Sources Of Emi; Emi Propagation - Danfoss VLT FC 100 Service Manual

Adjustable Frequency Drive ...

5.2.5 Sources of EMI

Adjustable frequency drives utilize insulated-gate bipolar transistors (IGBTs) to provide an efficient and cost effective means
to create the pulse width modulated (PWM) output waveform necessary for accurate motor control. These devices rapidly
switch the fixed DC bus voltage creating a variable frequency, variable voltage PWM waveform. This high rate of voltage
change [dU/dt] is the primary source of the adjustable frequency drive generated EMI.
The high rate of voltage change caused by the IGBT switching creates high frequency EMI.
5 5
AC Line
Sine wave
Figure 5.1 Adjustable Frequency Drive Functionality Diagram

5.2.6 EMI Propagation

Adjustable frequency drive generated EMI is both conducted to the line power and radiated to nearby conductors. See
Figure 5.2.
AC Line
Ground
Figure 5.2 Ground Currents
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Service Manual
Rectifier DC Bus
Filter reactor
Filter capacitor
VFD
Potential 1
Danfoss A/S © Rev. 2014-02-10 All rights reserved.
Inverter
IGBT
Motor
Motor Cable
Stray capacitance
Potential 2
Motor
PWM waveform
Stray capacitance
Potential 3
MG94A222