AC Drive vs DC Drive

[bottler]

I have alot of VSD's (Inverter's)controlling all my AC motors,I would like to keep all the same and have found that I may need to use a DC Motor in one application, Is it possible to use a VSD on a DC motor? or is a DC servo pack the equivalent of an AC motors VSD?
any info is greatly appreciated.

 

[JatTiw]

Hi,
Before replacing DC motor with AC motor (ASD (Invertors) controlled) you should confirm how much is breaking torque requirement for that particular application. ASD driven motors still have limitation of breaking torque requirements.

 

[jOmega]

Brush Type DC Motor ?

 

[alfreds]

It looks like no-one has really answered your question! I believe the answer is No, you can't use a VSD on a DC Motor. A VSD produces AC voltage and current of varying frequency (and voltage), A DC motor can't use this. If you have to go for a DC motor you will need a DC drive.

 

[dydt]

hi..

would you mind explaining in details why you have to use a DC motor in ONE application as you mentioned?

dydt

 

[GusD]

Hi bottler

You could try a Brushless DC drive.They have Torque and Speed control equivalent or superior to a Flux Vector Drive.Contrary to Alfreds belief, that you cannot operate a DC motor from a VFD,this is in fact what the Brushless DC drive is Powered with.The VFD inverter only converts a DC bus voltage to AC power and therefore drive an AC induction motor.Some VFDs vendors actually claim that their VFDs can Power a Brushless DC motor or an AC Induction motor with minor changes.

If you like more info on the DC Brushless drives check Powertec wesite.

GusD

 

[RadarRay]

I find it hard to believe you cannot use a Vector AC drive to do whatever you want to do here. Just as dy/dt said, what is the application??

 

[bottler]

Thanks guys for the fast response.
I have a rotary valve ,with an ac drive and turn down ratio of 8.5:1,I cant get the control I want between the vsd , rotary valve , turn down ration to control the feed of product I need , I can either reach the high end of my outfeed rangeaccurately and not the low end or vise versa..

The guys that are building the unit have asked to use a dc drive and have spent alot of time investigating it and came up with this, that is why I ask.

thanks for all your help.

 

[Skogsgurra]

bottler

"The guys that are building the unit have asked to use a dc drive and have spent alot of time investigating it and came up with this, that is why I ask."

I cannot believe what you are saying. It sounds like a fairly simple application. I have measured 0 - 1500 RPM in 27 ms on a sensorless vector drive with 1 HP standard synchronous induction motor. The drive used was an NFO Sinus, but I think that you can have the same with ABB or Siemens little drives. And this is a lot better than what you could have with old thyristor controlled DC motors.

Is your application very special in any resepect? Or are you just dealing with the wrong guys?

One little thing: you can not run a DC motor from a standard frequency inverter. I saw someone saying the opposite - but that was on a philosophical note - not practical.

 

[jraef]

bottler,
In carefully reading your initial question, I think you may be asking a different question than what is being answered!

I get the sense that you want to "keep all the same" as in use the same VFD that you currently have, but use it on a DC motor. If that is the case, then the answer is most likely NO.

If you want to know if there ARE any VFDs that are configurable to operate DC motors, the answer is YES. The Unidrive from Control Techniques is one that I have seen, and there are several others.

If you want to know if SOMEBODY makes a VFD that will work in your application then the answer is YES, as pointed out by several others. Many manufacturers make a type of VFD called a Vector Drive which can make an AC motor duplicate the control features and capabilities of a DC drive and motor. Your application is not a particular challenge for that technology, which is what some of the other posters were pointing out.

If you want to know if your application can be done with an AC motor and YOUR favorite VFD, then perhapse the valve manufacturer has a point. Not all VFDs are going to be capable of doing the job. The valve mfgr may have investigated and found that YOURS will not work, and rather than try to sell you another brand of AC drive, they chose to stick with something that they know will work because they use it now, i.e. the DC drive and motor.

Please fill in the details as to which way you were going with this. We can then focus on the right issue.





Quando Omni Flunkus Moritati

 

[GusD]

Hello bottler

To Skogsgurra
I didn't mean to say Standard VFDs without mods.I mean't to say some Inverters are capable of running DC brushless with minor changes.
The info below explains it a little better.
Not all inverter makers have an inverter that will run brushless. Since a "brushless" motor is essentially an inside-out DC motor without brushes (hence "brushless&quot, it is made with the fields (permanent magnets) on the shaft and the "armature" on the outside (stator). In order for the motor to have the same speed/torque characteristics as a DC motor, then it has to be commutated based on the position of the "armature" windings relative to the field poles. This means that the controller has to switch voltage between the three incoming power leads based on shaft POSITION, not speed. Speed is controlled as a separate issue. While a standard inverter is the same basic construction as a brushless drive (three motor leads, capacitor bank, 6 power transistors), the output is controlled in a different sequence that a standard induction motor.

ABB ACS 601 will run this motor if used with an encoder and the brushless firmware is loaded. The Yaskawa G5 drive will run this motor if the firmware is changed (making it a PS5) and the tach feedback or resolver feedback card is added. The Siemens Master Drive with MC regulator will run it, TB Woods Vector drive will run it, Control Techniques Unidrive will run it, and many others.

Regards
GusD'



GusD

 

[Skogsgurra]

OK GusD,

First: I did not know about that possibility (reconfiguring an VFD to run BLDC). So you added to my "awareness base".

Second: I work mostly with classic drives i.e. standard asynchronous motors w/ or w/o encoders or DC motors with brushes and a collector. So I almost never think BLDC when I read DC motor. And I still do not know if bottler meant "pure" DC or BLDC.

bottler: Are we helping? Or do you just get confused? If so, remember that confusion is the first step on the road to knowledge.

 

[GusD]

HELLO bottler

and to Skogsgurra as well.
You kind of made my morning with your little piece of wisdom "confusion is the first step on the road to knowledge".

Thanks for the advice.I am sure I'll use it ,at least once today.

GusD

 

[ScottyUK]

GusD,

In the same vein:

Experience is what helps us make a new mistake each time.
And if we learn from our mistakes, I guess I'm getting a great education!

regards,


Scotty.

 

[jbartos]

Suggestion: Visit

http://search.abb.com/library/ABBLi...ageCode=en&DocumentPartID=1 / 1&Action=Launch

for AC Drives
and then download a DC drive from the same ABB site:
"DCS Thyristor power converter for DC drive systems 20 to 1000 A 9 to 522 kW Manual DCS 400", for example.
Compare those two drives to see the differences.
If there is a need for a dedicated DC drive for DC motor, it is better to have it DC since there will not be parts needed for AC, and vice-versa. If there is a need for having a universal drive, AC and DC, then the choice is clear. There are other factors that are often taken into consideration and not mentioned in the above postings, e.g. cost, reliability (MTBF, MTTR, etc.), Life-Cycle, etc.