# Harmonics in power system [closed]

I have seen in some text books that power converters produce harmonics in power systems.

How do power converters inject harmonics in a power system?

## closed as too broad by Finbarr, Voltage Spike, JYelton, Dmitry Grigoryev, Phil GJun 7 at 21:37

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• All power converters to DC use pulse currents and all pulses contain harmonics The common mode LC line filter reduces the harmonics conducted on the line but the neutral harmonics tend to add from cumulative sources of "Triplen" 3^n order harmonics and result in high neutral currents which are bad for Y transformer windings unless oversized. electronics-tutorials.ws/accircuits/harmonics.html – Tony Stewart Sunnyskyguy EE75 Apr 28 at 15:51

Figure 1. A three-phase rectifier and resultant waveforms. Source: Invertek.

• Power converters use diodes to rectify the AC supply and feed the internal DC link.
• The rectification causes non-sinusoidal current waveforms. See Figure 1.
• Any repeating waveform can be constructed from a series of sines of integer multiples of the fundemental frequency of the waveform. These are the harmonics.

Figure 2. This fabulous illustration of the Fourier Transform by Lucas V. Barbosa on Wikipedia's Fourier transform page shows the transformation of a periodic waveform from the time domain to the frequency domain. The frequency plot shows the relative strength of the harmonics with clarity that could not be obtained from staring at the time plot.

• It should be apparent that the more square the time domain waveform is then the more harmonics you will have and these should be visible in the frequency domain.

How does power converters inject harmonics in power system?

It is because of the non-sinusoidal current waveforms caused by the rectifier diodes.

A perfectly resistive load will draw sinusoidal currents. Anything non-linear like a bridge rectifier with filter cap, or even a non-perfectly corrected supply with PFC, will draw currents that are not perfectly sinusoidal. Since the impedance of a power system is not constant, that results in non-sinusoidal currents that consist of a fundamental frequency and a number of harmonics.

See This answer. You could also find out a lot with Google and searching other answers in this forum.