Efficient Networks Siemens Sinamics S120 - Manual (Page 119)

Vector control
4.3 Speed controller
Drive Functions
Function Manual, (FH1), 07/2007 Edition, 6SL3097-2AB00-0BP4
119
● Compared with speed control without an encoder, the dynamic response of drives with an
encoder is significantly better because the speed is measured directly and integrated in
the model created for the current components.
● Higher speed accuracy
Motor model change
A model change takes place between the current model and the observer model within the
speed range p1752*(100%-p1756) and p1752. In the current model range (i.e at lower
speeds), torque accuracy depends on whether thermal tracking of the rotor resistance is
carried out correctly. In the observer model range and at speeds of less than approx. 20% of
the rated speed, torque accuracy depends primarily on whether thermal tracking of the stator
resistance is carried out correctly. If the resistance of the supply cable is greater than 20% to
30% of the total resistance, this should be entered in p0352 before motor data identification
is carried out (p1900/p1910).
To deactivate thermal adaptation, set p0620 = 0. This may be necessary if adaptation cannot
function accurately enough due to the following general conditions: for example, if a KTY
sensor is not used for recording the temperature and the ambient temperatures fluctuate
significantly or the overtemperatures of the motor (p0626 ... p0628) deviate significantly from
the default settings due to the design of the motor.
4.3 Speed controller
Both closed-loop control procedures with and without an encoder (VC, SLVC) have the same
speed controller structure, which contains the following components:
● PI controller
● Speed controller pre-control
● Droop
The total of the output variables result in the torque setpoint, which is reduced to the
permissible magnitude by means of the torque setpoint limitation.
Speed controller
The speed controller receives its setpoint (r0062) from the setpoint channel and its actual
value (r0063) either directly from the speed sensor (control with sensor (VC)) or indirectly via
the motor model (control without sensor (SLVC)). The system deviation is increased by the
PI controller and, in conjunction with the pre-control, results in the torque setpoint.
When the load torque increases, the speed setpoint is reduced proportionately when droop
is active, which means that the single drive within a group (two or more mechanically
connected motors) is relieved when the torque becomes too great.