Danfoss VLT AutomationDrive FC 300 Series - Controls; Control Principle

3.2 Controls
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 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
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 1-00 Configuration Mode, either in VVC
plus
[4]
Torque open loop or Flux control closed loop with [2] motor
speed feedback. Torque setting is done by setting an
analog, digital or bus controlled reference. The max speed
limit factor is set in 4-21 Speed Limit Factor Source. 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
plus
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.
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
VLT
®
AutomationDrive FC 300 Design Guide, 0.25-75 kW
16 MG33BE02 - VLT
®
is a registered Danfoss trademark
3
3
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