High voltage & high power servo drive design

[Xerxes]

Since our upcoming servo drive VSD-E will be 12-80 VDC drive and there is a clear market for high voltage drive that can be operated directly from mains voltages (115/230VAC), I'm creating this poll to gather user opinions about preferred servo drive constructions.

I have 3 different drive types in mind that would allow such operation:

1. VSD-E without on-board power stage. It would just have connector for external power stage.
2. Small sized control card with pin headers. This could be plugged on "mother board" containing the power stage.
3. Monolithic design. Everything on one board and possibly a metal enclosure for it.

Options 1-2 allows controlling virtually any power and option 3 would be the easiest to use.

Attached picture shows VSD-E drive if one isn't already familiar with it. Option 1 would look much like, but 1/2 of this size.

[Billhill]

The board looks great, except it looks like it's missing a rather large heat-sink. Adding a heatsink looks difficult.

I LOVE the voltage range, it's perfect. Most serious servo motors want 80-90VDC for their rated performance specs. I'm so sick and tired of drives and amps which seem aimed at the combat robot/wheelchair style builder who is limited to 24VDC.

I note you call it power supply, though you may actually mean servo drive, which uses a high voltage/high current power supply to power a high-torque motor or gearmotor combination.

FYI, my motors are the odd duck ServoDisc motors, so my power supply is customized for them. My development is still underway, the first phase will be limited to about 31VDC, and later expanded to approx 80VDC.

Since I've purchased a lower voltage drive for 3 channels, I've been thinking about using it's output to modulate an external circuit running at 80VDC (MOSFET switching of ground). I worry about presenting enough of a load to the amp for it to remain happy.

Comments?

[H.O]

Hi,
I vote for a control card with separate powerstage. That way you can have 2-3 different powerstages available so the user can choose which one he/she wants when ordering. 80V/20A, 200V/10A, 200V/25A or something like that.

That way it's also possible for the end-user to design his own powerstage. However, that may end up as a huge support issue for you...

Next choice would be a VSD-E with a voltage rating of 200V. I guess that would be number (3).

/Henrik.

[Xerxes]

Billhill, the drive in picture is without heatsink because powerstageless pure control card wouldn't need any. You need to add inductor in series with disc servo to be able to use it with a normal servo drive.

Henrik, I'm planning to try some day equipping VSD-E with 200V MOSFETs. Drive rating could be around 160-180VDC max. However current rating would be only about half of 80VDC verson.

Personally I'm feeling that option 2 would be my choice. It has the best flexibility and could be used to build type 3 drives too. Attached picture shows sketch of option 2.

[H.O]

Henrik, I'm planning to try some day equipping VSD-E with 200V MOSFETs. Drive rating could be around 160-180VDC max. However current rating would be only about half of 80VDC verson.

But then it's about the same specs as a VSD-A, right?

[Xerxes]

It would be weaker than VSD-A, maybe 5-8A cont and 15A peak max. There aren't very good 200V MOSFETs available but I was thinking to try IRF640N. Because demand is for higher currents, I'm wondering if it's worth effort doing 160V version of VSD-E at all.

[H.O]

Well, I can only speak for myself but I'd like to see a 160V/25A VSD

Regarding the availabillity of 200V MOSFETs you probably know that better than me but I think you need to move to larger MOSFETS than what is available in TO220 package. As you might know the HP-UHU uses IRFP264N in TO247 package, rating is 250V, 44A.

The features and performance (true torque loop, feedforward, high res encoder etc etc) of the VSD coupled to a powerstage rated at 160-200V, 20-25A continous would be a sweet thing IMO.

Again, this is just my personal thoughts, you certainly have a better overall view of the market than I do but it's not uncommon that people ask for 200V/25A drives on the Mach3 list for example. With Rutex currently in a somewhat unknown state and the Pixies S/D->analog converter being discontinued you really don't have many options when it comes to driving larger servos.

/Henrik.

[Xerxes]

The problem is not finding a large enough MOSFET but finding a good enough. High voltage mosfets have nasty properties compared to <100V ones, so they need snubbers etc to work nicely. It needs much more design effort than just equipping existing PCB with alternative parts. Perhaps some day (not anytime soon) I start such project for high power VSD-E.

However, controller-only card allows doing that any time. It allows making drive that works straight from 110-230VAC which is a good advantage. So when (inexpensive) controller card is available, I hope to see third parties offering reasonably priced drives built around it.

[routerman]

I do but it's not uncommon that people ask for 200V/25A drives on the Mach3 list for example. With Rutex currently in a somewhat unknown state and the Pixies S/D->analog converter being discontinued you really don't have many options when it comes to driving larger servos.

Larkens Viper 200 drives will drive motors up to 170 volts and 20 amps. This is a DC servo drive, not an ac servo drive though.
http://www.larkencnc.com/viper/index.shtml


Here is a big mill retrofitted with them
HURCO mill retrofit

[H.O]

Hi,
Yes, I know about the Vipers. I looked at them too when shopping for drives but didn't go that route due to a couple of reasons.

Anyway, if they are running that big Hurco they might be 'ready'. If none of my current options works out (god forbid...) I might try them out.

[Xerxes]

I have nearly finished the "stamp" design (see post #4) and a reference schematics design for drive around it. It will take time to build prototypes and write firmware for it.

If product gets out, I would publish reference schematics of example drives. I have been thinking to design also a reference 400V/40A DC servo drive around it. It could end the lack of high power DC drives once and for all

[Xerxes]

Ingegration of stamp (VSD-Core) could look like this. Only few external components required.