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Old 11-30-2009, 01:13 AM   #101 (permalink)
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Paul, I'm still stuck on the fancy encoder. Does it tell you absolute shaft position @ 0 RPM or how does it get things moving?

Mike, re: boost converters, I can't make %100 sense out of it from a purely efficiency standpoint. Don't know why Prius is using it exactly, but they are gas powered and might be able to trade some electrical efficiency for weight/cost.

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Old 11-30-2009, 01:47 AM   #102 (permalink)
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Hey DCB! It doesn't tell you absolute position. To do field oriented control, you need 2 of the currents in the 3 phases, and the rotor flux angle.

In a PMSM motor, the rotor flux angle is the same as the rotor angle. Unfortunately, in a AC induction motor, there are no permanent magnets, and the rotors magnetic field is induced by the current in the stator. The rotor angle lags behind the rotor flux angle.

The rotor flux angle is truly horrible to compute.
You need the following variables. Well, you are trying to solve for θ.

Imr = Magnetizing current (as calculated from measured values)
fs = Flux speed (as calculated from measured values)
T = Sample (loop) time (parameter in program)
n = Rotor speed (measured with the shaft encoder)
Tr = Lr/Rr = Rotor time constant (must be obtained from the motor manufacturer)
θ = Rotor flux position
ωb = Electrical nominal flux speed (from motor name plate)
Ppr = Number of pole pairs (from motor name plate)

See Pg. 4 for computing the rotor flux angle:
http://ww1.microchip.com/downloads/e...tes/00908B.pdf
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Old 11-30-2009, 12:54 PM   #103 (permalink)
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Mike (Paul, anyone) found interesting resource from department of energy on boost converters in the prius
Information Bridge: DOE Scientific and Technical Information - Sponsored by OSTI

page 36(45) has boost converter efficiency graph, previous page has motor/inverter efficiency graphs. Boost converter looks like about 3% loss at high voltages/loads (20kw), which might be acceptable considering battery/motor costs and availability.
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Old 11-30-2009, 07:42 PM   #104 (permalink)
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Quote:
Originally Posted by Christ View Post
The ABS sensor setup is a laser with a sprocket-like rotor.
No, it is a Hall effect sensor. Put a Volt meter on it and wave a piece of steel in front, you'll see pluses. The reason they need to be cleaned is that they collect Iron filings (Byproduct of Brake pads wearing on the Rotor) and throw off the magnetic field.

That said I see no reason that Hall effect sensor couldn't be used (unless they would be thrown off by the Magnetic (flux???) thrown off by the motor. They have 1/10th Degree Resolution on many engines when used as Cam, or Crank position sensors. They are cheap, easy to find, and pretty reliable.
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Old 11-30-2009, 09:15 PM   #105 (permalink)
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Covered that correction, must've forgot to edit the post. I had (incorrectly) assumed that because of the need for cleaning.
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Old 12-01-2009, 04:22 AM   #106 (permalink)
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I wonder if anyone has ever stamped out an inductive rotor for, say, a delco alternator?

I don't get the feeling that just shorting the field leads cuts it.

http://www.midwesternmedicalmachine....ild/index.html
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Old 12-01-2009, 07:47 AM   #107 (permalink)
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Quote:
Originally Posted by dremd View Post
That said I see no reason that Hall effect sensor couldn't be used (unless they would be thrown off by the Magnetic (flux???) thrown off by the motor.
I don't think they are, as I have hall effect sensors inside my bike hub motor in the magnetic field (its a brushless though not an AC), but regardless i'm fairly sure its not a static field.
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Old 12-01-2009, 09:39 AM   #108 (permalink)
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the rotor is not inherently magnetic though. The BLDCs seem to put the halls next to existing moving permanent magnets. With the wibbly wobbly flux angle in an induction motor, the hall effect might not have a good point of reference

...or a hall effect might actually be useful in measuring flux angle, when combined with rotor position detection.
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Old 12-01-2009, 10:04 AM   #109 (permalink)
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Quote:
Originally Posted by dcb View Post
the rotor is not inherently magnetic though. The BLDCs seem to put the halls next to existing moving permanent magnets. With the wibbly wobbly flux angle in an induction motor, the hall effect might not have a good point of reference

...or a hall effect might actually be useful in measuring flux angle, when combined with rotor position detection.
Well, since the hall sensor actually detects the change in the magnetic field at worst you get to divide the pulses from it with three if it gets confused by the AC motor...
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Old 12-01-2009, 03:57 PM   #110 (permalink)
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May be worth having a bit of hardware in there that physically prevents any two high and low side igbts on the same phase from turning on due to a glitch or something.

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