6.8.2.2 Start-up of a sensorless-controlled asynchronous motor
in I/f mode
P No.
Index Name
Unit Description
792
EN_CH4_Kalman_SigInj
Sensorless control: Test signal generator
0
Signal
7
FullSignalRange
rpm SC test signal: Linear transition range up until
which the test signal is reduced to 0
8
IncreasingSignalRange
rpm SC test signal: Linear transition range up until
which the test signal is reduced to 0
9
d current offset
A
SC test signal: d current offset of sinusoidal
signal
Table 6.33: Parameters for start-up of a sensorless-controlled asynchronous motor
in I/f mode
An asynchronous motor is not suitable for sensorless positioning due to its design
because the rotor does not have a fixed magnetic pole. Moreover, asynchronous
motors controlled without sensors tend to have unstable behaviour at low speeds
and low torques in generator mode.
First attempt to use the SFC controller in the proximity of the standstill. (P 792.0
signal = 0). This allows gentle operation and an optimal torque utilization. Set the
standstill behaviour with the error voltage model P 1973.1 U_err; generally, a setting
of 50% of the original setting yields good results.
It is possible that a flux boost may improve the results at low speeds when a large
load is set in motion from a standstill. Set P 792[0] Signal =1, P 792[1] to 50 . . .200
rpm, P 792[2] to 200 . . . 500 rpm and P 792[7] to the d current required for starting. If
the motor tends to tip, then attempt to limit the permissible slip using P 1959[1] K_ov.
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If the stability and the torque in the proximity of standstill are inadequate, use the
current/frequency mode (I/f). Set P 792[0] Switch = 2. Set the speed limits P 792[7]
and P 792 [8] lower than for the use of flux boost. The d current P 792 [9] must be
adequate to set the maximum possible load in motion when starting.
Bear in mind that a certain control gain K_isd is required for the momentary current;
for this purpose, observe the scope signals of Isd and Isdref during acceleration.
With P 792 [0] signal = 3, the drive also works in I/f control mode at low speeds.
When the "full-signal range" speed is attained, then a switch to SFC control takes
place at once.
Whether a setting of "2" or "3" is the better choice depends on the application.
