Application Manual CDA3000
6-29
6 Control modes
1
2
3
4
5
6
A
DE
EN
FR
6.2 Sensorless Flux
Control (SFC)
Please take note of the general information regarding the properties of
the motor control methods in the introduction to section 6 “Control
modes”.
Note: Sensorless Flux Control is only suitable for asynchronous
motors in standalone operation (not for multi-motor opera-
tion!).
Principle of Sensorless Flux Control
Sensorless Flux Control is based on activation of the motor with voltages
which are oriented to the stator flux. For the stator flux orientation a
machine model of the asynchronous motor is evaluated of which the
parameters can be determined by self-commissioning.
By transforming the currents and voltages into a system of coordinates
oriented to the stator flux, the flux and torque formation can be analyzed
in isolation from each other.
The stator flux angle ε
FS
is estimated based on the measured current
curves and the injected voltages. Consequently, the d- and q-currents and
voltages are likewise estimates. The d-components of the current and
voltage point in the direction of the stator flux and thus contribute to
formation of the field (flux-forming). The 90˚ offset q-components of the
current and voltage run transverse to the stator flux and form the torque.
This correlation is illustrated in Figure 6.15.
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