Control Principle - Danfoss VLT Decentral Drive FCD 302 Design Manual

Product Overview and Functi...
Speed control
Two types of speed control:
•
Speed open-loop control, which does not require
any feedback from the motor (sensorless).
•
Speed closed-loop PID control, which requires a
speed feedback to an input. A properly optimized
speed closed-loop control is more accurate than a
speed open-loop control.
Torque control
The torque control function is used in applications where
the torque on motor output shaft controls the application
as tension control.
•
Closed loop in flux mode with encoder feedback
comprises motor control based on feedback
signals from the system. It improves performance
in all 4 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 only

2.2.1 Control Principle

The frequency converter is compatible with various motor control principles such as U/f special motor mode, VVC
vector motor control.
In addition, the frequency converter is operable with permanent magnet synchronous motors (brushless servo motors) and
normal squirrel lift cabin asynchronous motors.
The short circuit behavior depends on the 3 current transducers in the motor phases and the desaturation protection with
feedback from the brake.
L1 91
L2 92
L3 93
Illustration 2.5 Control Principle
MG04H302
Design Guide
R inr
P 14-50
Danfoss A/S © 05/2018 All rights reserved.
in 1 speed direction. The torque is calculated on
basis of current measurement internal in the
frequency converter. See application example
chapter 2.3.1 Control Structure in VVC
Vector Control.
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. The handling of references is
explained in detail in chapter 2.6 Handling of Reference.
Inrush
2
+ Advanced
+
, or flux
Brake
R+
82
Resistor
R-
81
U 96
V 97
M
W 98
15
2