VSD VFD???? again 1

[justlearning2]

Hi
Could someone please tell me the difference between VSD's and VFD's.
Is it that VSD are for DC and VFD are for AC.
How do they operate?
All help is welcome.
Thanks in advance,
Brendan
Hopefully my stay in this forum will longer this time.

 

[dpc]

These terms are, regrettably, used interchangeably. To be precise, a Variable Speed Drive (VSD) is a more general term and applies to ANY drive that is capable of varying the speed of the output shaft to some piece of drive equipment. So a dc drive, an AC adjustable frequency drive and an eddy-current drives are ALL VSD's, at least in my opinion.

A variable frequency drive (VFD)is a drive used to vary the speed of an ac motor by means of converting the incoming mains power to a differing frequency. It applies to ac motor drives, both induction and synchronous.

To be even pickier, I believe the preferred IEEE/NEMA terminology for "Variable" frequency drives is actually "Adjustable Frequency Drives" or ASD's. This is a slightly more accurate description, since it implies an intentional adjustment of frequency. But "VFD" is in common use, no question, and has a long tradition of related terms, such as Variable Frequency Oscillator (VFO), etc...

OK, back in my hole...

 

[jbartos]

Suggestion: Reference:
1. IEEE Std 100-2000 "Dictionary"
1a. VSD is an electric drive so designed that the speed varies through a considerable range as a function of load.
(No mention of type of motor.)
1b. VFD is not cited in Reference 1. The VFD varies the frequency of the power supply, among other variables, to obtain variable frequency output for AC motors and potentially other type of AC loads that may need a variable frequency power supply.

 

[jbartos]

Suggestion: Visit

http://www.system-directions.com/prod02.htm

http://www.caconline.com/Solutions/CAC/Controllers_CAC_EXS-1000_Pump_Off_Controller_VSD.html

http://www.control.com/topic_articles_page?use_category=motion_cat&query_start=101

etc. for more info

 

[jraef]

In an effort to add confusion to dpc's explaination, I also have heard several salesmen at PT houses refer to mechanical variable speed drives using variable pitch pulleys as VSD's, and technically they would be correct (notwithstanding jbartos' IEEE definition, which would not consider mechanical devices).

We love to use TLA's (Three Letter Acronyms) to descibe things, but sometimes they can lead to unwarranted confusion. I once was involved in an energy optimization contract and I wrote in a summary report that the owner follow up on a list of items, including "VFD for air handler". He immediately called the air handler service tech, explaining that I had uncovered a potential fire hazzard. The service tech found nothing wrong and called me about what I had found. After a lot of head scratching we figured out that to the owner, VFD was what he used to describe the local Volunteer Fire Department!

Another common mistake is to refer to AC AFDs as "Inverters". There is AN inverter IN them, but technically that is only 1/2 of the system or less if you count the adjustable part. When you get into the off-grid or marine power systems business, an Inverter is just that, it only converts the DC supply to an AC sine wave. Subvert the dominant paradigm... Think first, then act!

 

[jOmega]

jraef,
As long as you are trying to walk the straight line, then consider...... that an inverter INVERTS dc to AC ...
CONVERTER converts AC to DC.

And as to your statement about the inverter being only half of the system.... I can't seem to rationalize this statement when considering inverters that operate of common DC busses.... or off Battery Busses.... i.e. UPS systems operating from a battery supply, does not contain the Converter section .... ergo, the inverter is the whole...And as far as the AC motor is concerned, only the Inverter is of importance.... it doesn't care if the dc bus comes from a diode bridge, an scr bridge, a pwm chopper, a battery pack, or a dc generator. Just as the muzzle is the business end of a .357 magnum, so to is the INVERTER the business end of a VFD or AFD or Inverter, or whatever plucks your harp ...

..."a rose by any other name....." etc. is still a rose.

Cheers

 

[jraef]

jOmega

"As long as you are trying to walk the straight line, then consider...... that an inverter INVERTS dc to AC ...
CONVERTER converts AC to DC."

My bad.


As to the other point, do you then refer to all .357 magnums as "muzzles"? That IMHO would be the same as referring to AFDs as Inverters. My point was akin to the "square vs rectangle" issue. Every AFD has an Inverter, but not every Inverter is an AFD. I think we are saying the same thing, but I apparently didn't get my point across correctly the first time.

At least "Inverter" is better than the one I heard last week where a customer was refering to one as "that motor speed controller dohicky". Subvert the dominant paradigm... Think first, then act!

 

[peebee]

I also disagree with your terminology, j0mega.

In my opinion, the term "UPS" implies both a rectifier and an inverter.

A device which takes a DC source and converts it to AC, but does not contain a rectifier is known as an "inverter", not a "UPS".

Similarly, it would be improper to refer to a VSD/AFD/VFD as an "inverter".

 

[jOmega]

Dear Peebee,

You certainly have every right to disagree. And as you stated, .........

Peebee said:
[red]"In my opinion, the term "UPS" implies both a rectifier and an inverter."[/red]

Over the last 40 years, I've designed, built, installed, many UPS systems that consisted of a Battery cabinet, a battery charger, an Inverter, and a transformer,

Many are still in operation today.

Common applications are for Emergency Lighting.

Could I change your conviction if I were to share with you, the definition of a UPS taken from the IEEE Standard Dictionary of Electrical and Electronic Terms ?

Ok? Here goes.

uninterruptible power supply module (UPS) (emergency and standby power).
A system designed to automatically provide power, without delay or transients, during any period when the normal power supply is incapable of performing acceptably.[/b]
446-1987
(2) (electric power systems in commercial buildings).
A device or system that provides quality and continuity of an ac power source. 241-1990

uninterruptible power supply module (UPS module) (electric power systems in commercial buildings).
The power conversion portion of the uninterruptible power system. 241-1990

Note that it does not say that a UPS has to have a rectifier section for the conversion of AC to DC ... A battery pack is perfectly within the definition.

//

 

[peebee]

Peebee said:
"In my opinion, the term "UPS" implies both a rectifier and an inverter."

jOmega said:
Over the last 40 years, I've designed, built, installed, many UPS systems that consisted of a Battery cabinet, a battery charger, an Inverter, and a transformer,

Well, your charger is a rectifier. I agree that you built a UPS. It included both a charger and a rectifier. I see no conflict.

An inverter does not meet the requirements of your second posted definition: "A device or system that provides quality and continuity of an ac power source." An inverter alone will not do that. It requires a DC converter and energy storage to meet that definition.

A UPS is is an AC/AC converter with energy storage. An inverter does not qualify, although inverters are used in many UPS configurations. There are also other configurations which do not use inverters, such as motor-generator sets.

An inverter is only half of a double-conversion UPS system (or only one-third if you count the batteries).

 

[peebee]

Typo:

I meant "It included both a rectifier and an inverter"

 

[jOmega]

Ahhh Peebee,

The rectifier is not part of the power conversion. It is there ONLY to replenish the dc source when the inverter is off line. After all, when the ac line power disappears, is it your belief that the "charger rectifier" is involved in the sourcing of AC to the load ?

If so, you must tell us all how this is possible with no input to that function!


In your opinion, a UPS is an AC to AC converter. Seems you and IEEE are in total disagreement.

Also, the laws of physics are in danger of being repealed if you continue to insist that a UPS has an AC to AC involvement.

When the ac line power disappears, does not the input AC disappear.... and then is it not just a relationship between the batteries and the inverter. The inverter inverts the DC from the batteries to AC ?

I sense that will never change your belief, and so, further discussion is of little value and a waste of bandwidth.

I'll stick with the laws of physics and the IEEE.
Oh, FYI, I'm working on a design that uses a fuel cell to provide the DC power for the "INVERTER". No battery, No AC to DC conversion or Battery charger.

Perhaps you'd care to suggest a name for this product since it obviously doesn't conform to your definition of a "UPS" .

 

[peebee]

Your fuel cell system already has a name: fuel cell and inverter.

This system does not meet your definition of a UPS system: "A device or system that provides quality and continuity of an ac power source." All definitions I've posted strictly conform to this, so I don't see how I'm in any disagreement with IEEE.

Please explain how anything I've said goes against the laws of physics.

Your fuel cell system has no AC power source; it IS the AC power source.

Conceptually, your fuel cell system is not much different than using a gas-fired reciprocating generator for prime on-site generation as an AC source. No-one would call a generator a UPS, they would call it an AC source, regardless of how reliable it is. Neither would they call a DC generator with an inverter a UPS, they'd call that a DC generator and an inverter.

Similarly, but conversely, no-one would call the "alternator, voltage regulator/rectifier, and battery system" in a car anything but just that.

 

[peebee]

By the way, jO, you got me thinking about fuel cells, and I posted my thoughts on them: thread804-39066 . I invite you to comment.

 

[jbartos]

Suggestion: With the power electronics strong evolution, the traditional Converter from AC to DC is now much broadened, e.g. Converter AC-DC-AC, AC-AC, and DC-DC. However, the Inverter tends to stay and represent DC-AC conversion.

 

[jOmega]

JBartos:

DC-AC inversion ??? ergo the term : Inverter.

 

[jraef]

Somebody call out the VFD (Volunteer Fire Dept.) and cool these guys off!

Quando Omni Flunkus Moritati

 

[jbartos]

Suggestion to jOmega: There are many books written and many courses offered on the energy conversion. Therefore, an energy converter is often considered as the general term including rectification, inversion, step-down or -up transformation, etc. It just depends where one is coming from to the energy conversion.
To stay up to date, visit

http://www.xootr.com.au/news/news090302_2.htm

for a Pro-Drive Electric Conversion Kit

 

[jOmega]

Jbartos:

Let's see... another obscure and irrelevant reference you bring us once again.

'twould seem to be your opinion sir. I prefer to align my beliefs with the definitions as stated in the IEEE Dictionary; which defines converter as that which changes AC into DC ... and an Inverter as that which changes DC to AC.

It is not uncommon, JB, to find terminology mis-used by people who mean well, but are either ill-informed or ill-advised. When we give new meanings to established or standardized terms, we begin a process that impedes our ability to communicate with others. "Huh, What'd he say ? " or "I wonder what he meant by that"... Suppose that instead of referring to a converter as the first state of a voltage source VFD, we call it a "thing-a-ma-bob" or "thingy" for short... So now all THINGYs cannote a device that changes AC to DC.... ?
But then I heard a girl on TV the other nite referring to the electric starter in her car as a "thingy" ... so it must be that VFD's also have electric starter motors.

You can then see from the foregoing, how quickly intelligent and informative communication would degenerate into the non-sensical.

It's a converter, JB, that is the first stage of a VFD that operates from the AC Mains..... Not an energy pak for a bicycle.

 

[jOmega]

Jraef ...

Harry Truman once said: "If you can't stand the heat, get out of the kitchen."