Build Log: Servo Drive and VFD with vector control

[EddyCurrent]

Re. stepper motor use.
If you are splitting the power section onto a separate board maybe you could use a common DC link psu to power several controllers. I suppose this is what the current stepper drivers do.
Also if you fit encoders maybe it would be worth including a system for homing a master /slave without external intervention.
Keep up the excellent work

[Jonathan]

Re. stepper motor use.
If you are splitting the power section onto a separate board maybe you could use a common DC link psu to power several controllers. I suppose this is what the current stepper drivers do.

Currently the design has a rectifier so it accept an AC input, but I also put connection to the DC-link so you can power from a DC source, add more capacitance or share between drives. One interesting consequence of connecting the DC links in parallel is energy can transfer from one motor (regenerating) to another, which is a regular occurrence on a CNC machine as often when one axis is decelerating another will be accelerating.

If instead of adding an extra leg I connect the stepper motor to the 3-leg inverter, as mentioned in my previous post, the only obvious disadvantage is you end up with 'poor' utilization of the DC-bus voltage, V. Depending on the output voltage vector angle, you either get V or V/sqrt(2). See this paper, fig 4. I don't think that's an issue though, as we can simply supply the motor from a higher voltage to compensate. The current controller bandwidth will have to be a little higher to compensate and the insulation resistance of the motor also must be greater, but I don't think the difference in voltage is a big enough factor to matter in either case. Maybe there's something I've missed, as it seems strange that all commercial drives seem to use 8 mosfets when this method only needs 6.

Also if you fit encoders maybe it would be worth including a system for homing a master /slave without external intervention.

Yes, why not ... it's just software. When I've got the code tidy enough I'll release it as open source and hardware, then people can add things like that if they like. Also the encoder I'm currently using is absolute, so homing is trivial.

I've started soldering five of the PCBs. It's very time consuming though, maybe I should make a pick and place machine next.

[Erythros]

I think that separate controller board and inverter with power supply is the only way to go. I recetly began looking into PMSM control and the differences in motors are too big to use one MCU/power stage combo. On eBay there is plentiful of used servomotors from industrial machines (probably from modernization/retrofit), which are quite cheap and for us hobbyist still good enought. And the difference in DC link bus voltage of inverter stage is huge. The motor I bought has the original driver using 670V DC link, some Fanuc ones use about 100V and so on. Also there is difference for power resistor for dynamic braking and other aspect of design that make me think that ability to differentiate the inverter is only way to go for general purpose driver.

[Jonathan]

I think that separate controller board and inverter with power supply is the only way to go. I recetly began looking into PMSM control and the differences in motors are too big to use one MCU/power stage combo. On eBay there is plentiful of used servomotors from industrial machines (probably from modernization/retrofit), which are quite cheap and for us hobbyist still good enough.

I tend to agree. Since we're not too concerned about efficiency you can get some way by over-rating the components, which doesn't increase the cost too much, but you soon become limited by the switching frequency (and thus control bandwidth) that can be used.

On eBay there is plentiful of used servomotors from industrial machines (probably from modernization/retrofit), which are quite cheap and for us hobbyist still good enough.

I've been vaguely looking out for one to try, as my driver may not be working well with position control just due to the non idealistic properties of the motor I've been testing with.

Really trying to keep the ball rolling with this project, but my PhD work and related things keep getting in the way as I tend to be spending 9am~8pm in the lab. Still, I have however done some more soldering on a few of the PCBs. Here are a few pictures:



Can anyone spot the mistake in this one...



Time to stop now though as it's 1:30am and I don't want to miss the eclipse this morning...

[Gotty101]

I cant see that great on my phone, but is it that component across the pins on the microcontroller?

Great work!

[Jonathan]

I cant see that great on my phone, but is it that component across the pins on the microcontroller?

Yes that's right - I accidentally connected the core voltage regulation filter pin to Vss instead of the capacitor. Fortunately that pin is only connected to a capacitor, so I'm instead lifting that pin and soldering an 0402 capacitor between it and the adjacent Vss pin. Bit fiddly, but it works ...

I've not found any other mistakes yet.

[JAZZCNC]

I've been vaguely looking out for one to try, as my driver may not be working well with position control just due to the non idealistic properties of the motor I've been testing with.

What Voltage motor would you want I have a few Large-ish Parker AC Servo motors.?

[Jonathan]

What Voltage motor would you want I have a few Large-ish Parker AC Servo motors.?

Sounds good. Anything up to around 300V, 15A would be fine. Do you have the part number so I can check?

[JAZZCNC]

Sounds good. Anything up to around 300V, 15A would be fine. Do you have the part number so I can check?

Ok will Dig out and let you know but i think it's much higher than 300v but I may have smaller one kicking around.