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

Vector control

4.1 Sensorless vector control (SLVC)

4.1 Sensorless vector control (SLVC)
In sensorless vector control (SLVC), the position of the flux and actual speed must be
determined via 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, the motor switches from closed-loop to
open-loop control.
The changeover between closed-loop/open-loop control is controlled by means of the time
and frequency conditions (p1755, p1756, p1758 for induction motors only). The system does
not wait for the time condition to elapse when the setpoint frequency at the ramp-function
generator input and the actual frequency are below p1755 * (1 - (p1756/100 %))
simultaneously.
Figure 4-1
In open-loop operation, the calculated actual speed value is the same as the setpoint value.
For vertical loads and acceleration processes, parameters p1610 (constant torque boost)
and p1611 (acceleration torque boost) must be modified in order to generate the static or
dynamic load torque of the drive. If, for induction motors (ASM), p1610 is set to 0%, only the
magnetizing current r0331 is injected; when the value is 100%, the rated motor current
p0305 is injected. For permanent-magnet synchronous motors (PEM), for p1610 = 0 %, a
pre-control absolute value, derived from the supplementary torque r1515, remains instead of
the magnetizing current for ASM. To ensure that the drive does not stall during acceleration,
p1611 can be increased or acceleration pre-control for the speed controller can be used.
This is also advisable to ensure that the motor is not subject to thermal overload at low
speeds.
Vector control without a speed sensor has the following features at low frequencies:
● Closed-loop operation up to approx. 1 Hz output frequency.
● Starting in closed-loop controlled operation (directly after the drive has been energized)
122
⎛ ⎞
p 1756
• −
⎜ ⎜ ⎟ ⎟
1
⎝ ⎠
100 %
Switchover conditions for SLVC
(only ASM).
p1758
Function Manual, (FH1), 10/2008, 6SL3097-2AB00-0BP5
Drive functions