Questions about Variable Frequency Drive (VFD)

[anggoro_yn]

Variable Frequency Drive

Hi all,

We all know that VFD change the frequency of our main electrical supply to a specified frequency according to our necessities.

Why every VFD always change the AC current to DC (rectify the current) in the first stage and then convert it back to AC current in a specified frequency (the frequency that we need)?

Can we convert the frequency directly from the main line frequency to the specified frequency without having to rectify the supply first? Is there any device (gate, transistor, transformer, etc) that can convert frequency?

Thank you.

aaNg

 

[Davood Amerion]

Variable Frequency Drive

No, but in old system it can be done with cycloconvertor. it use some of semiconductor (trystor) and produce frequency smaler than input.
but output frequency had some of harmonic.
cycloconvertor now obsoleted.

Regards
Davood

 

[echo47]

Variable Frequency Drive

If you want to convert between common frequencies such as 50, 60, or 400 hertz, then a rotary frequency converter (motor-generator) works great.

Example products:
**broken link removed**

Comparison between rotary and solid-state:
**broken link removed**

 

[anggoro_yn]

Re: Variable Frequency Drive

What about the price? The site do not mention about the price. Is it far more financially effective to use conventional VFD or the ones that you all mentioned?

aaNg
PS: I have worked in two different companies (mining and pharmaceutical manufacturing), but I always see normal VFD.

 

[epp]

Re: Variable Frequency Drive

VFD are cheaper now and are used in many appliactions. You have to rectify AC to DC in order to have better control of output current, voltage, frequency and torque with improved: ripple, EMI, noise etc. - characteristics.

Cycloconvertors make direct AC-AC conversion and you can find sth inetersting in
www.ipes.ethz.ch about it and about some other converters. prof. Johann W. Kolar invented some kind of matrix converter which makes acac conversion. Find his papers.

Regrads.