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H
Countermeasures against Harmonics
With the continuing development of electronics, the generation of harmonics from industrial machines
has been causing problems recently. Refer to the following for the definition of harmonics (i.e., harmonic
currents with voltages) and countermeasures against the generation of harmonics from the Inverter.
D
Harmonics (Harmonic Currents with Voltages)
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Definition
Harmonics consist of electric power produced from AC power and alternating at frequencies that are
integral multiples of the frequency of the AC power.
The following are the harmonic frequencies of a 60- or 50-Hz commercial power supply.
Second harmonic:
120 (100) Hz
Third harmonic:
180 (150) Hz
Basic frequency
(60 Hz)
Second harmonic (120 Hz)
Third harmonic (180 Hz)
•
Problems Caused by Harmonics Generation
The waveform of the commercial power supply will be distorted if the commercial power supply con-
tains excessive harmonics.
Machines with such a commercial power supply will malfunction or generate excessive heat.
Third harmonic (180 Hz)
Basic frequency (60 Hz)
Distorted current
waveform
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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 difference in current flow between AC
and DC.
•
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 current, however, contains har-
monics.
Installation
Chapter 2
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