Efficient Networks Siemens Sinamics S120 - Manual (Page 236)

Function modules
7.7 Extended torque control (kT estimator, Servo)
Drive Functions
236
Function Manual, (FH1), 07/2007 Edition, 6SL3097-2AB00-0BP4
Parameter r0108.1 indicates whether it has been activated.
Description of the k
T
estimator
The adaptation of the torque constants for synchronous motors is used to improve the
absolute torque accuracy for the control (closed-loop) of synchronous motors. The
magnetization of the permanent magnets varies as a result of production tolerances and
temperature fluctuations and saturation effects. This function "k
T
estimator" adapts the
torque constant k
T
[Nm/A] in the control to the instantaneous magnetization. It only makes
sense to use the k
T
estimator in conjunction with the friction characteristic as the k
T
estimator
can only correct the inner motor torque. The frictional losses must be compensated from the
friction characteristic using a supplementary torque.
The k
T
estimator requires the most accurate values for the motor parameters as possible in
order to achieve a high torque accuracy. Before using the k
T
estimator, it is therefore
necessary to carry-out a motor identification routine (p1909, p1910) with the k
T
estimator
activated; this determines the values for the stator resistance (p0350), leakage inductance
(p0356) and voltage emulation errors (p1952, p1953). The cable resistance must be entered
in p0352 before motor identification.
The motor should be at room temperature when the identification routine is carried out.
Compensation of the voltage emulation error must be activated (p1780.8 = 1). The motor
temperature (p0600) should be recorded via a KTY sensor (p0601 = 2 or 3).
The estimator requires the motor temperature in order to track/correct the temperature-
dependent quantities. If a motor temperature sensor is not connected, then the accuracy is
significantly restricted.
The k
T
estimator is only activated above a specific speed (p1752). The terminal voltage of
the drive converter always has small errors, caused by voltage drives across the power
semiconductors etc. The lower the speed and therefore the output voltage, the greater the
negative influence on the estimation as a result of low voltage errors. This is the reason that
the estimation is de-activated below a specific speed. The estimated value is smoothed
using time constant p1795. The correction value for the torque constant is displayed in
r1797. By identifying the torque constant k
T
using the rotating motor identification routine, the
torque accuracy can be improved also below the speed threshold (p1752).
The k
T
estimator is activated using p1780.3 and the voltage compensation using p1780.8.
Function diagrams (see SINAMICS S List Manual)
● 7008 kT estimator
Overview of key parameters (see SINAMICS S List Manual)
● r0108.1 Function module - extended torque control active
● p1780.3 Selects motor model PEM k
T
adaptation
● p1780.8 Compensation of the voltage emulation error in the drive converter
Motor/drive converter identification
● p0352 Cable resistance
● p1909 Motor data identification control word
● p1910 Activates motor data identification routine, stationary (standstill)