DIY Variable Frequency Drive

It’s still motor drive but rather different. I am looking for a VFD that can do 3000 hz and they are pretty uncommon. All they really do I think is output a sine wave, they ramp the frequency and voltage though. The b-g431b-esc1 board could update the motor.move() at 37.5 khz. If I could up that I might be able to just use one of these boards as a vfd for my low power spindle, it’s a PCB milling spindle that does up to 50,000 rpm. With these kinds of motors, the frequency is approximately proportional to RPM (there is some “slip”, unlike a synchronous DC motor, when the difference between the rpm and frequency grows the torque grows).

Bad idea? The spindle is only rated at 500 watts and I doubt I will use 200 most of the time. Gotta cut back somewhere, and it’s an intriguing new region to explore. There are a lot of spindles like this kicking around on ebay for $500 each.

oh wait I think the voltage is like 220 volts. Any idea for a power stage that can handle that that I could grab and use with a nucleo board?

I think you would need loop frequency many orders of magnitude higher than the rotational frequency for that to work, I think.
Are VFD usually driven with FOC? I don’t know much…

Not many orders of magnitude. That would mean hundreds or thousands of times. Ten times seems a little low though. It’s not a noise sensitive application so it might work.

No, vfd and foc is totally different, I just want the sine wave generation and voltage and frequency control stuff. Maybe I can gut the code to get it to run faster, it seems to be pretty good the way it is though. Maybe there is a nucleo board with double the clock rate or something. These VFD things are pretty expensive, like $500 for a cheap one. They are usually capable of much greater power than I need though, and they include the power supply but one capable of 220 volts will need a transformer anyway so I have to pay for that. Total drive solution is in the $650 range with aliexpress stuff.

For a FOC VFD would it be enough to sense zero-crossing and then blindly fire a sinewave with the right frequency? That way the FOC loop would only need to be twice as fast as the spindle.
To control slip angle, you’d compare the real frequency with the FOC frequency.

For 50k RPM I’d look for pneumatic drives. Like your dentist has. They are also pretty common in PCB-drilling.
In the end, you don’t need real RPM control. You want to spin as fast as possible, right?

They don’t use pneumatic drives in pcb milling, those are gas bearing spindles. They still have electric motors. You don’t have to sense zero crossing, there is no zero crossing involved, here, it’s not a dc motor.