Siemens Sinamics S120 Function Manual page 145

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 * (1 - (p1756/100 %))
simultaneously, then the system does not wait for the time condition.
Figure 4-1
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 accelerating torque) to the required maximum
torque. The drive can then generate the static or dynamic load torque generate 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 pre-control 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
accelerating torque p1611 can be increased or acceleration pre-control 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 accelerating torque with p1611. You can
determine the drive moment of inertia using the rotating measurement:
p1900 = 3 and p1960 = 1.
Encoderless vector control has the following characteristics at low frequencies:
● Closed-loop controlled operation for passive loads up to approx. 0 Hz output frequency
● Start an induction motor in the closed-loop controlled mode (after the motor has been
Drive functions
Function Manual, (FH1), 01/2012, 6SL3097-4AB00-0BP2
⏐f_act⏐
p1755 [1/min]
p1755 [1/min]
⎛ ⎞
p 1756
• −
⎜ ⎜ ⎟ ⎟
1
⎝ 100 % ⎠
Changeover conditions for SLVC
(p0500 = 2), for p1750.2 = 1 and p1750.3 = 1).
completely excited), if the speed setpoint before the ramp-function generator is greater
than p1755.
4.1 Sensorless vector control (SLVC)
p 1758
Vector control
t
t
143