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.
130BX137.
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AC Line
Rectifier
DC Bus
Inverter
Motor
Filter reactor
IGBT
Filter capacitor
PWM waveform
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
130BX138.
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Motor Cable
AC Line
Ground
Potential 1
Potential 2
Potential 3
VFD
Motor
Stray capacitance
Stray capacitance
Figure 5.2 Ground Currents
Adjustable Frequency Drive ...
Service Manual
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Danfoss A/S © Rev. 2014-02-10 All rights reserved.
MG94A222
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