VFD causing noise on deceleration 1

[Jachord]

I have a piece of rotating machinery that is experiencing vibration and noise in the 200 to 300 RPM range on powered deceleration. The noise and vibration is gone when coasting to a stop. No noise or vibration on acceleration. This speed range is also a natural resonance point for this machine but the vibration is considerably higher with the powered deceleration. I have seen many reports of torsional torque harmonics at specific speeds but nothing during deceleration.

Has anyone ever seen this or have any suggestions? Without the noise happening while free wheeling we do not believe it is a mechanical issue.

 

[itsmoked]

So; you're saying that if you coast it to a stop - no vibration.
And a controlled stop - vibration.

Does it stop in a shorter time coasting?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Jachord]

No takes at least 15 minutes to coast and only 5 on powered deceleration.

 

[itsmoked]

Interesting problem you have there.. Normally a VFD that's bringing down a load has a bunch of energy appear on its internal capacitor storage due to the reclaimed kinetic energy. The voltage will continue to rise until voltage specs are exceeded and something fails. To prevent this a braking resistor is included somewhere and a separate circuit exists to monitor the voltage on the capacitor bank. When it reaches a certain level it connects the capacitor bank to the braking resistor to 'burn-off' some of the stored energy to maintain a limit on the voltage. This causes intermittent step voltages on the capacitor bank that could be relating to your deccel torque pulsations. Not sure what I'd do about it... I'd normally not expect the capacitor bank voltage to even make much difference in a load deccel.

Time for more details.

What voltage is this?
What kind of machine is this?
What make and model VFD are we talking about?
Did this problem 'just appear' or has it always had this problem?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[edison123]

In the critical speed zone, even a small excitation force, be it mechanical or electrical, can increase the vibration of the rotor (not sure about the noise). May be during forced deceleration, your VFD is introducing some electrical harmonics that are worsening the vibration in the critical speed zone.

Muthu

http://www.edison.co.in

 

[Jachord]

OK so it is on a centrifuge with a rotating assembly weighing 1000# running at 1100RPM, 750RPM,and 60RPM during different phases of the process. It is a Yaskawa drive not sure of the model but it is a regen drive for 20hp motor. It is a new installation. Voltage is 460. Motor is Baldor 20hp 256t explosion proof.

It is a regen drive so no brake resistor unless it is built into the drive. The drive should be dumping the excess voltage back into the source.

If the machine was only run at 1100 RPM it would be fine but it has to drop to 60 RPM every 20 min.

Planned actions are to change the speed control from voltage to vector, tune the drive, and possibly program the skip frequency. The unusual thing is that it happens on decal so not sure if any of this will fix it. Everything points to torsional torque harmonics but all of the cases I have read about indicates that this occurs during acceleration or during normal running speed.

Thanks for the help so far.

 

[Strong]

You may have a torsional resonance that causes drivetrain (coupling or gears) to chatter when decelerating. This would be a mechanical issue with electrical excitation from VFD. During acceleration there is a bias torque on the drive, while during deceleration there very little allowing drivetrain to bounce/chatter.

Walt

 

[waross]

Centrifuge? 15 Minutes to stop coasting? The motor will be into strong regeneration as it de-celerates.
Try changing the deceleration ramp.
If the motor will accelerate without vibration in the forbidden band there is a strong possibility that it will decelerate smoothly using the same ramp.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[BrianE22]

If nothing else helps try increasing the de-acceleration rate (stop it faster), if possible. It will be in the resonance zone for a shorter period of time and the amplitude of the vibration may be less.

 

[Skogsgurra]

We are just now looking at a similar thing. But this is a human centrifuge for fighter pilots training. A boom with resonance at a few Hz starts shaking the pilots to pieces during deceleration. We first thought that there was a transmission with raw cog flanks in brake mode direction. But it turned out to be a problem with gate drive in the regen unit.

That could be your problem, also. But I think it is more plausible that your (still quite new) transmission either wasn't made for four quadrant operation or simply has to be ran in. Most transmissions are designed for torque in one direction only. Your cycle is somewhat unusual with its long braking period, which means reverse torque.

A simple test would be, if at all possible, to accelerate in reverse direction and see if you get the vibration during acceleration.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[jraef]

If it is the Yaskawa U1000 or Z1000U “Matrix Inverter”, it’s possibly an issue with the commutation of the bi-directional transistors that are unique to that design. I’ve heard from a user that they don’t like long slow deceleration profiles, especially if there is a mechanical resonance, i.e. an unbalanced load. The example given to me was a gold concentrator, a large conical centrifuge. It had no problems with an empty bowl at the end of a batch, but if they went to stop it with material still in it, the matrix drive would interact with the mechanical resonances and become unstable. I didn’t witness this myself, this was described to me during discussions about using more conventional line regenerative AFE drives.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[Jachord]

Thanks everyone I will forward the information to the Yaskawa rep when he arrives on site today. As this is a direct drive splined motor it almost has to be a reaction between the motor and VFD. I appreciate all of the input.

 

[lectricwes]

Check your ASR settings. Sounds like your motor may be "hunting" during the decel.

 

[Strong]

Perhaps the OP can describe the solution to the noise problem; if solved.

Walt