Three-Phase AC drive
yarisboy
Posts: 245
I've searched and searched, and searched the Propeller forums to find info on this subject with out success. How do I need to modify my search nouns to get a relevant hit? Is this subject verbotten? By modifying my search nouns on Google to "PWM code segments" I'm getting good hits on the dark side by Microchip hobby types. I did some calculations with a hand calculator to see if the Propeller could possibly keep up with processing demands for a high-carrier-speed PWM drive for three-phase motors. I suspect the biggest limitation is between my ears rather than in the design of the Propeller.
As I slog through the Propeller training drills flashing LEDs the how-to questions for PWM AC applications keep bouncing around in the back of my head. The dark-side hobby types have limited their number of outputs and carrier frequency to get around the limitations of a single processor. They typically limit the scope to DC drives and H drives for stepper motors just like the Parallax camp. Typical coping methods are: output buffers, extra post process chips, slower speeds, low phase count. interrupts, etc. I no doubt will hit a bandwidth limit with lab experiments written in Spin. How much faster could the usable carrier frequency get as more and more objects/methods are converted over to PSAM?
The white papers indicate that carrier frequencies above 20 KHz cause bearing failures due to high induced motor shaft currents. Do any of the inverter duty motors come with insulated shaft bearings? Yeh, I know about shaft brushes but I'm not going there. I'm checking into my possible access to MATLAB and LABVIEW resources at reasonable cost this week.
As I slog through the Propeller training drills flashing LEDs the how-to questions for PWM AC applications keep bouncing around in the back of my head. The dark-side hobby types have limited their number of outputs and carrier frequency to get around the limitations of a single processor. They typically limit the scope to DC drives and H drives for stepper motors just like the Parallax camp. Typical coping methods are: output buffers, extra post process chips, slower speeds, low phase count. interrupts, etc. I no doubt will hit a bandwidth limit with lab experiments written in Spin. How much faster could the usable carrier frequency get as more and more objects/methods are converted over to PSAM?
The white papers indicate that carrier frequencies above 20 KHz cause bearing failures due to high induced motor shaft currents. Do any of the inverter duty motors come with insulated shaft bearings? Yeh, I know about shaft brushes but I'm not going there. I'm checking into my possible access to MATLAB and LABVIEW resources at reasonable cost this week.
Comments
And as far as the Subject of three phase ac drive, ... some still don't get it.
The propeller can OUTPUT VIDEO DATA (this is high rate data)
And can input (sample) at a very high rate also. (but not as high as its output)
The dsp/fpga king is dead, long live the prop. [noparse];)[/noparse]
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In the later case, it seems that you really don't need to recreate a detailed sine wave. If i recall correctly, they do do in 3-4 steps from zero to full on.
It certainly would be interesting to make a Propeller into a combined ESC controller for RC and autopilot for the same R/C controlled airplane.
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Ain't gadetry a wonderful thing?
aka G. Herzog [noparse][[/noparse] 黃鶴 ] in Taiwan
Absolutely the right track! Microchip has excellent AppNotes with all the necessary theory behind and flowcharts and and and ...
Read them, get the theory and then do it on the Prop. The Prop certainly is fast enough.
**BUT** IIRC, this app involves ADC (for current sensing), and then you have to get running SPI or I2C fast enough for an external ADC.
Nick
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Never use force, just go for a bigger hammer!
The DIY Digital-Readout for mills, lathes etc.:
YADRO
One the one hand, Parallax has never had the deep pockets to write the tons of APP NOTEs that Microchip produces, but with Parallax you are nearly always able to find someone who will mentor you through a project if you are willing to listen and think. So both are excellent resources in their own way. I still prefer Parallax hardware as a few chips will do nearly anything. Microchip does everything hardware and has a vast and complicated product line.
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Ain't gadetry a wonderful thing?
aka G. Herzog [noparse][[/noparse] 黃鶴 ] in Taiwan
Post Edited (Loopy Byteloose) : 6/29/2009 2:19:13 AM GMT
Leon
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Amateur radio callsign: G1HSM
Suzuki SV1000S motorcycle
I'm writing this only, because it was me who wrote "you need a current sensor".
Before trusting me, better trust the literature.
Nick
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Never use force, just go for a bigger hammer!
The DIY Digital-Readout for mills, lathes etc.:
YADRO
Post Edited (yarisboy) : 7/3/2009 1:16:36 AM GMT