Power supply harmonics
Power supply harmonics
The inverter may generate power supply harmonics from its converter circuit to affect the power generator, power factor
correction capacitor etc. Power supply harmonics are different from noise and leakage currents in source, frequency band and
transmission path. Take the following countermeasure suppression techniques.
• Differences between harmonics and noises
Affected equipment immunity
The harmonic current generated from the inverter to the input side 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, we understand that this should be calculated in the conditions under the rated
load at the maximum operating frequency.
• The power factor improving capacitor and surge suppressor on the inverter output side may be overheated or damaged by the
harmonic 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.
For power factor improvement, install a reactor on the inverter input side or in the DC circuit.
Harmonic suppression guidelines in Japan
Inverters have a converter section (rectifier circuit) and generate a harmonic current.
Harmonic currents flow from the inverter to a power receiving point via a power transformer. The Harmonic Suppression
Guidelines was established to protect other consumers from these outgoing harmonic currents.
Normally 40th to 50th degrees or less (3
kHz or less).
To-electric channel, power impedance.
Theoretical calculation possible.
Nearly proportional to the load capacity.
Specified by standards per equipment.
Provide a reactor.
Do not install power
factor improving capacitor.
High frequency (several 10 kHz to 1 GHz order).
To-space, distance, wiring path.
Random occurrence, quantitative grasping difficult.
Changes with the current variation ratio. (Gets
larger as switching speed increases.)
Different depending on maker's equipment
3. PRECAUTIONS FOR USE OF THE INVERTER
3.2 Power supply harmonics