2-1
12AN OVERVIEW OF THE CONVERTER
How it Works
Note: Refer to Chapter 9: “Control Loops” for a more detailed explanation.
In very simple terms, the Converter controls the dc motor with the use of Control Loops - an
inner Current Loop and an outer Speed Loop. These control loops can be seen in the Application
Block Diagram. The block diagram shows all the Converter’s software connections.
Using the Man-Machine Interface (MMI), you can select the control loops to be used by the
Converter to provide either:
• Current Control
• Speed Control (default)
It is usual to supply a Current or Speed Feedback signal to the appropriate loop for more
effective control of the Converter. Current Feedback sensors are built-in, whereas Speed
Feedback is provided directly from the armature sensing circuit (default), or by tachogenerator,
encoder or Microtach connection to the relevant option board.
When in Speed Control,
you can modify the
performance of the
Converter further by
controlling the motor
field, i.e. Field Control.
By weakening the field
current, you can obtain
an increase in motor
speed beyond that
normally achievable for
the rated Armature
Voltage of the dc motor.
The Converter is controlled remotely using digital/analog inputs and outputs. It cannot be
directly stopped or started using the MMI.
A remote 5721 Operator Station can also be connected. This allows you to read and write to
many of the drive’s parameters from outside the cubicle if required.
By plugging in a COMMS Option Board, the Converter can be linked into a network and
controlled by a PLC/SCADA or other intelligent device.
Field Current 5.7A
Voltage 200V
Speed
speed increase
due to field
weakening
armature voltage
remains constant
field current
reduced
base
speed
Armature
REMOTE START/STOP
REMOTE
SPEED CONTROL
SPEED SETPOINT
REMOTE START/STOP
REMOTE
SPEED CONTROL
SPEED SETPOINT
5721
Operator
Station
Analog/Digital Inputs and Outputs
Analog/Digital Inputs and Outputs
5721 Operator Station and
MMI
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