Sources Of Emi - Danfoss VLT HVAC Drive FC100 Service Manual

Frequency Converter and Mot...

5.3.2 Sources of EMI

Modern Frequency converters (see illustration below) utilise 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, and variable voltage PWM waveform. This high rate of voltage change
[dV/dt] is the primary source of the frequency converters generated EMI.
The high rate of voltage change caused by the IGBT switching creates high frequency EMI.
5 5
AC Line
Sine wave
Illustration 5.1 F-frame Functionality Diagram
Illustration 5.2 12-pulse Functionality Diagram
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High Power Service Manual for Modular F Frame Drives
Rectifier DC Bus
Filter reactor
Filter capacitor
Recti er
AC Line
L11
L21
L31
Sine wave
AC Line
L12
L22
L32
MG90K202 - VLT
Inverter
IGBT
DC Bus Inverter
Filter reactor
IGBT
Filter capacitor
Filter reactor
Filter capacitor
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PWM waveform
Motor
T1
T2
T3
PWM waveform
Motor