EcoModder Forum Paul and Sabrina's Cheap 3 Phase Inverter (AC Controller) with Field Oriented Control

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 11-30-2009, 01:13 AM #101 (permalink) needs more cowbell     Join Date: Feb 2008 Location: ÿ Posts: 5,038 pimp mobile - '81 suzuki gs 250 t 90 day: 96.29 mpg (US) schnitzel - '01 Volkswagen Golf TDI 90 day: 53.56 mpg (US) Thanks: 158 Thanked 269 Times in 212 Posts 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. __________________ WINDMILLS DO NOT WORK THAT WAY!!!
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 11-30-2009, 01:47 AM #102 (permalink) PaulH     Join Date: Feb 2008 Location: Maricopa, AZ (sort of. Actually outside of town) Posts: 3,832 Michael's Electric Beetle - '71 Volkswagen Superbeetle 500000 Thanks: 1,368 Thanked 1,202 Times in 765 Posts 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 __________________ kits and boards
 The Following 3 Users Say Thank You to MPaulHolmes For This Useful Post: dcb (11-30-2009), dremd (11-30-2009), mrbigh (11-30-2009)
 11-30-2009, 12:54 PM #103 (permalink) needs more cowbell     Join Date: Feb 2008 Location: ÿ Posts: 5,038 pimp mobile - '81 suzuki gs 250 t 90 day: 96.29 mpg (US) schnitzel - '01 Volkswagen Golf TDI 90 day: 53.56 mpg (US) Thanks: 158 Thanked 269 Times in 212 Posts 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. __________________ WINDMILLS DO NOT WORK THAT WAY!!! Last edited by dcb; 11-30-2009 at 01:36 PM..
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 Originally Posted by Christ 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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 The Following User Says Thank You to dremd For This Useful Post: Christ (11-30-2009)
 11-30-2009, 09:15 PM #105 (permalink) Moderate your Moderation.   Join Date: Nov 2008 Location: Troy, Pa. Posts: 8,919 Pasta - '96 Volkswagen Passat TDi 90 day: 45.22 mpg (US) Thanks: 1,369 Thanked 430 Times in 353 Posts Covered that correction, must've forgot to edit the post. I had (incorrectly) assumed that because of the need for cleaning. __________________ "¿ʞɐǝɹɟ ɐ ǝɹ,noʎ uǝɥʍ 'ʇı ʇ,usı 'ʎlǝuol s,ʇı"
 12-01-2009, 04:22 AM #106 (permalink) needs more cowbell     Join Date: Feb 2008 Location: ÿ Posts: 5,038 pimp mobile - '81 suzuki gs 250 t 90 day: 96.29 mpg (US) schnitzel - '01 Volkswagen Golf TDI 90 day: 53.56 mpg (US) Thanks: 158 Thanked 269 Times in 212 Posts 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 __________________ WINDMILLS DO NOT WORK THAT WAY!!!
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Quote:
 Originally Posted by dremd 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.

 12-01-2009, 09:39 AM #108 (permalink) needs more cowbell     Join Date: Feb 2008 Location: ÿ Posts: 5,038 pimp mobile - '81 suzuki gs 250 t 90 day: 96.29 mpg (US) schnitzel - '01 Volkswagen Golf TDI 90 day: 53.56 mpg (US) Thanks: 158 Thanked 269 Times in 212 Posts 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. __________________ WINDMILLS DO NOT WORK THAT WAY!!!
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Quote:
 Originally Posted by dcb 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...

 12-01-2009, 03:57 PM #110 (permalink) Master EcoModder     Join Date: Sep 2009 Location: Ireland Posts: 734 Thanks: 26 Thanked 304 Times in 171 Posts 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.