Product Overview; Control; Control Principle - Danfoss VLT Decentral Drive FCD 302 Design Manual

Product Overview

2 Product Overview
Illustration 2.1 Small Unit
Illustration 2.2 Large Unit

2.1 Control

A frequency converter rectifies AC voltage from mains into
DC voltage. This DC voltage is converted into an AC
current with a variable amplitude and frequency.
The motor is supplied with variable voltage, current and
frequency, which enables infinitely variable speed control
of three-phased, standard AC motors and permanent
magnet synchronous motors.
The FCD 302 frequency converter is designed for instal-
lations of multiple smaller drives, especially on conveyor
applications, for example, in the food and beverage
industries and materials handling. In installations where
multiple motors are spread around a facility such as
bottling plants, food preparation and packaging plants and
airport baggage handling installations, there may be
dozens, perhaps hundreds, of drives, working together but
spread over a large physical area. In these cases cabling
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VLT Decentral Drive FCD 302
costs alone outweigh the cost of the individual drives and
it makes sense to get the control closer to the motors.
The frequency converter can control either the speed or
the torque on the motor shaft.
Speed control
There are two types of speed control:
Torque control
The torque control function is used in applications where
the torque on motor output shaft is controlling the
application as tension control.
Speed/torque reference
The reference to these controls can either be a single
reference or be the sum of various references including
relatively scaled references. The handling of references is
explained in detail in 2.3 Reference Handling.

2.1.1 Control Principle

The frequency converter is compatible with various motor
control principles such as U/f special motor mode, VVC
or Flux Vector motor control.
In addition, the frequency converter is operable with
Permanent Magnet Synchronous Motors (Brushless servo
motors) as well as normal squirrel cage asynchronous
motors.
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MG04H102 - VLT is a registered Danfoss trademark
•
Speed open loop control which does not require
any feedback from motor (sensorless).
•
Speed closed loop PID control, which requires a
speed feedback to an input. A properly optimised
speed closed loop control is more accurate than
a speed open loop control.
•
Closed loop in Flux mode with encoder feedback
comprises motor control based on feedback
signals from the system. It improves performance
in all four quadrants and at all motor speeds.
•
plus
Open loop in VVC mode. The function is used
in mechanical robust applications, but the
accuracy is limited. Open loop torque function
works only in one speed direction. The torque is
calculated on basic of current measurement
internal in the frequency converter. See
application example 4.5.1 Control Structure in
VVC plus Advanced Vector Control.
2 2
plus
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