3.2 Controls
The adjustable frequency drive 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:
•
Open-loop does not require any feedback from motor (sensorless).
•
Closed-loop PID requires a speed feedback to an input. A properly optimized speed closed-loop control has higher
accuracy than a speed open-loop control. The speed 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 the motor output shaft is controlling the
application as tension control. Torque control is selected in
1-00 Configuration Mode
, either in
[4] VVC
plus
open-loop
or
[2] Flux
control closed-loop with 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 since the correct motor data is essential 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 mechanically robust applications, but its accuracy is limited.
Open-loop torque function works only in one speed direction. The torque is calculated on the basis of current
measurement within the adjustable frequency drive. See.
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. For more information on reference handling, see
chapter 3.3 Reference Handling
Product Introduction
Design Guide
MG34S222
Danfoss A/S © Rev. 2014-02-10 All rights reserved.
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