Sensorless Vector Control (Slvc) - Siemens SINAMICS S120 Function Manual

5.1

Sensorless vector control (SLVC)

During operation via the "Sensorless vector control" function (SLVC), the position of the flux
and actual speed must be determined using the electric motor model. The motor model is
buffered by the incoming currents and voltages. At low frequencies (approx. 0 Hz), the motor
model cannot determine the speed with sufficient accuracy. For this reason, in this range,
the vector control can be changed over from closed-loop to open-loop control. When using
passive loads, additional limitations and constraints must be taken into consideration (see
Supplementary conditions for the operation of third-party motors).
Three-phase induction motor
The changeover between closed-loop/open-loop control is controlled by means of the time
and frequency conditions (p1755, p1756, p1758). If the setpoint frequency at the ramp-
function generator input and the actual frequency are below p1755 x (1 - (p1756/100%))
simultaneously, then the system does not wait for the time condition.
Figure 5-1
Torque setpoint setting
In open-loop operation, the calculated actual speed value is the same as the setpoint value.
For static loads (e.g. for cranes) or during acceleration, you adapt the parameters p1610
(torque setpoint static) and p1611 (additional acceleration torque) to the required maximum
torque. The drive can then generate the static or dynamic load torque that occurs. If, for
induction motors (ASM), p1610 is set to 0%, then only the magnetizing current r0331 is
impressed. If 100% is set, the rated motor current p0305 is impressed.
For permanent-magnet synchronous motors (PEM), for p1610 = 0%, a precontrol absolute
value, derived from the additional torque r1515, remains instead of the magnetizing current
of the induction motor. To prevent stalling of the drive during acceleration, the supplementary
acceleration torque p1611 can be increased or acceleration precontrol for the speed
controller can be used. This avoids thermal overloading of the motor at low speeds.
If the moment of inertia of the drive is almost constant, acceleration precontrol with p1496
offers more advantages than the supplementary acceleration torque with p1611. You can
determine the drive moment of inertia using the rotating measurement:
p1900 = 3 and p1960 = 1.
Drive functions
Function Manual, (FH1), 04/2014, 6SL3097-4AB00-0BP4
Changeover conditions for SLVC
5.1 Sensorless vector control (SLVC)
Vector control
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