VFD for linear motors

[M0rt]

Hi, All,
Does anyone have any experience of using a standard VFD to drive a linear motor? Or are you aware of any VFD's which will work with linear motors without a world of pain? Motor in question is 415V, 50Hz, 5m/s, 3A.
Thanks for the help in advance,
Mort

 

[ScottyUK]

I'm fairly sure that Control Techniques' Unidrive is capable of running a linear motor, perhaps in a servo-type application. I was looking at the drive for a much less demanding application a week or two ago and I noticed linear motors in passing. Their technical people used to be knowledgable and helpful a few years ago (which is the last time I spoke to them, and that was about a DC drive) but that is pre-Emersonisation and things may have changed since then. Hopefully not - it only takes a phone call to find out!

 

[roydm]

I ride back and forth on the Vancouver skytrain, that uses a VFD with a linear motor but I can never find any details.

 

[itsmoked]

I don't know which VFDs do that but after doing a very tough motion application I would never attempt another without a trusty AKD servo drive from Kollmorgen. The built-in analyses aids and excellent software tools allow absolute control of every single aspect of the motion. That's position, acceleration, and jerk. You can control the current profiles too. The drives have built in logic like a PLC to handle hand-offs, synchronicity, and gearing. They handle linear motor applications where the shuttle moves too fast for the eye to follow. You can take snap-shots of everything involved in the motions and see it all on a laptop to Ethernet into the AKD drives.

The rep I used was also amazingly competent, educating me, and knowing his products at a level rarely seen.

[URL unfurl="true"]http://www.kollmorgen.com/en-us/products/drives/servo/akd/[/url]

Contact me if you're interested in this and I'll introduce you.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[jraef]

Rockwell PowerFlex 755 drives can be used on Linear PM and Linear Induction motors both. Rockwell bought Anorad a while ago and integrated their linear motors into the fold, then adapted the PF755 to be able to run the larger ones (where they were too large for the servo drives). Lots of them are in use on linear induction motors for amusement park rides all over the world.

Disclaimer, they sign my paycheck... but that's the only COTS VFD I'm aware of that does this simply because linear motors didn't really hit the market until after I came here, and I haven't had to investigate anything else now.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[GroovyGuy]

The original ASDs, driving the Vancouver Skytrain linear motors (cira 1985) were made by GEC (ie General Electric Company of England, not GE (USA)). I'm sure that these original drives have been replaced by now.

 

[M0rt]

Thanks, everyone, for the quick and interesting replies. There is certainly plenty of information for me to investigate further.
@Jraef - Am I correct in thinking that the Rockwell VFD is what I would call a "standard" drive, it presumably has encoder input for the speed feedback?
From my initial searching, it seems that servo drives are normally used for Linear motors, and the common control scheme is to use a fixed output frequency and vary the voltage to control the torque.
I've also seen hints that there can be large differences between manufacturer's motors, and there are also differences depending on the speed the motor is designed to run at (i.e. the synchronous speed).
Once again, thanks to all. If you have any other information, please post, I will relay any information I find interesting or potentialy useful.
Cheers,
Mort

 

[jraef]

There is now an "open loop" Flux Vector Field Oriented Control output option for the PF755 drives that provides nearly equal performance to the closed loop.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[waross]

As I remember the first line used two 400 HP LIMs per car. The cars were supplied with DC by brushes running on two bus bars adjacent to the rails.
I did not work directly on the cars or drives. I did the trouble shooting, testing and commissioning on the Integrated Alarm Notification System (IANS) at Stadium Station. At some of the stations you will see large resistor banks used to burn off energy when the regenerated energy exceeds the consumed energy. In other words to limit over voltages on the DC bus.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[roydm]

We have 3 generations of cars now, the system has been expanded since you were here.
I think there may be some form of pole changing to go with the VFD, to tell the truth we just take it for granted these days.