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 con-
verts the input power into a unidirectional voltage,
which is then smoothened by the capacitor. As a re-
sult, 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 cur-
rent 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.
Voltage
Time
Conversion with a rectifier
Smoothing with a capacitor
Current flows only during the charging of a capacitor.
The waveforms of current differs from those of voltage.
Time
Time
Time
Voltage
Voltage
Voltage
DC/AC reactor
To suppress harmonic currents, use the DC (direct current) and AC (alternating current) reactors.
The DC/AC reactor functions to suppress a steep change in the current.
The DC reactor has a higher harmonics suppression ability
, so even higher suppression ability can
be expected when used in conjunction with the AC reactor.
Suppressing harmonic currents also leads to the improvement in the power factor on the input or
output side of the inverter
.
Before wiring
The DC reactor is connected to the DC power supply located inside the inverter.
Before wiring, be sure to turn OFF the power supply and make sure that the charge indicator is not
lit.
Do not touch the interior of the inverter during inverter operation. Doing so may result in electric
shock or burn injury.
By factory default, a short-circuit bar is connected between the terminals P1 and P(+). Before con-
necting the DC reactor, remove this short-circuit bar.
Note that the length of the DC reactor connection cable must be 10 m or shorter.
Remove the short-circuit bar only if you connect the DC reactor for use.
If you remove the short-circuit bar with the DC reactor unconnected, the inverter cannot operate
because no power is supplied to its main circuit.
2 Design
2-46
M1 Series Standard Type User's Manual (I669)
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