In our plant, we have a delta supply and do have periodic grounding issues from machines having shorted heaters on them so, now comes the next step. We now have some machines that have been converted over to AC micro drives. (VS1MD). It seems that these little machines will operate find in the shop/R&D area most of the time 100% as expect how ever, we been finding that in some areas of the plant they are not operating correctly..
They are giving random side effects. Things like the PID seeming to loose control at random (Web Control) or the drive just seem like it wants to not respond like it should while the feed back is getting dangerously close to limit position and then it'll come to life and over shoot! AFter that, the drive may over exceed correction and hit the other limit. If it does not, it most likely will correct itself and be happy with a normal acting control, again.
It would almost be like excessive load and the drive has insufficient HP to control it how ever, it works fine in the shop. Today, It hit me. In the problem area these units are being used, we do have a known problem with the buss and happens to be a Delta that some where has a random grounded leg.. We had to install isolation transformers in the water system which is near by, which use Parker Drives (Eurotherms), because they were spitting out Buss Over voltage errors, one actually blow it's gutts out of the bottom! Don't know if that had anything to do with it how ever.
I know most of you probably don't have experience with the Baldor Micro Drives (VS1DM), but do you think this type of buss problem could cause what appears to be firmware problems to actually be ground loops screwing around with the control logic in the drive?
I just find it hard to believe with how many of these things out there that poor software would exist at this level. On a second note, I did find a reproducible error though! if you open the stop circuit, have the dynamic brake come on, and vary the input reference to min/max and back real quick, it puts itself back in run mode! regardless the state of the RUN command at the terminals. I mean, even if you cycle the Run terminal, it stays in RUN mode and operates in RUN mode.. This means the operator can not switch off the drive, they have to kill power to the drive!... what a dangerous thing!
Oh well...