3 Internal Frequency Converter Operation
3.1 General
This section is intended to provide an operational overview
of the frequency converter’s main assemblies and circuitry.
With this information, a repair technician should have a
better understanding of the frequency converter's
operation and aid in the troubleshooting process.
3.2 Description of Operation
A frequency converter is an electronic controller that
supplies a regulated amount of AC power to a three phase
induction motor in order to control the speed of the
motor. By supplying variable frequency and voltage to the
motor, the frequency converter controls the motor speed,
or maintains a constant speed as the load on the motor
changes. The frequency converter can also stop and start a
motor without the mechanical stress associated with a line
start.
In its basic form, the frequency converter can be divided
into four main sections: rectifier, intermediate circuit (DC
bus), inverter, and control (see Illustrations 3.1 and 3.2).
Illustration 3.1 F-frame Internal Processing
L11
L21
L31
L12
L22
L32
T1
T2
T3
130BX422.10
Filter capacitor
Filter reactor
Filter capacitor
Filter reactor
Rectifier
DC Bus
Inverter
AC Line
AC Line
Sine wave
IGBT
Motor
PWM waveform
Illustration 3.2 12-pulse Internal Processing
The main frequency converter components are grouped
into three sections consisting of control logic, logic to
power interface, and power. These are covered in greater
detail in Sequence of Operation which describes power
and control signals within the frequency converter.
3.2.1 Logic Section
The control card contains most of the logic section (see
Illustration below). The primary logic element of the
control card is a microprocessor, which supervises and
controls all functions of frequency converter operation. In
addition, separate PROMs contain the parameters to
provide the user with programmable options. These
parameters are programmed to enable the frequency
converter to meet specific application requirements. This
data is then stored in an EEPROM which provides security
during power-down and also allows the flexibility to
change the operational characteristics of the frequency
converter.
A custom integrated circuit generates a pulse width
modulation (PWM) waveform which is then sent to the
interface circuitry located on the power card.
Internal Frequency Converte...
High Power Service Manual for Modular F Frame Drives
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