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Originally Posted by e*clipse
This is one of the reasons I'm interested in SiC switches. The motors I'm using can run up to about 12,000 or maybe 13,000 rpm. I'd like to make use of their capabilities like this. 
It seems one would also want to increase the switching frequency to have good resolution at those speeds. Perhaps a motor speed adjustable switching frequency?? |
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The nice thing about the dspics is you can change the switching freqency every stinking cycle and it doesn't mind one bit. The only concern I would have is the code would have to run a tiny bit slower, since I optimized a few things to 10KHz, so as to avoid doing a couple integer divisions, which take 17 clock cycles. But if I still have a lot of room at 14MHz. And then have tons of room at 28MHz
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Switching frequency discussion - just so I can follow along:
- a higher dsPIC frequency means more computation, better control
- higher dsPIC frequency may mean higher A/D frequency to keep the control algorithmn fed with good data
- a higher switching frequency means higher losses, but better control, maybe need SiC transistors?
- lower switching frequency means lower losses, maybe a lower max speed?
10,000 rpm on a 50 Hz, 1500 rpm motor (2 pairs of poles, like the Siemens) would be running at 330 Hz or so. 10 Khz A/D would be 600,000 samples per minute, 60 samples per revolution, right?
Is there an issue with only 60 samples, or perhaps that MAY not be enough samples?
I think that the loop may already be too fast. If the acceleration I saw with the motor 'hunting' during the rotor test is typical - 30+ amps on one meter update (about 1 sec) and -something on the next meter update ... and the meter averages a bunch to get a relatively stable display number, I think that mechanical parts of the car would be very stressed. Acceleration from 0 speed to 2500 rpm can take 1 or 2 seconds if you are not racing. That's comparable to a performance engine, right?