Figure 16 - Typical diagram of a VFD
Figure 17 - Harmonics on the grid
Since the rectifier bridge sees before it a direct current stage, the current taken is practically in phase with the voltage.
NO
because the harmonic components in excess of the fundamental harmonic do not contribute to the active power. Several
values therefore need to be defined:
Displacement Power Factor
However, the formula below no longer applies
cos
3
I
V
P
act
cos
DPF
Power Factor (total power)
DPF
I
I
PF
1
The Power Factor takes into account both phase displacement as well as harmonic content, expressed as a ratio of the
fundamental component I
1
to the current and the overall effective value. It actually expresses which part of the input
current is converted into active power. It is worth mentioning that in the absence of an inverter or electronic devices in
general, the DPF and PF are the same.
Moreover, many electricity boards only take into account the DPF, since the harmonic content is not measured, but only
the absorption of active and reactive power.
Another measuring index for the harmonics in the grid is provided by the harmonic distortion coefficient THD
i
(Total
Harmonic Distortion):
2
1
2
1
2
I
I
I
THD
i
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Summary of Contents for EWYD-BZ Series
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