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3.2.1 Control Principle
A frequency converter rectifies AC voltage from mains into
DC voltage, after which this DC voltage is converted into a
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.
3.2.2 FC 300 Controls
The frequency converter is capable of controlling either
the speed or the torque on the motor shaft. Setting
1-00 Configuration Mode
determines the type of control.
Speed control:
There are two types of speed control:
•
Speed open loop control which does not require
any feedback from motor (sensorless).
•
Speed closed loop PID control requires a speed
feedback to an input. A properly optimised speed
closed loop control will have higher accuracy
than a speed open loop control.
Selects which input to use as speed PID feedback in
7-00 Speed PID Feedback Source
.
Torque control (FC 302 only):
The torque control function is used in applications where
the torque on motor output shaft is controlling the
application as tension control. Torque control can be
selected in par. 1-00, either in VVC+ open loop [4] or Flux
control closed loop with motor speed feedback [2]. Torque
setting is done by setting an analog, digital or bus
controlled reference. The max speed limit factor is set in
par. 4-21. When running torque control it is recommended
to make a full AMA procedure as the correct motor data
are of high importance for optimal performance.
•
Closed loop in Flux mode with encoder feedback
offers superior performance in all four quadrants
and at all motor speeds.
•
Open loop in VVC+ mode. The function is used in
mechanical robust applications, but the accuracy
is limited. Open loop torque function works
basically only in one speed direction. The torque
is calculated on basic of current measurement
internal in the frequency converter. See
Application Example Torque open Loop
Speed / torque reference:
The reference to these controls can either be a single
refrence or be the sum of various references including
relatively scaled references. The handling of references is
explained in detail later in this section.
Introduction to FC 300
FC 300 Design Guide
MG.33.BD.02 - VLT
®
is a registered Danfoss trademark
17
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