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# low cost Harmonic filter at VFD's input

Can any body has idea to design low cost Harmonic filter to be connected at the input of drive and sinus filter for drive pwm o/p? Need the factors to consider while designing.

#1

09-17-2013 06:53 AM

Top #2

What is the requirement, IEEE-519?

09-17-2013 09:17 AM

Top #3

It depends on the specific converter topology in the drive you are currently using. For common 6-pulse diode front-end rectifier, a 3-phase line reactor (e.g, 3% per unit) is the most simple approach to meet the harmonic restriction posed by IEEE std 519-1992. For the drive output filter, you could design a passive LC filter, but you need to consider the switching frequency f_sw, fundamental frequency f_0, as well as the losses across the filter. As a rule of thumb, for a sinewave filter, the LC parameters should meet: f0<1/[2*pi*sqrt(LC)]<f_sw, as as to avoid resonance with the ac drive and load. The specific LC value can be determined by minimizing losses when tune the LC filter.

09-17-2013 12:02 PM

Top #4

What is the requirement of IEE -519? On what basis calculation is done that 3% line reactor is sufficient to meet IEE -519? As per IEC -519 what should be the Voltage harmonic and what should be the current harmonic?

09-17-2013 02:22 PM

Top #5

Hi Rohit, the IEEE std 519-1992 can be found in the following web link, in which the limitations for THD-Voltage and THD-Current are elaborated. To reduce the harmonics within the limits recommended by IEEE 519, a LC harmonic trap filter can be designed and connected behind the line reactors (inductors and capacitors are connected in series, and serve as a shunt device to the ac supply). For example, if 5th harmonic are the dominating components contributing to the distortion, then try to tune the LC resonate frequency around 5*f_fund, so as to provide a low impedance path at the selected frequency. Since much of the harmonic current demanded by the load now comes from the trap filter, the harmonic current distortion will be reduced. Of course, there are some other harmonic filtering approaches, but LC trap filter is the least complicated one. Hope it helps.

http://www-ppd.fnal.gov/eedoffice-w/infrastructure_group/huffman/web/engineering/standards%5CIEEE519.pdfhttp://www.transcoil.com/Public/Documents/TechnicalPapers/meetieee.pdfhttp://ewh.ieee.org/r3/atlanta/ias/IEEE_519.pdf

http://www-ppd.fnal.gov/eedoffice-w/infrastructure_group/huffman/web/engineering/standards%5CIEEE519.pdfhttp://www.transcoil.com/Public/Documents/TechnicalPapers/meetieee.pdfhttp://ewh.ieee.org/r3/atlanta/ias/IEEE_519.pdf

09-17-2013 05:20 PM

Top #6

Thanks

09-17-2013 07:25 PM

Top #7

Great answer Jiangbiao!

As far as cost it is cheaper to tune out higher frequencies because there are fewer turns of copper wire. If you can increase your carrier frequency you can save money on the filter. There is a point where a higher carrier frequency causes a de-rating. Larger motors like a lower carrier frequency. The de-ratings should be in the inverter manual.

As far as cost it is cheaper to tune out higher frequencies because there are fewer turns of copper wire. If you can increase your carrier frequency you can save money on the filter. There is a point where a higher carrier frequency causes a de-rating. Larger motors like a lower carrier frequency. The de-ratings should be in the inverter manual.