S.B.C. Elettronica S.p.A. - Engineering Division
HPDxxN – High Power User’s Manual
11
2.2 Interference suppression hints
Because of the high speed voltage wavefronts in PWM, high levels of stray current may
sometimes flow through capacitive couplings and earth systems. Stray currents of this type can affect
other functional units. It is therefore prudent to calculate the presence of an amount of spurious
energy that depends on the size of the system (drives, motor lines, motor). Spurious energy generates
EM radiation that can interfere with the operation of nearby systems. Existing standards do not set
down limits for this type of radiation.
Preventive measures
Basic methods for preventing interference are:
decoupling
of drive from its surroundings, high
quality and properly sized conductors to neutralise voltages (
earthing
), and adequate
shielding
.
Shields, filters and drives must have a large contact area to achieve the maximum possible decoupling
and hence optimal noise suppression. Attention must be paid, however, to the entire installation, as
this is one of the most important precautions in assuring efficient noise suppression.
High frequency interference takes the form of radiation, especially from the motor lines. This
effect can be reduced with the use of shielding.
Another essential counter-measure for noise suppression is the use of filters.
The use of filters is aimed at reducing conducted interference on wiring and the return of
conducted interference to source (drive) through routes offering the lowest impedance. This method
provides effective protection for other systems connected to the same electrical line, also protecting
the drive from interference originating from other systems. When installing filters consider the mains
input and motor feeding output; the motor feeding output can be protected with output filters that
minimise interference levels (generally torroidal ferrite core coils bearing several windings of all three
motor wires).
2.3 Installation instructions to ensure EMC
To guarantee electromagnetic compatibility in compliance with the relevant standards the
maximum priority must be awarded to EMC requirements when designing the control cubicle. To
obtain the best results from internal filters follow the instructions in this section carefully, because
Avoid:
- routing noise emitting cables parallel to “clean” cables
- parallel cables, especially in the vicinity of the filter (ensure physical separation)
- cable loops (keep cables as short as possible and close to the common potential).
even a complex and expensive filter is ineffective unless it is
installed taking EMC aspects into consideration !
