3.2.1 Control Principle
An adjustable frequency drive rectifies AC voltage from line into DC voltage, after which 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.
3.2.2 AutomationDrive FC 300 Controls
The adjustable frequency drive is capable of controlling either the speed or the torque on the motor shaft. Setting par. 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 the motor (sensorless).
•
Speed closed-loop PID control requires a speed feedback to an input. Properly optimized speed closed-loop control will have higher accuracy
than speed open-loop control.
Selects which input to use as speed PID feedback in par. 7-00
Speed PID Feedback Source
.
Torque control (AutomationDrive 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 adjustable frequency drive. See
Application Example Torque Open-loop
Speed / torque reference:
The reference to these controls can either be a single reference or the sum of various references including relatively scaled references. The handling of
references is explained in detail later in this section.
3 Introduction to AutomationDrive FC 300
FC 300 Design Guide
3-4
MG.33.BC.22 - VLT
®
is a registered Danfoss trademark
3