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Appendix 2 EMI Prevention
Appendix 2 EMI Prevention
Appendix Table 1: Inverter System EMI Prevention
The electromagnetic environment is very complicated in industrial occasions.
Besides, the inverter's working principle also decides that EMI exists in the
inverter itself. So it is very important to solve EMC problems effectively to
ensure reliable running of the system in such a comprehensive condition. In this
chapter, we give a research on EMC and provide corresponding solutions to EMC,
i n h o p e o f b e i n g h e l p f u l t o y o u t o s o l v e p r a c t i c a l p r o b l e m s .
EMI Types and propagation mode
Type
Propagation mode
Conducted interference A
Common-base impedance
coupling
Common source impedance
coupling
adiated interference
Near field coupling
Far field coupling
Inductive
interference C:
Electric coupling
Magnetic field induction
2) Inverter System EMC Solutions
Power supply input cable
The distortion of power grid waveform caused by superimposed higher harmonic
current arisen out of nonlinear rectifier circuit to source impedance may lead to
interference over other electrical equipment under the same power grid. This kind of
interference is named type A interference.
The power current and higher harmonic current brings in alternating
electromagnetic field around the circuit cable, which results in electric field
coupling and magnetic flux inductive coupling to the nearer parallel cable such as
the communication cable, small signal transmission cable and etc. This kind of
interference is named type C
or C interference.
Due to antenna effect of the cable's shielding layer, interference may be produced
over external wireless installation. This kind of interference is named type B
interference.
Communication
equipment
Communication cable
Small signal transfer cable
Other electronic
equipment Wireless
installation
Inverter
Industrial meter
Propagation Diagram of Input Cable's Interference over External Equipment
This type of interference can be suppressed by installing an EMI power
supply filter or isolation transformer in the power supply input side.
This type of interference can be suppressed through well ordered wiring or
shielding. For example, the signal cable may adopt shielded wire and the
shielding layer shall be firmly grounded to reduce magnetic flux inductive
coupling and electric field coupling. The signal cable should be at least 100mm
away from the power cable. If the signal wire and the power cable intersect,
please intersect orthogonally. Generally speaking, it is not advisory to use an
overlong signal wire. If the operation instruction is far from the inverter, then it
is recommended to use an intermediate relay to have a control over it, as shown
in the figure below.
Solutions
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