how to find harmonics in dc?

[manohar.k]

I want to know the percent of harmonics that are present in system when ac is converted into dc?

 

[FvM]

The question isn't very clear. By definition, harmonics only exist for AC systems, so I presume you are asking for harmonics on the AC input? AC power supply is a low impedance voltage source in a first order, thus we are looking at harmonic currents.

The current waveform and respective harmonic content strongly depends on the AC/DC converter (e.g. rectifier) circuit and its parameters and to a certain degree also on the mains impedance.

If you are asking about specific converter/rectifier circuits, you should specify it.

 

[andre_luis]

If you are talking about to take the frequency spectrum of a signal composed by AC and DC components, there should be no procedural difference on how to obtain in whatever the signal frequency. Note that the DC component is a particular case of an AC component, whose frequency is equal to zero.

In general you can employ a FFT algorithm for that.

 

[jamesd168]

I want to know the percent of harmonics that are present in system when ac is converted into dc?

you can use a fluke energy analyzer, it will automatically give you the harmonics.

 

[jiripolivka]

As DC is rectified from AC and low-pass filtered, you can determine any AC component remnant by using a better low-pass filter.
THe question rather should be: what harmonics can be a problem in what DC-powered system?

 

[andre_luis]

I want to know the percent of harmonics that are present in system when ac is converted into dc?

Reviewing the question from a more practical point of view, I believe that the real issue is more likely to know how to obtain a method to measure the degree of distortion of an AC voltage due to the effect of flattening of the peak of the sine wave when subjected to a standard rectifier, that due to the filtering capacitor, restricts the entire recharge to just a short period immediately before the peak of the wave.

 

[vikasbly44]

DEAR...
AC power supply is a low impedance voltage source in a first order, thus we are looking at harmonic currents....

The DC component is a particular case of an AC component, whose frequency is equal to zero.