Output filters - sine-wave filters for frequency converters

The output voltage of the frequency converter is a
series of trapezoidal pulses with a variable width (pulse-width modulation),
characterized by a pulse rise-time tr.

If an insulated-gate bipolar transistor (IGBT) is switched on inside the converter, the voltage applied to
the motor increases proportionally to the dU/dt ratio
in accordance with the following functions:
• Motor cable (type, length, width, with/without
protection, inductance, and capacitance).
• the impedance of the motor in the high frequency range
Due to the imbalance between the impedance
of the cable and the impedance of the motor,
wave reflection occurs which causes the voltage
of the motor terminals to overshoot (see Figure 3.1). The
motor impedance decreases as
the motor size increases, resulting in less of an imbalance
with the impedance of the cable. The lower reflection coefficient (Γ)
reduces the wave reflection, along with the overshooting voltage.
See Table 3.1 for common values.
For parallel cables, the impedance of the cable
is reduced, resulting in a higher reflection coefficient and
more powerful overshooting. For more information, please
see IEC 61800-8.