I got an article on this link. In this article the author chooses a PWM frequency of 31,372 Hz to get a smooth signal.
How do these frequency values get a smooth signal?
I've read other articles on the website but I can't find the answer.
Electronic – How to choose PWM frequency
frequencypwm
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Best Answer
The cutoff frequency of the lowpass filter you are using determines how low a frequency you can use and still have it be smooth. But your cutoff frequency places an upper limit on how quickly the output signal can respond. So if your cutoff frequency was 1kHz, you aren't going to be able to produce a 100kHz signal. You will probably only get to choose your filter if this is a DAC. If this is a power application like a motor, then the filter has already been chosen for you (the motor inductance).
If this is not just a DAC and you are actually driving a lot of current with the PWM, then you can't use too high a frequency either because this increases switching losses and will overheat your switches.