Control Issues for Direcet Coupling of Motor Systems 1

[Dyno22]

What is the best control methodology when direct coupling motors together that has separate analog controllers? I have two 300HP DC motors that I would like to couple together for the additional horsepower capability. I assume I would have a ‘master-slave’ arrangement where the feedback torque or current from the master that is in speed mode, would be the set point to the slave machine that is in torque or current mode. I have a configurable PC/front end controller that will be controlling both dynamometer systems. Does this make sense and are there problems I should be aware of?

 

[TomG33]

hi newb
you are correct in that when you have two motors directly coupled together, you need a master slave configuration.

most Drives Operate with an internal current regulator to control torque, Receiving the torque control command from an external voltage or speed regulator.

If I was doing this, in a motoring configuration, I would have the Speed regulation done in the master, with the output of the speed regulator ( torque Command) fed to the current regulator of both the drives.

as Long as your scaling is correctly done on a "Per Unit" Basis, The load sharing should work pretty well, Even if the motors are of different Horsepowers.

What you have to watch out for, thou, is the possibility that the coupling on the slave motor could break, or become disengaged.

If this happens the second motor would still be producing the same torque, but with no load against it, resulting in the motor accelerating without control. Even thou the consequences of this are not as dire as they were back in the old "MG Set Days" it is still worth thinking about what you could put in place to guard against this.

If you wanted to operate as a torque regulator, you would simply issue the torque command from your controller to the current regulator of both the drives.

It would still be advisable to have the speed regulator active in this situation, But not in control, just in case you again suffer a broken coupling somewhere. Excessive error from the speed regulator produced by the run away motor, could be used to shut off the torque command to prevent injury or damage.

Tom

 

[jbartos]

Suggestion: Visit

http://ieeexplore.ieee.org/xpl/abs_free.jsp?arNumber=16756

for directly coupled dc motor adaptive concept. However, direct coupling induces a large sensitivity to load variations, so the desired response and the reference model in the adaptive controller are adjusted to the motor capabilities.
However, the concept for the two motors sharing a load would have to be added/developed.