2-27
D Causes of Harmonics Generation
•Usually, electric
machines have built-in circuitry that converts commercial AC power
supply into DC power.
Such
AC power
, however
, contains
harmonics due to the dif
ference in current flow be
-
tween DC and AC.
Obtaining DC from AC Using Rectifiers and Capacitors
DC
voltage is obtained by converting AC voltage into a pulsating one-side voltage with
rectifiers
and smoothing the pulsating one-side voltage with capacitors. Such AC cur
-
rent, however, contains harmonics.
Inverter
The Inverter as well as normal electric machines has an input current containing har-
monics
because the Inverter
converts AC into DC. The output current of the Inverter is
comparatively
high. Therefore, the ratio of harmonics in the output current of the Invert
-
er is higher than that of any other electric machine.
Voltage
Time
Rectified
Voltage
Time
Smoothed
Voltage
Time
Current
Time
A current flows into the
capacitors. The current
is different from the
voltage in waveform.
Design Chapter
2
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