Non Standard Inverter Design

[Dobber1978]

I have an idea, just want someone to tell me why it's a bad idea.

I am thinking about an inverter design that does not use solid state but using a DC motor turning a AC generator. Need more out you increase the current to DC motor to increase the torque to increase the output power.

The two biggest problem I could think about with this design was that;
1. Would be bigger, physically then a solid state inverter
2. Effecency would not be as good as solid state.

How else does this design fail???

 

[Skogsgurra]

The design wouldn't fail at all. That's the way many variable frequency drives were built 30+ years ago. I have run test stands for high-speed compressors using just that kind of equipment.

The reasons things aren't done that way any more are many. Economy, control flexibility, maintenance, life of brushes and commutator, efficiency, foot-print, need for cooling and stable foundations are the more important reasons that made solid state technology take over.

Gunnar Englund

http://www.gke.org

 

[Blackcountryman]

I feel old when I see the technology I cut my teeth on being re-invented.

It's happening too often these days.

John

 

[jraef]

Dobber1978,
Google "MG Set", or "motor-generator set" or motor-gen set". They were the primary means of varying speed or AC power a long time ago. They were used a lot on Navy vessels, and after WWII a lot of them ended up in industry here in the US because they were cheap surplus equipment. They ended up in sawmills, conveyors, cranes, everywhere that needed variable speed control. But in terms of all the things you listed as potential drawbacks, they would all be true compared to solid state. Thats why they have become rare now.

Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[spargher]

Have you ever heard about the "Ward - Leonard" configuration?

Just do a google search...

We use daily this system when testing our motors. It is convenient because we can easily adjust the frequenct, start the motor at slow speed and it is also possible to change voltage settings acting on generator connections (wye - star - double star - etc...)

Some year ago we als built some 50 - 60 Hz frequncy converters using two syncronous machines coupled toegheter, one 10 poles was driving a 12 poles at fixed speed (the 10 poles motor runs at 600rpm when feedet at 50Hz and drives a 12 poles generator which generate a 60Hz power)