Appendix A. EMC Standard Installation GuideVFD-ED
A-5-2 Harmonic Interference
The AC motor drive’s input current is non-linear, the input rectifier generates harmonics. Harmonics
must be limited to within a certain range to avoid impact the mains power and to avoid current
distortion to ensure surrounding devices are not influenced. An AC Motor Drive with built-in DC reactor
suppresses harmonic currents (Total Harmonic Current Distortion THID) effectively and therefore
reduces the harmonic voltage peaks (Total Harmonic Voltage Distortion).
Harmonic Current at the Power Supply Side
(A) Fundamental Sine Wave
(6 0Hz)
(B) Ha rmo nic
(1 80H z)
3
rd
(C) Harmonically
Distorted Wave
(B) Ha rmon ic
(300Hz)
5
th
(C) Harmonically
Distorted Wave
(A) Fundamental Sine Wave
(6 0Hz)
Suppression of Harmonic Currents
Reactor
When a large portion of lower order harmonic currents (5
th
, 7
th
, 11
th ,
etc.) occur at the power input,
surrounding devices will be disturbed and the power factor will be low as a result of reactive power.
Installing a reactor at the AC Motor Drive’s input effectively suppresses lower order harmonic currents.
Line
Chokes
Bus
Choke
Inverter
Motor
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