HARMONICS Measurement

[rashu]

to design an VI such that we can vary % of harmonics injecting to the fundamental wave

1) fundamental, pure sine wave= 50hz
 
2) harmonics injected= 100 hz ( ie, 1st harmonic)  ( harmonics is the integral multiple of fundamental wave)
 
then we add both pure and harmonic , to get combination = distortion ( shown in gragh as combination)
 
then we pass through filter, and reproduce pure sine wave.
 
now here,, next step is to find out how much % of harmonic has to be injected to get the distortion,
 
ie.., 1% of 100hz= does not make any change
 
       10% 100hz = some changes
         30% of 100hz = some more changes in distortion
       40% of 100 hz   =    more changes
 
here now to design to specify  these  % of harmonic injection????????
like supose we want to send only 10 % of 100hz harmonic frequency,
 
 
 

[Joe_S]

Hello pruthvi,

I'm afraid I need a little more clarification of what you are hoping to do.  What is it that you are trying to have happen?  When you say adding a % of a harmonic, do you mean a % of the frequency or of the amplitude?  And is this more of a theory question or a LabView question?

Regards,

Joe S.

[rashu]

DEAR SIR,

thanks for reply

its more of practical implementation

its adding frequency,

if   1) fundamental frequency = 50hz

2) harmonic = 1st harmonic 100hz

but we need to design such that we should apply 10 % of 100 hz

                                                                 then, 20 % of 100 hz

                                                                 then 30% of `100hz.... so on..

now in this VI i have designed such we can apply whole 100hz once,, not each indiviual % of 100 hz

kindly give some inputs how to design such that we can apply 10% or 20% or 30 % or 40 % of 100hz.

kindly reply

thank you

[johnsold]

Multiply the 100 Hz signal by 0.1, 0.2, ... before adding it to the other harmonics.

Phase shift is more difficult.

Lynn

[rashu]

dear sir,,

the sugession which u gave,, really worked,, but the thing is ,, i have to recollect the %THD, which we have given in the input,,

fundamental frequency= 50hz

harmonic=  100 hz

10 % of 100hz= 100 * 0.1 = harmonic input

 fundamental + harmonic ( 10% of 100hz) = harmonic diatortion

in the harmonic distortion we need to indicate same 10% harmonic has detected,

concept is  after injecting the harmonics from the input side to fundamental sine wave=> we need to detect that same harmonic %  from distortion.

 i have tried  harmonic distortion analyzier icon to measure the THD,, but i could not succed to get exact % of harmonics as we have given in input.

i have attached my revised VI with this , kindly check

 

[rashu]

we have filter the harmonic distortion to reproduce the pure fundamental sine wave.

by appling iir filter coefficients to the rms value of the harmonic distortion using arithmetic operators, we have to filter the harmonics and get back pure fundamnetal signal

suppose fundqamental =60hz==> rms= 240 volts

fundamental+ 1st harmonic+2nd harmonic+3rd harmonic=harmonic distortion =259volts or 270volts( depending on number of harmonics added)

we need to filter this distortion 259volts to get back 240volts appling filter coefficients on this voltage.

iir filter have reverse and farword coefficients.

kindly give me an idea how can i filter these distortion using coefficients.

coefficients-- rev . coefficients== -3.2454, 4.356, 3.0034, 0.0234

                  fwd coefficients= 0.0113, 00000,0.0234,0000,0.01115

[johnsold]

Your requirements seem to being changing continually.

What definition of THD are you using?  Several different definitions have been used and they are not all equivalent.

How did you select those coefficients?  What is the specified filter characteristic?

Lynn

[rashu]

ya i agree with u sir,

my project has taken litle divviation

since i am designing in lab view, later it has to me implemented in microprocessor. it has to be in basic design.

there are direct icons in lab view, such as IIR CASCADE FILTER, which will use filter coefficients and input signal and filters the signal and gives only output

as fundamental.

but practically we can not implement this icons,

'

by using only arithmetic and trignometric operators we need to design a filter that will filter the distortion and get the filtered pure fundamental value.

[rashu]

THD%= SQRT( H1 SQRE+ H2 SQURE+---------------------------+HnSQR)

                _________________________________________

                                     H1

THIS formula iam usng this formula.

i have designed this formula in labview.

now i need to use filter coeffiecints to filter the distortion by using arithmetic and trignometric operators.

or else

can u suggest me any method of designing filter with only arithmetic opeators and trignometric operators.

 now main purpose is to design a filter that  filters out the distortion of any number of harmonics H1+H1+H3------------ and finally gives pure fundamental sine wave.

[rashu]

IIR Cascade Filter with I.C. (DBL) this icon in the lab view, filters the harmonic distortion by using the filter coefficients, can any 1 tell me how does this icon work, whats the internal logic behind this, i have uploded  picture of this icon, i have searched in ggogle i am not getting.

kindly reply

thanking you

rashmi