Siemens SINAMICS G120 Operating Instructions Manual page 374

Functions
8.24 Open-loop and closed-loop control
equivalent delay time of the speed control loop. The speed controller pre-control is correctly
set (P1496 = 100 %, calibrated using P0342), if the I component of the speed controller
(r1482) does not change during a ramp-up or ramp-down in the range n > 20 % * P0310.
This means, using the pre-control, it is possible to approach a new speed setpoint without
overshoot (prerequisite: The torque limiting does not intervene and the moment of inertia
remains constant).
If the speed controller is pre-controlled, then the speed setpoint (r0062) is delayed with the
same smoothing (P1442 or P1452) as the actual value (r1445). This ensures that when
accelerating, there is no setpoint – actual value difference (r0064) at the controller input
which would have been exclusively caused by the signal propagation time.
When the speed pre-control is activated, it must be ensured that the speed setpoint is
continuously entered and without any significant noise level (avoid torque surges). An
appropriate signal can be generated by smoothing the analog signal P0753 or by activating
the rounding-off function of the ramp-function generator P1130 to P1133.
Note
The ramp-up and ramp-down times (P1120, P1121) of the ramp-function generator in the
setpoint channel should only be set so fast that when accelerating and braking, the motor
speed can follow the setpoint. This then guarantees the optimum functioning of the speed
controller pre-control.
The starting time r0345 is a measure for the overall moment of inertia of the machine and
describes that time in which the unloaded motor can accelerate from standstill to the rated
motor speed P0311 with the rated motor torque r0333.
If these secondary conditions match the particular application, then the starting time can be
used as the shortest value for the ramp-up and ramp-down times.
8-178
Operating Instructions, 11/2006, A5E00766042B AA
Control Units CU240S