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1.6.6 Power supply harmonics
Power supply harmonics may be generated from the converter section of the inverter, affecting the power supply
equipment, power capacitors, etc. Power supply harmonics are different in generation source, frequency and
transmission path from radio frequency (RF) noise and leakage currents. Take the following measures.
z The differences between harmonics and RF noises are indicated below:
z Safeguard
Item Harmonics RF Noise
Frequency Normally 40 to 50th degrees (3kHz or less) High frequency (several 10kHz to 1GHz order)
Environment To wire paths, power impedance Across spaces, distance, laying paths
Quantitative understanding Logical computation is possible
Occurs randomly, quantitative understanding is
difficult.
Generated amount
Approximately proportional to load
capacity
According to current fluctuation rate (larger with
faster switching)
Immunity of affected device Specified in standards for each device. Differs according to maker's device specifications.
Examples of safeguard Install a reactor. Increase the distance.
The harmonic current generated from the inverter
to the power supply differs according to various
conditions such as the wiring impedance, whether
a reactor is used or not, and output frequency and
output current on the load side.
For the output frequency and output current, the
adequate method is to obtain them under rated
load at the maximum operating frequency.
CAUTION
The power factor improving capacitor and surge suppressor on the inverter output side may be
overheated or damaged by the high frequency components of the inverter output. Also, since an
excessive current flows in the inverter to activate overcurrent protection, do not provide a capacitor and
surge suppressor on the inverter output side when the motor is driven by the inverter. To improve the
power factor, insert a reactor on the inverter's primary side or in the DC circuit.
MCCB
IM
Do not insert power factor
improving capacitor.
AC reactor
Inverter
DC reactor
Motor