ac against dc

[lesliemcg]

hoping for some sound advice, existing motors on a machine are all d.c. permanent magnet 2 hp controlled by regen drives (4 quad), taco feedback. the system requires the motors to change speeds via pid control. the motors dont hold weight i.e. a lift system. i am building a copy type machine but considering using ac, what type of ac controller should i use to give the same performance. should the ac motor again be 2 hp like the dc version
any help will be light at the end of the tunnel

 

[jraef]

#1 problem with regards to your application as described, no regen on AC drives at that low of HP, at least not cost effectively. You could go with the type like Control Techniques' Unidrive that can be configured to have 2 drives back-to-back, one as a drive, the other doing the regen, but this is going to cost WAY more than you probably want to spend. You are probably better sticking with PMDC if regen is important to you.

If regen is for braking, describe the braking application and maybe there is a less expensive way to go.

Quando Omni Flunkus Moritati

 

[lesliemcg]

the braking application only slows and speeds up the machine, it is a wire feed unit to give a constant 'flow' of wire (0.5-2mm) spring gauge back from a pid controller (plc)
thanks again
lesliemcg

 

[QUIPPDUDE]

Many models of AC drives are equipped available with an internal PID function. You do not state the range of RPM and accuracy of speed regulation you require.
AC Vector drives offer excellent speed regulation at lower RPM. How much can you afford? Servos will attain the highest speed regulation and torque at all speeds!

The knowledge center at

http://www.drivesmag.com

is an excellent resource for drive and motor issues.

 

[RadarRay]

AC vector drives should work adequetely as a substitue for your DC system. The same size HP's should also be fine if you are using vector drives with motors for Constant Torque application. The only real question is weather you need Regen or not. From your description I would have thought DB breaking on the drives would be fine. You don't mention how many drives, but the AC drives could be common bussed where only rapid stopping would require the use of the DB's. For a better analysis, I would like to know how many rolls are driven and what function they actually perform.

My preference would be Eurotherm 690+ drives.