Efficient Networks S120 Description of the kT estimator, Motor/drive converter identification

Function modules

7.7 Extended torque control (kT estimator, Servo)

Parameter r0108.1 indicates whether it has been activated.

Description of the kT 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 "kT estimator" adapts the torque constant kT [Nm/A] in the control to the instantaneous magnetization. It only makes sense to use the kT estimator in conjunction with the friction characteristic as the kT estimator can only correct the inner motor torque. The frictional losses must be compensated from the friction characteristic using a supplementary torque.

The kT estimator requires the most accurate values for the motor parameters as possible in order to achieve a high torque accuracy. Before using the kT estimator, it is therefore necessary to carry-out a motor identification routine (p1909, p1910) with the kT 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 kT 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 kT using the rotating motor identification routine, the torque accuracy can be improved also below the speed threshold (p1752).

The kT 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 kT 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)

236	Drive Functions
	Function Manual, (FH1), 07/2007 Edition, 6SL3097-2AB00-0BP4