Just some info on the 2nd gen prius a/c compressors that I've either read about or figured out from playing with them:
They're 6 pole motors, so 3 electrical cycles per one physical cycle. I've seen specs that say max speed is 6000 rpm (100 Hz), so that'd be 300 Hz output from the inverter. I did see another document that said up to 7500 rpm. With my 144v nominal pack that rests close to 150V, max speed under load on hot days is about 4000 rpm. I've read that the prius pack voltage is around 200V, so maybe the 6000 rpm max speed is correct. The motor is also highly salient - that is, it's inductance is much higher in the q-axis (if i remember right). Reluctance torque can be generated with current along the d-axis and increase the overall torque per amp. The motor can run open loop - in fact, I do this in order to ramp the motor up to a minimum speed before the sensorless position algorithm takes over. But, running open loop will limit the max speed and decrease the torque per amp and overall efficiency. On Fri, Jun 12, 2015 at 8:45 AM, Lee Hart via EV <ev@lists.evdl.org> wrote: > Robert Bruninga via EV wrote: > >> 3 phase 60 Hz AC synchronous motors seem to start and run just fine >> on fixed 60 Hz frequency, why does one need to ramp up and have precise >> feedback of rotor position therefore frequency and phase to make a >> DC controller? >> > > Synchronous motors are rare on fixed 60Hz AC because they are hard to > start; and draw excessive current while trying to start. > > When you try to start it, the rotor tries to *instantly* move to the shaft > angle that corresponds to the phase of the applied AC at that instant. To > jump instantly from 0 to synchronous speed would require *infinite* torque > (0 to 60 in 0 seconds)! And that would require infinite current! Not gonna > happen. > > Of course, it can't draw infinite current; but starting current will be > very high. The torque will be correspondingly high; but is often still not > enough to jump the rotor from a dead stop up to synchronous speed in a > single cycle. The motor might lurch forward; or even *backward* (if that > happened to be the closest direction to make shaft position and AC > waveforms match). Or just sit there and vibrate, trying in vain to "catch" > one of the cars in that train of rapidly passing AC sinewaves. > > Also, once running, the synchronous motor needs to be wound so its back > EMF at synchronous RPM just happens to be the AC supply voltage. If the > supply voltage is high, the motor still runs but has a lagging power > factor. If the supply voltage is low, it has a leading power factor. Both > of these lead to increased I2R losses and thus poorer efficiency. > > Most fixed 60Hz AC synchronous motors are modified to reduce these > problem. Synchronous-hysteresis motors have no permanent magnets; but use a > "hard" magnetic rotor material that self-magnetizes once it's running (and > de-magnetizes when it stops). Synchronous-induction motors "bury" the > magnets inside a conventional induction rotor that is used to start the > motor. Or a wound-rotor synchronous motor, with slip rings so the field can > be controlled externally. > > That said... I do think there is hope for driving a true synchronous motor > with a simple square-wave DC inverter within limits. It will mainly be hard > to start, and you won't get peak efficiency. > > -- > The greatest pleasure in life is to create something that wasn't > there before. -- Roy Spence > -- > Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com > > _______________________________________________ > UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub > http://lists.evdl.org/listinfo.cgi/ev-evdl.org > For EV drag racing discussion, please use NEDRA ( > http://groups.yahoo.com/group/NEDRA) > > -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20150612/be28f586/attachment.htm> _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org For EV drag racing discussion, please use NEDRA (http://groups.yahoo.com/group/NEDRA)
