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First known VFD's

First known VFD's

First known VFD's

Does anyone have the history of variable speed AC motors? Who, when, where and what size?

RE: First known VFD's

Depends on how you define "VFD". The first known PWM drive, although not made commercially available, was developed at Stromberg Electric (Finland) in 1960 as an early experiment in what the new "transistor" could be used for with regard to motors. Stromberg was a huge source of early industrial electronics research at that time and although they made products that basically sustained them, their real focus was on innovation. So they didn't actually put one into use until 1972/3 for the Helsinki Metro and it was a big huge MV motor drive.

In between that time (through the 1960s) there were several basically simultaneous developments of commercially available "6 step inverter" drives, both Voltage Source and Current Source from Westinghouse, Borg Warner, GE and Emerson, all in response to a project started by DuPont for ways to control AC motor speeds for textile fiber manufacturing, because DC motors were problematic in fiber production facilities. They all used SCR / GTO thyristor technology with different methods of controlling voltage and although functional, were not very motor friendly. Motors and drives had to be "matched", so if you changed out either one, a technician had to be called in to match them up again. That slowed the acceptance of the technology quite a bit.

The first commercially available low voltage PWM VSI drives as we know them today were released in Europe by Stromberg in the mid 1980s, and in the US from a company called Parametrics in Connecticut, followed a few years later by Stromberg licensing drives to Allen Bradley in the US. But the "big boom" in the early 1990s for VFD technology world wide was ignited by the low cost compact designs that came out of Japan from Toshiba, Yaskawa and Mitsubishi and all of the 6-step thyristor based drives almost immediately were sidelined by 1995, because PWM VSI drives could be used on any motor (within reason). After the Japanese drive revolution, both Stromberg and Parametrics faded into the background and eventually became rolled into what is now ABB, then people like Allen Bradley, Siemens and Emerson developed their own PWM drive products, while other big electrical suppliers like Square D, Cutler Hammer and GE went the route of brand-labeling theirs from other suppliers.

" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

RE: First known VFD's

You can read a lot about this in a book called "SAMIN tarina" by Martti Harmoinen, the Finnish engineer who worked at Stromberg on the first PWM drives (SAMI was the name of their product, named for the indigenous people of Lapland, part of Northern Finland, Norway and Sweden).

" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

RE: First known VFD's

First drives I saw were Baldors. Do you know where they fit into that evolution Jeff?

Keith Cress
kcress - http://www.flaminsystems.com

RE: First known VFD's

Technically, the first "variable speed" motor was invented by Nikolai Tesla in 1888. It was the general-purpose squirrel cage induction motor. The rotational speed can vary with the application of load, as slip frequency changes - even if the line frequency remains constant.

I think what you're really trying to get at is when was the first ADJUSTABLE SPEED drive/motor combination created.

The difference is that with adjustable speed, the speed can be held constant (at any point in the operating range) regardless of load; for variable speed, the amount of load impacts the operating speed.

Converting energy to motion for more than half a century

RE: First known VFD's

I was thinking about mentioning that there are many variants of AC motors that are capable of variable speed operation,
Gr8blu beat me to it.
Early rail traction drives used 3 phase motors, changing speeds by changing the number of poles in the motors.
Later traction drives used single phase AC 16 2/3 Hz or 25 Hz, and motors that resemble universal motors, speed is adjusted by adjusting the terminal voltage. Either resistive control or multi tap transformer.
There were also examples that used 3 phase traction motors driven from a motor generator set having the ability of having a variable Hz output.
There are also examples of slip ring and commutator motors that adjust speed by changing rotor resistance or shifting brush position.

Quote (Audel's New Electric Enclopedia)

RE: First known VFD's

Thank you all for the information.

RE: First known VFD's

Quote (itsmoked)

First drives I saw were Baldors. Do you know where they fit into that evolution Jeff?
Yes, as a matter of fact I do. The original Baldor drives (so likely what you saw maybe in the early 90s?), was made by a company in Seattle called Sweo Engineering. I was living there at the time and almost went to work for them. Sweo made Regenerative DC drives for the lumber industry in the 80s, but branched out into doing servo drives and eventually vector AC drives starting around 1990, so early on in the drives boom, but limited by their being a very small company (<12 employees when I talked to them). Baldor started brand-labeling their drives some time in the mid 90s and eventually bought the company from Ed Sweo in 1998. But baldor in their infinite wisdom moved it lock-stock and barrel to Ft. Smith Arkansas, losing about 90% of their engineering talent in the process because people who are used to living and working in Seattle did not like the idea of going to Arkansas. That started the decline of Baldor's VFD market share that continued until ABB bought them (for the motors) and shuttered the entire VFD operation in favor of their own. I think there is still a "Baldor" drive, but it is an ABB drive with a Baldor graphic on the front.

" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

RE: First known VFD's

Ahhh fascinating.


infinite wisdom moved it lock-stock and barrel to Ft. Smith Arkansas

Classic pre-Covid corporate thinking!

Thanks Jeff!

Keith Cress
kcress - http://www.flaminsystems.com

RE: First known VFD's

It's amazing that I came across this thread, and the mention of Sweo Drives.
The machine shop I worked at had a couple machines which had been retrofitted with upgraded Dynapath CNC controls.
The failure point after the retrofit was the 10hp DC spindle motor which was installed.
In a production environment, the PM DC motors couldn't take what we demanded from them.
We were constantly replacing brushes and cleaning commutators. They eventually went up in smoke.
The DC drives used happened to be made by SWEO, which happened to be local company. The machine shop was in Auburn, WA., and Sweo was in Bellevue.
We contacted Sweo, and they advised us to get specially balanced Inverter Rated 10hp AC motors with encoders utilizing their new 'Flux Vector' drive.
Once we completed the conversion, we were quite pleased with the results, but were having trouble getting the full 10hp out of the motors.
Sweo was extremely helpful, and actually sent the engineer (His last name was Olmstead, all I remember!) that designed the 'Flux Vector' drive to assist in troubleshooting.
Olmstead and another engineer that came with him spent the day there, analyzing what the drive was doing under a full load, altering various parameters.
They were quite excited (especially Olmstead!) for the opportunity to play with their 'toy', the Flux Vector drive, and see it operating under full load conditions 'in the field'.
By the end of the day, they concluded that we needed to feed just a little more voltage to the drive, which we did with a 3 phase transformer. Problem solved!
All in all, it was a really fun day, and I felt quite privileged for the opportunity to assist the guy that designed the drive!

RE: First known VFD's

If you didn't know, some of the engineers from Sweo that didn't move to Arkansas started a new company in Redmond WA that services the old Sweo and Baldor drives and servos.

" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

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