Omron RX Series User Manual page 90

2 Design
Harmonic Current Measures and DC/AC Reactor Wiring (+1, P/2)
In recent years, there is an increasing concern about harmonic currents generated from industrial
machinery.
The following provides an overview of harmonics and measures against harmonics implemented in this
inverter.
 Harmonics
The voltage or current whose frequency is an
integral multiple of certain standard frequency
(base frequency) is called a harmonic.
If a commercial power supply frequency of 60 Hz
(50 Hz) is the reference frequency, the harmonics
of that signal is:
x2 = 120 Hz (100 Hz),
x3 = 180 Hz (150 Hz), and so on.
 Reason why harmonics cause
problems
As the number of harmonics increases, the
waveform of the commercial supply has more
distortion. This distortion causes the malfunction
of the connected equipment or leads to abnormal
heat generation.
 Causes of harmonics
• General electrical equipment internally
converts AC input power (commercial power)
into DC power. At this time, harmonic currents
occur because of the difference in the current
flow direction between AC power and DC
power.
• In an AC-to-DC power conversion, the rectifier
converts the input power into a unidirectional
voltage, which is then smoothened by the
capacitor. As a result, the current charged into
the capacitor has a waveform that contains
harmonic components.
• This inverter also performs an AC-to-DC
conversion as with other electrical equipment,
which allows current with harmonic
components to flow. In particular, the inverter
has more current than other equipment, so the
number of harmonic components in current is
larger.
2 - 34
Base frequency
(60 Hz)
Base frequency (60 Hz)
Distorted waveform
Voltage
Voltage
Voltage
Current
Current flows only during the charging of a capacitor.
The waveforms of current differs from voltage.
High-function General-purpose Inverter 3G3RX-V1 User's Manual (I578-E1)
2nd harmonics (120 Hz)
3rd harmonics (180 Hz)
3rd harmonics (180 Hz)
Time
Conversion with a rectifie
Time
Smoothing with a capacitor
Time
Time