Siemens SINAMICS S120 Function Manual page 124

Vector control
4.1 Sensorless vector control (SLVC)
Figure 4-3
Supplementary closed-loop control as of firmware version 2.6
With the restriction to passive loads at starting, it is now possible to maintain induction
motors in steady-state, closed-loop-controlled operation down to zero frequency (standstill)
without switching over to open-loop-controlled operation at any time.
Parameter p1750.2 must be set to 1 for this purpose.
Encoderless closed-loop control for passive loads can also be selected with p0500 = 2
(technological application = passive loads with encoderless closed-loop control down to f =
0). If p0578 = 1 (calculate technology-specific parameters) is then selected, bit 2 = 1 in
p1750 is automatically set and the function thus activated.
The function is also activated automatically if p0500 = 2 is set during quick commissioning
and quick commissioning is exited with p3900 > 0.
Closed-loop control without switchover is limited to applications with passive load:
A passive load has only a reactive effect on the drive torque of the driving motor during
starting, e.g. inert masses, brakes, pumps, fans, centrifuges, extruders.
The motor can remain at standstill without holding current for any period because only the
motor magnetizing current is injected.
It is not permissible to operate the motor steadily in generator motor at frequencies close to
zero.
124
Zero crossover for permanent-magnet synchronous motors
Function Manual, (FH1), 10/2008, 6SL3097-2AB00-0BP5
Drive functions