Hello folks,
I'm new to this forum and before asking my question I'd like to say that this project is amazing.
I am planning to control a PMSM with 5 pole-pairs.
So if I want to have 20000RPM (for example) I'd need a sine-wave of (20000RPM*5pole-pairs) / 60seconds = 1.666 kHz right?
I was wondering, where I can find information of the maximum possible sine-wave frequency (or the therefore needed pwm-frequence of the fets).
Does anybody have a link / hint for me ?
Thank you!
Push :(
You are mixing up several terms which should not be mixed.
I think you are looking for the max ERPM (the electrical RPM) limit of the VESC. With the recent VESC I have seen/read numbers up to 150k ERPM you can maybe go faster I dont know the exact number.
The more realistic limit you normally run into is the KV value with respect to the supply voltage, that will most likely limit the systems RPM.
Hey, thanks for replying.
I am thinking about this:
The Vesc will produce a sinewave for my motor.
In order to do this, it switches the Mosfets / IGBTs on and off at the calculated times. (Calculated by FOC)
The higher my ERPM (= RPM * poles) the higher the switching frequency of the FET/IGBT to generate the needed sine-wave signals.
(which are needed to generate the rotary field)
To generate a sine-wave from dc-voltage it is needed to approach the sinus-shaped curve by pulsing the dc-voltage.
The smaller the steps, the more accurate/precise the sinus-signal, but the higher my switching frequency.
And that is why I am looking for the switching frequency of the fets, which summarizing seem to depend on:
Depending on the maximum switching frequency I need to choose my Mosfet/IGBT. (Among other sizes such as maximum current etc.)
So in one question I should have asked:
How do I find out/ where do I find the maximum of switching frequency of each single Mosfet/IGBT.
Hopefully I did not express my self too confusing and someone can help me.
I found something. The switching frequency can be set in the Vesc-Tool. It can be found at the advanced-tab in the FOC-chart.
The description says "The controllers and estimators will run at half of this frequency"
Yeah, you're still a little confused.
Don't worry about sinewaves. The ESC will generate the correct signals provided the motor RPM multiplied by the number of poles is less than the maximum number 150,000 ERPM.
If your motor has 5 pole pairs (that's kinda low, scorpion motor?) then you have a max RPM of 150,000/5 = 30,000 RPM
The default MOSFET switching frequency is 40kHz, unless you're fully aware of what you're doing I wouldn't touch this as it's easy to burn your ESC by putting in the wrong values.