Modern frequency converters (see illustration below) utilise 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 [dV/dt] is the primary source of the frequency converter generated EMI.

The high rate of voltage change caused by the IGBT switching creates high frequency EMI.

AC Line

Sine wave

Illustration 5.1: Frequency Converter Functionality Diagram

Rectifier

DC Bus

Filter reactor

Filter capacitor

High Power Service Manual for Unit Sizes 6x

Inverter

IGBT