Load sharing between two drives

I have two motor that are rigid coupled and drive a belt.
What is the best way to share the load between both.
A need a controlable speed for the belt.
The drives are Unidrive SP.
I know there are different principles to share the load.
Tell me your experiences with loadsharing (whatever brand it concerns).
Thanks.

The simplest method, that is often the easiest to incorporate, provided the drives can handle it:
1) Make the master drive a speed regulator, the slave drive a torque regulator.
2) Take the Torque Command output from the master drive, and feed it to the slave drive.

This assumes, of course, that you can get to the post-speed regulator torque command, and even more, that the drives can operate in a real torque mode. Many lower end AC drives cannot.

I'm with rdrast if you don't have a separate free-standing controller that can put out a torque command. I have used the velocity master/torque slave method on dual spindle unwinds and rewinds quite effectively.

But again, if you have a high bandwidth controller that can directly put out a torque command, run both drives in torque mode and run the torque command in parallel to both drives. I have seen multi-motor cut-off knives done this way.

Keith

I don't know what your speed accuracy requirements are but, if they are 1% or more error, a very simple arrangement is to power both motors in parallel from one drive.

The motors must be identical. Otherwise, rdrast's system is the best, in my view, as long as there is no reasonable chance that the follower motor can break away and run up to max speed on its own.

Or you can use droop control, i.e. the drive with the heaviest load decreases the speed to let the other drive share the load.

Here are the setup parameters for a MM440, check P1488-1492.

Kalle

Read or get your hands on the Control Techniques drives and controls handbook

Here it the link to the load sharing section on google books

If you are open loop, look at parameter 5.08 which is droop setup


http://books.google.com.au/books?id=KPpl49vhgDAC&pg=PA271&lpg=PA271&dq=control+techniques+drives+load+sharing&source=bl&ots=EO5DEfSrj2&sig=K_yZ_E7EAXBjvDIszhv5y0PgTI4&hl=en&ei=mXG_TMLyHou2vQPo7I01&sa=X&oi=book_result&ct=result&resnum=5&ved=0CDAQ6AEwBA#v=onepage&q=control%20techniques%20drives%20load%20sharing&f=false