Environmental Engineering Reference
In-Depth Information
Square wave
oscillation
Harmonics
Fundamental frequency
Figure 4.55
Construction of a Square-wave Oscillation from Different
Sinusoidal Harmonics
(4.117)
Most national regulations or grid operator requirements lay down maxima for
the current harmonics. Inverters can cause voltage harmonics in addition to
current harmonics. These are also limited by maximal permissible values in
relation to the first harmonic. The
harmonic distortion factor
(4.118)
which is calculated using the voltage harmonic amplitudes
^
n
and the first
harmonic amplitude
^
n
, describes the harmonic content of the voltage. The
maximal permissible harmonic distortion factor is usually
D
= 0.8. Besides
the amplitudes, root mean square (rms) values are often used for calculations.
In Chapter 5, the section headed 'Alternating current (p205) describes the
calculation of rms values in detail.
Another quantity of assessment is the
relative harmonic content
,
(4.119)
which is the ratio of all the rms harmonics except for the first one to all the
rms harmonics. The relative harmonic content for good inverters is below 3
per cent. If the harmonic content is too high, filters must reduce it.
