Inverter drive oscilates holding a load

Yep sounds like legal action in the making. You can do without customers like that!

This should be a simple inertia calculation and is probably obvious when watching this thing move in person in real time.

Your motors don't have enough *** to deal with the inertia of the load at the required velocity. This is evidenced by the fact that the voltage rises out of control. Even if you have enough ohms in your dynamic brake, you will likey run into the current limit next. The drive can't control both with that mechanical design, unless you allow the motor to become a 2nd braking heater and hope it welds a bearing when the winding burn in two.

For testing: I would add s-curve to the down cycle accel and make it long, and RTFM for any parameters the drive might offer to mitigate high dc bus voltage by extending the accel time. You will also need to reduce the top speed until you can see the DC bus voltage on the display never rises close to the trip level.

It will run slow if at all, but if the DC bus volts can't be controlled, it will drop until the mechanical brake kicks in. This can be dangerous and can be mitigated to some degree by dropping out the brake when the drive reaches a warning level but before it faults.

DO use encoder vector mode and advanced parameters for this application.

No matter what, ensure that the mechanical fail safe brake on the reel is up to snuff and have the hoist inspected by a 3rd party. Do not allow anyone to get underneath it ever no matter what until that is done, and keep your padlock hanging on the disconnect even just to go peee.

EDIT: I just went back and saw DickDV post where he says the motor IS big enough, and he did the math, I was just ranting on "gut" above.

Pierre,
You have not mentioned the presence of a drag brake in the hoist.
Does one exist? This is going back a few years for me to a discussion with a motor drive vendor who also sold and serviced hoists, but he told me that all hoists had a mechanical drag brake that the motor overpowered to move the load. This kept the load under control and lessened the load on any sort of spring set brake used to stop the load. He also had a rule that I remember to this day, "Don't stand under a hoist. Anybody's hoist".

Thanks Dick for the good advices.

Last news was the End-users want a ball park figure to make that thing good.

You all have to understand that we are dealing here with a WOW factor. When you look at this thing going you just say WOW!

Of course that was not really the case when it was doing its tarzan swing above other equipments. But still I feel its an amazing system. I am not considered a guy who is easaly impressed by systems. But this one I tell you is a real wow,

I have no clues on how it will end.

And it did have a mechanical brake.

Its a prototype. The schedule was to tight. The mechanical engeneering was less than expected. An incident happened.