I'm preparing a configuration for my small drive unit, and I'm happy that I understand the parameters with two exceptions: fconst and fslipconstmax
Please could someone describe the difference between when fslipmax is used and when fslipconstmax is used?
In all the configurations I've seen, fconst is higher than fweak. The documentation suggests that in this case, fconst will not be used. But then what happens with fslipmax and fslipconstmax?
Thanks, and sorry for my incessant questions this week!
fconst and fslipconstmax [SOLVED]
- catphish
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Re: fconst and fslipconstmax
I've actually just read the source code and I think what's confusing me here is the documentation:
Am I right in thinking that in fact fconst has an effect when it's greater then fweak?fconst - Frequency where slip frequency is derated to form a constant power region. Only has an effect when < fweak
- catphish
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Re: fconst and fslipconstmax
The relevant code is https://github.com/jsphuebner/stm32-sin ... L105..L114
It seems like weird things would happen if fconst was actually < fweak. Anyway I think this makes sense to me now, but if I'm correct, then the documentation is confusing.
Code: Select all
if (fstat > fweak) {
float fconst = Param::GetFloat(Param::fconst);
float fslipconstmax = Param::GetFloat(Param::fslipconstmax);
//Basically, for every Hz above fweak we get a fraction of
//the difference between fslipconstmax and fslipmax
//of additional slip
fslipmax += (fstat - fweak) / (fconst - fweak) * (fslipconstmax - fslipmax);
fslipmax = MIN(fslipmax, fslipconstmax); //never exceed fslipconstmax!
}
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Re: fconst and fslipconstmax
See what you mean
Frequency where slip frequency saturates to form a constant power region. Only has an effect when > fweak
So should sayFrequency where slip frequency is derated to form a constant power region. Only has an effect when < fweak
Frequency where slip frequency saturates to form a constant power region. Only has an effect when > fweak
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- catphish
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Re: fconst and fslipconstmax
I've updated the wiki:
fconst - Maximum slip is increased from fslipmax to fslipconstmax as frequency approaches this value. Only effective when greater than fweak.
fslipconstmax - Slip frequency at maximum throttle and fconst. Set equal to fslipmax to disable.
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Re: fconst and fslipconstmax
On a strongly related note, what is the *purpose* of fslipconstmax? Is this purely to reduce torque at lower RPM?
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Re: fconst and fslipconstmax [SOLVED]
Thanks for that.
It increases slip past fweak to slow down torque drop off. Running that kind of slip below fweak would over current the inverter (and perhaps the motor)
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