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Helpful ReplyHot!I have problem with overflow of RPM Using AN1162(or AN1292, AN1078)

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Jin_sys
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2018/11/23 00:48:19 (permalink)
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I have problem with overflow of RPM Using AN1162(or AN1292, AN1078)

 
 
I'm working on making 54KW new motor Driver.
Motor spec is 3600RPM and 20 pole pair.
 
this is a big problem.
 
Program use RPM*pole pair. But!! In my application 3600*20=72000 and is over 32768(Q15 for 16bit).
So my motor is limit by 16bit, maximum speed that 32768/20 =1638.4RPM is under 3600RPM....
 
first, I try to predivision that mircrochip used. But there are so many assembly codes, it is not easy.
second, I try to change Unit PRM to RPS(=RPM/60) but it not works...
 
So, anyone solve this overflow problem?
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du00000001
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Re: I have problem with overflow of RPM Using AN1162(or AN1292, AN1078) 2018/11/23 01:45:35 (permalink) ☄ Helpfulby Jin_sys 2018/11/23 02:31:20
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The "trick" would be to divide all constants depending from omega by e.g. 4 and multiply all constants depending from 1/omega with 4.
This way you scale down omega by 4 (don't forget to correct the set value by 1/4 as well).
I can only guess that you missed the dependency on omega for the constants when trying to scale down from rpm to rps.
 
And no - I do not have a ready-made solution for you.
And don't forget: control quality will somewhat suffer: the control loop's frequency is 20 kHz and your pole frequency targeted is 1200 Hz - leaving not more than 16.5 cycles for each pole at max speed - not the best ratio to get a somewhat sinusoidal current.

PEBKAC / EBKAC / POBCAK / PICNIC (eventually see en.wikipedia.org)
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Jin_sys
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Re: I have problem with overflow of RPM Using AN1162(or AN1292, AN1078) 2018/11/23 02:39:22 (permalink)
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Oh I test for other ACIM, when I div RPM define, qVelEstimFilterK,Vel_Ref  by4 .
then give almost same speed.
Thank you.
 
And other 20pole motor, using fuji inverter, run 10khz PWM. manybe over 10Khz it is enough.
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du00000001
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Re: I have problem with overflow of RPM Using AN1162(or AN1292, AN1078) 2018/11/23 03:13:24 (permalink)
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10 kHz for a 20-pole (or pole-pairs?) motor?
At which max. RPMs? Certainly not 3600 - or not sinusoidal. (It would matter somewhat less when 6-step commutation is applied.)

PEBKAC / EBKAC / POBCAK / PICNIC (eventually see en.wikipedia.org)
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Jin_sys
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Re: I have problem with overflow of RPM Using AN1162(or AN1292, AN1078) 2018/11/23 04:01:40 (permalink)
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I was confused. It is 20 pole Motor.
RPM= 120*f/pole -> 3600=120*600/20
So, sin wave is 600Hz then PWM 10kHz is enough and fuji inverter run 20pole motor.
But not tested with our inverter.
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du00000001
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Re: I have problem with overflow of RPM Using AN1162(or AN1292, AN1078) 2018/11/23 05:39:31 (permalink)
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Nope (regarding your formula).
RPM (electrical) = RPM (mechanical) * number of pole pairs
Not sure about the mechanical RPMs for your 10 kHz motor: 1800 RPM (mech) ? (600 Hz sine?)
Then 16.66 control cycles per el. period is not really much, considering that a sine consists of 2 half-waves.

PEBKAC / EBKAC / POBCAK / PICNIC (eventually see en.wikipedia.org)
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Jin_sys
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Re: I have problem with overflow of RPM Using AN1162(or AN1292, AN1078) 2018/11/23 05:52:24 (permalink)
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mechanical RPM is 3600
And eletrical RPM is 3600*10 = 36000RPM=600 Hz
So sin wave is 600Hz then 10kHz/600=16.67 control cycle.
I understand what you are say.

But I have experiment result that fuji 10Khz PWM ACIM foc inverter run motor eletrical sin wave 500hz properly.(fuji inverter upper limit is 500hz)
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crosland
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Re: I have problem with overflow of RPM Using AN1162(or AN1292, AN1078) 2018/11/23 05:53:55 (permalink)
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Jin_sys
I was confused. It is 20 pole Motor.

You have told us that it is both 20 pole and 20 pole pair. The two terms are not interchangeable.
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du00000001
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Re: I have problem with overflow of RPM Using AN1162(or AN1292, AN1078) 2018/11/23 07:30:26 (permalink)
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Now we're down to 10 pole pairs and 500 Hz (making for 20 control cycles per el. revolution - a significant improvement over 16.6 cycles).

PEBKAC / EBKAC / POBCAK / PICNIC (eventually see en.wikipedia.org)
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Narendra
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Re: I have problem with overflow of RPM Using AN1162(or AN1292, AN1078) 2019/08/06 10:41:48 (permalink)
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Hi...
I have developed an ACIM drive and using AN1162 as reference for firmware development. The firmware provided with AN1162 is working fine for lower RPM (@3000). However, I want to use same for RPM upto 20000.
I am facing issues while setting higher speed. I am using variable 'ReadADCParm.qADValue' for setting speed.
In original firmware, this variable is right shifted by 3 (means divided by 8). Since I want to use same for higher RPM, I have right shifted it by 2. I am able to achieve higher RPM (upto 7000) with one motor. But not able to achieve higher RPM with other motor (with different parameters).
Can you help me in this regard?
Thanks in advance.
Narendra
 
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du00000001
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Re: I have problem with overflow of RPM Using AN1162(or AN1292, AN1078) 2019/08/06 11:34:07 (permalink)
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@ Narendra
Don't capture an existing thread sad - start your own !

PEBKAC / EBKAC / POBCAK / PICNIC (eventually see en.wikipedia.org)
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nigelwright7557
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Re: I have problem with overflow of RPM Using AN1162(or AN1292, AN1078) 2019/08/06 20:36:50 (permalink)
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Its not too difficult to change to 32 bits.
Just write some code to do add32, sub32, mpy32 and div32.
Input first number to 32 bit no_1, second number to 32 bit no_2 and have a 32 bit variable called anser for result of maths. Its hard work to write them all yourself but you should be able to find them online.
 
 
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