synchro
Senior Member
- Location
- Chicago, IL
- Occupation
- EE
The only thing which I am not able to understand is that how a 6 pulse VFD automatically removes the 3rd harmonic ?
Getting back to the basics, first of all there are no even harmonics in the VFD input currents because it's a full-wave rectifier.Also as there is no triplen harmonic in VFD circuits, so in which circuits does the triplen harmonic exist?
There can be no triplen harmonic currents because as Hv&Lv mentioned these are zero sequence currents and would therefore require a neutral connection for them to be conducted. A 3-phase 6-diode bridge in a VFD does not have a neutral connection.
So if we eliminate the triplens (all odd multiples of the third harmonic: 3rd, 9th, 15th, 21st, ...) then we are left with the 5th, 7th, 11th, 13th, 17th, 19th, 23rd, etc. So as Besoeker3 mentioned these are at harmonic numbers n = 6k+-1, where 6k-1 are negative sequence and 6k+1 are positive sequence.