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RESOLVED - Different values for PwmFreqMult
#1
Hi, I am operating a PowerBrickLV with 5/15A on all 8 Channels.
I am trying to find the optimal setup for our experiment with 7 motors.
I wanted to set different pwm-frequencies for the motors.
When I leave the multiplier for the motor the same, but change it for other motors
it affects the motor for which I have not changed it. Is that possible?

This works fine for motor on Chan[2]:

PowerBrick[0].Chan[0].PwmFreqMult = 1
PowerBrick[0].Chan[1].PwmFreqMult = 1
PowerBrick[0].Chan[2].PwmFreqMult = 1
PowerBrick[0].Chan[3].PwmFreqMult = 1
PowerBrick[1].Chan[0].PwmFreqMult = 1
PowerBrick[1].Chan[1].PwmFreqMult = 1
PowerBrick[1].Chan[2].PwmFreqMult = 1
PowerBrick[1].Chan[3].PwmFreqMult = 1

Now the same motor on Chan[2] doesn't work any more:

PowerBrick[0].Chan[0].PwmFreqMult = 1
PowerBrick[0].Chan[1].PwmFreqMult = 1
PowerBrick[0].Chan[2].PwmFreqMult = 1
PowerBrick[0].Chan[3].PwmFreqMult = 2
PowerBrick[1].Chan[0].PwmFreqMult = 2
PowerBrick[1].Chan[1].PwmFreqMult = 2
PowerBrick[1].Chan[2].PwmFreqMult = 1
PowerBrick[1].Chan[3].PwmFreqMult = 1

Any ideas or explanations?
Best,
hannsx
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#2
I am not sure what settings are before and after the change, but depending on your phase frequency those values look low. The 5/15 Power Brick LV has a minimum PWM Frequency of 20 kHz and 30 kHz is recommended.
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#3
Hi Eric, thank you for your response. I made a calculation error... I will check if that's the cause and label the matter as resolved till then.
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#4
Hello Eric

I may have misinterpreted it, but the manual recommends 20kHz and 30kHz is the maximum frequency.

Could you confirm if the recommended is 20kHz or 30kHz?

Thanks in advance.


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#5
Quote:I may have misinterpreted it, but the manual recommends 20kHz and 30kHz is the maximum frequency.

Could you confirm if the recommended is 20kHz or 30kHz?
Sorry I said it backwards. The manual is correct. 20 kHz is recommended, 30 is maximum.
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#6
Hi Eric, thank you. I never payed notice to that. So if I set the value to high I run into problems like that. So does the PowerBrick then actually try to accomodate for the the value I set and makes it cause electrical problems or does it kind of rollover into another value below 30kHz?
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#7
Hi Eric,
since I have your attention and you are the most knowledgeable man on these controllers, I would like to ask about the current-loop tuning.
I did not find another thread about it. I am often not able do tune the current-loop of small stepper motors apropriately with the tuning tools. In these cases I just go with trial and error. However I realize that this is far from ideal. My guess has been that it might be due to high impedances and bad wiring. But I wonder if you know anything about that problem in general and solutions to it,
best regards,
hannsx
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#8
hannsx Wrote:Hi Eric, thank you. I never payed notice to that. So if I set the value to high I run into problems like that. So does the PowerBrick then actually try to accomodate for the the value I set and makes it cause electrical problems or does it kind of rollover into another value below 30kHz?

The Gate3 inside the Power Brick will send an above 30 kHz signal to the amplifier, which may have issues due to the power transistors.

hannsx Wrote:I would like to ask about the current-loop tuning.
I did not find another thread about it. I am often not able do tune the current-loop of small stepper motors apropriately with the tuning tools. In these cases I just go with trial and error. However I realize that this is far from ideal. My guess has been that it might be due to high impedances and bad wiring. But I wonder if you know anything about that problem in general and solutions to it,

I am assuming you have already set BrickLV.Chan[j].TwoPhaseMode = 1 and then ran the Power On Reset PLC to apply it. I don't know of any tricks required for tuning current loop on stepper motors (Brushed need a couple). It may have to do with your resistance/inductance. If you use the equations in the Power Brick LV manual to calculate minimum PWM frequency for the motor, what do you get?

Are you using automatic or interactive current loop tuning? What goes wrong with it?
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#9
If the PWM Frequency is set too high, it could lead to an amplifier overcurrent fault (C on 7 segment display) or overheating.

What are your Phase and PWM clock frequencies?
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#10
Hi Eric, I am sorry for not having answered earlier. I just a minute ago found out what caused the problem when tuning the motors.
It is the routine for setting the hold-current of the motor. It runs in the phase routine of motor[0]. When we turn it of, the current-loop tuning is much easier and draws a nice graph in response. That has been a big problem for me and I am happy that we finally solved that. On the other hand we have not had the time to test different pwm-frequency multiplier on the setup in question. I may not be able to report on that any more because I am leaving my current company and won't be able to work with the PowerBrick any more.
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#11
For the PWM-Frequency, I had it set to 30kHz, I think. I unfortunately won't be able to investigate that matter any further as I am not going to work on that experiment any more. However, I instructed my successor about it.

It could be a consequence of the problem we had in tuning the current loop. And I did not retune the current loop after having changed the the pwm-frequency multiplicator. I think that is the explanation for this problem.
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