Siemens SINAMICS S120 Function Manual page 109

The switchover is governed via time and frequency conditions (p1755, p1756, and
p1758). The system does not wait for the time condition to elapse when the set-
point frequency at the ramp-function generator input and the actual frequency are
below p1755 * (1 -- p1756) simultaneously.
p1755 [1/min]
p1755 [1/min]
* (1 -- p1756)
Open control loop
Closed control loop
Fig. 3-23
In open-loop operation, the calculated actual speed value is the same as the set-
point value. For vertical loads and acceleration, 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 p1610 is set to 0%, only
the magnetizing current (r0331) is injected; when the value is 100%, the rated mo-
tor current (p0305) is injected. To ensure that the drive does not stall during accel-
eration, 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 ther-
mal overload at low speeds.
Vector control without a speed sensor has the following characteristics at low
frequencies:
S Closed-loop operation up to approx. 1 Hz output frequency
S Start-up in closed-loop operation (directly after drive is energized)
Note
In this case, the speed setpoint upstream of the ramp-function generator must be
greater than (p1755).
© Siemens AG, 2005. All rights reserved
SINAMICS S120 Function Manual, 06/05 Edition
f_act
⎟ ⎟
Switchover conditions for SLVC
p1758
Operating Modes
Vector control
t
t
3-109