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. 21
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