6.11s Notes for Lecture 2

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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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Faradays Law
So if a conductor is moving through a magnetic
field
Here is a cartoon of a DC commutator machine
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Key to operation is the Commutator Normal
Operation Poles Current paths Brushes Commutation
Brushes short current paths
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Operation of the PM machine
Here is a simple model Winding resistance added
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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
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Constant Voltage Operation
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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
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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
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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
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Analysis of permanent magnet operation uses a
load line, called Unit Permeance
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PM Commutator Machine Typical Configuration
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Expressions appropriate for surface magnet
commutator machines stolen from James Irelands
book
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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
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Surface Mount Magnet Synchronous Machine
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Voltage Analysis of the PM Synchronous Machine
Here is what magnetic flux density looks like,
vs. electrical angle
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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
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Phasing With respect to internal voltage
And with respect to terminal voltage
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Calculations Needed
Terminal voltage related to internal
voltage Synchronous Inductance Slot Leakage