DC closed loop Motor running with no speed reference.

[KcGav]

Hello, Newbie on here but thought id give it a go..

I have a paper converting machine which is built up of sections, each is driven by an ABB 220A DC motor controlled via ABB DCS drive. Eachs ection of the mechine is sent a speed refernce via a fibre optic link, the speed reference is a master ref corrected dependent upon a dancer bar position. each motor drives steel/rubber rollers wieghing approx 2-3 tonne.

Under normal conditions all 4 DC motors ramp up and ramp down together very closely (so close a single ply of tissue can be passed through each section with out snappping)

My problem is that one of these sections motors, when ramping down is running on for longer than any other section even though the speed ref sent from the PLC appears to be a zero. in summary every section ramps down to a stop but one section runs on for approx 3-5 seconds.

I have attached two graphs, they are trends of the offending motor, one graph shows a good ramp down to 0m/min the other shows the fault when the motor runs on.
You'll notice that when the motor runs on the current rises more steeply as if the drive is over compensating.

My proposed theory....
If there was a mechanical failure casuing extra load on the motor, it would cause the motor to ramp down faster, as if being braked. The drive can see the motor is slowing to quickly and tries to compensae for this by applying some positive current/torque. but this current causes the motor to slow the ramp down too much and thus the motor takes longer to stop?

Red= motor speed
green= motor current
cyan = torque
blue = speed offset from ref

Any ideas anyone?? Fire away with the questions...

 

[KcGav]

2nd graph

 

[Skogsgurra]

It would be a lot easier to interpret your recordings if you hadn't played with the offsets. Also, a p.u. or percent representation would make it much easier to follow what is happening. It may be OK for you, but it is really hard for us that want to help but are not prepared to get a minor headache from finding out how to read the traces.

Could you, please, show again the offending drive with no offsets and a percent or p.u. scaling. A speed reference trace would be of great help.

Also, not everyone can figure out what ERR:OUT is. Is it speed controller output - or something else. Or is it SPC:OUT that is SPeedController output. If so, what is ERR:OUT?



Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[DaveAlford]

I only see one graph (GRAPH06.bmp)...did the second one not get posted?

 

[KcGav]

The ABB engineer set up the graphs and the scaling, i am awiting the software to allow me to take the reaidngs myself. The ERR:OUT is the diference between the actual motor speed and the reference, you can see in graph06 that the ERR:OUT shows that the speed reference is at zero but the actual is not. I have a seperate graph i will post which was trended from the PLC, this shows the speed reference and actual speed of the offending motor and a different sections motor acting correctly. GF1 is the correct response, GF2 is the wrong response. you can see the pink line continue as the blue line stops to zero.

Dave can you now see all three graphs?