4. Operation of the PM machine: Here is a simple model: Winding resistance added

  5. Operation of the PM machine: Here we have two separate voltage controls. This is separately excited operation and is very flexible. Some machines are wound so that the field and armature can be connected in series

  6. Constant Voltage Operation

  7. If we add inductance to the model we can build up a simulation model: You will have a chance to run some of these in the lab

  8. Permanent Magnets B-H Characteristic of modern ceramic material. Remanent Flux Density Coercive Field NdFeB magnets have numbers substantially larger: Remanent Flux Density can be as large as 1.4T

  9. If the demag curve has constant slope, max energy product is: We usually need only the second quadrant of the magnetization curve Energy Product isB(Gauss) X H(Oe) and is expressed in MGOe

  10. Analysis of permanent magnet operation uses a load line, called Unit Permeance

  11. PM Commutator Machine: Typical Configuration

  12. Expressions appropriate for surface magnet commutator machines stolen from James Ireland’s book:

  13. Voltage induced has this form. The angle is the lesser of armature coil throw or magnet angular width Number of effective conductors in series is related to that minumum angle Then the motor constant can be easily calculated. This motor is like one with constant field current

  14. Surface Mount Magnet Synchronous Machine

  15. Voltage Analysis of the PM Synchronous Machine Here is what magnetic flux density looks like, vs. electrical angle

  16. Magnetic field can be found through a little field analysis The result below is good for magnets inside and p not equal to one. See the notes for other expressions

  17. Phasing: With respect to internal voltage And with respect to terminal voltage:

  18. Calculations Needed Terminal voltage related to internal voltage Synchronous Inductance Slot Leakage

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