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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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slide1

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

slide8

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

slide9

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

slide10

Magnet Characteristic

Geometry

Combination

6.131 Lecture 24

slide14

Here is a cut through the machine (section AA)

Winding goes around the core: looking at 1 turn

6.131 Lecture 24

slide15

Voltage is induced by motion and magnetic field

Induction is:

Voltage induction rule:

Note magnets must agree!

6.131 Lecture 24

slide16

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

slide18

Induced voltages are:

Assume we drive with balanced currents:

Then converted power is:

Torque must be:

6.131 Lecture 24

slide20

Terminal Currents look like this:

So torque is, in terms of DC side current:

6.131 Lecture 24

slide22

Average Rectified Back Voltage is:

Power is simply:

6.131 Lecture 24

slide24

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

slide27

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

slide28

Control Logic:

Replace open loop with position measurement

6.131 Lecture 24