Follower with encoder or no ?
Follower with encoder or no ?
(OP)
Hello everybody,
I have a one question for you. If I use two AC induction motors mechanically coupled with 2 ABB drives ACS800 (direct torque control) and if they are working in master follower configuration is it better to put encoder on follower or there is no sense to do this.
Thanks.
I have a one question for you. If I use two AC induction motors mechanically coupled with 2 ABB drives ACS800 (direct torque control) and if they are working in master follower configuration is it better to put encoder on follower or there is no sense to do this.
Thanks.





RE: Follower with encoder or no ?
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Follower with encoder or no ?
OK but I meant that follower should be torque controlled (sorry because I was not precise) and in this case do I need encoder. So the main question is if drive that is torque controlled slave use speed information from encoder in torque algorithm. Concretly I mean on ABB ACS800 drives.
I make this question because as I learn DTC dont use speed information in torque algorithm and when I look behavior of ACS800 drive it seems to use it.
Thanks.
RE: Follower with encoder or no ?
In some firmware manual it is written exatcly this:
"Pulse encoders are recommended to be used in all of the torque controlled Followers"
RE: Follower with encoder or no ?
If you need better than 10% of motor nameplate slip speed error, you should use an encoder on the lead drive (speed regulator) only.
RE: Follower with encoder or no ?
If you need better than 10% of motor nameplate slip speed error, you should use an encoder on the lead drive (speed regulator) only.
RE: Follower with encoder or no ?
RE: Follower with encoder or no ?
But,
I just wondering if torque algorithm use speed information than MAYBE if you are on some small speed with high torque required, follower will not do his job correctly ( real torque on shaft will not be as drive think) and then master will need more torque or you will have some oscillations.
So this is my theory why ABB recomend that follower should have encoder. Probably I am wrong, but never know.
I dont believe that they recomend encoder on follower only because some speed limits or in case shaft breaking. For me estimated speed is good enough to do this.
RE: Follower with encoder or no ?
Some of you probably see this situation.
If channels A and B on encoder card on ACS800 are mixed (positive torque generate speed that drive see as negative) and drive is in speed control and you give start command with some positive speed reference shaft will oscilate around zero speed.
This behavior is what is very strange to me.
To me it is logigal that in this situation drive generate positiv torque and motor should start rotating in positive direction and because channels are mixed drive will see that speed is negativ. Then drive should generate more and more positiv torque and speed will be more and more negative (in drive) and at the end you will have some encoder fault.
But drive not react like this. Motor oscilate around zero speed.
So to me this behavior tells me that drive use speed information in torque algorithm.
Correct me if I am wrong.
RE: Follower with encoder or no ?