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lasam
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Join Date: Apr 2009
Posts: 10

VFD and Pulse

08/02/2009 8:53 PM

The VFD's are characterized as 6-pulse, 12-pulse, 18-pulse, 24-pulse etc. What are these pulses? Why they are multiples of 6? Is more the pulse number, the better the VFD's? How does the pulses affect on THD? Please explain
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jack of all trades
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#1

Re: VFD and Pulse

08/02/2009 9:45 PM

Try the following link.

http://en.wikipedia.org/wiki/Variable-frequency_drive

and the 'three phase' and 'rectifier and inverter pulse number' sections of the following link regarding the multiples of 6 switches (which are necessary for switching three phase to create a pulse-width output signal). From the link below,

circuits that have a higher pulse number have reduced harmonic content in the AC input current and reduced ripple in the DC output voltage

http://en.wikipedia.org/wiki/Inverter_(electrical)

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msamad
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Join Date: Feb 2009
Location: Houston, USA
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#2
In reply to #1

Re: VFD and Pulse

08/02/2009 10:17 PM

Please read the "Chapter 7 - How to reduce harmonics by structural modifications in the AC drive system" (page 17 to page 23) from the ABB documents available in the link below:

http://library.abb.com/global/scot/scot201.nsf/veritydisplay/518a84b65bb2ff40c1256d280083acbd/$File/Technical_Guide6_EN.pdf

and you will get all your answers.

- MS

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