21
P50051 = 28. These compensations offload the speed controller and permit a higher speed
control dynamic response.
Selection of compensation via p50223 = 1, Sheet 6815
Torque calculation:
Sheet 6820. Depending on the setting for p50170, the output of the speed controller
indicates the torque setpoint or the current setpoint. The motor torque is determined using
flux Phi of the motor. For theory, see below
Setting: p50170 = 0, the speed controller output is the current setpoint that can be passed on
to the current controller without any further calculation (except limitations).
P50170 = 1, the speed controller output indicates the torque setpoint, the current setpoint for
the current controller is determined by the next calculation M/ . One advantage here is that
the controlled system gain of the speed control loop is adapted suitably automatically within
the field weakening range of the motor, producing a stable speed control response.
Torque setpoint before limitation: r52145, after limitation: r52141.
The precision of the torque control dependent on the device is approx. 3%. (influence of
actual current sensing, armature and field, taken into account and field characteristic curve
recording performed, if there is field weakening). The influence of the motor is low for a fully
compensated motor, but motor-related for a non-compensated motor.
Note
: If the motor is only operated in the armature setting range (no field weakening), flux
is always 100% and setting p50170 = 1 has no effect.
If p50170 = 1, p50169 = 0 must be set.
Current setpoint integrator / Reduced gearbox stressing
Sheet 6845, p50157 = 1, current setpoint integrator: The ramp-function generator for the
current setpoint is effective for every current setpoint change of r52120, recommended
setting.
P50157 = 0, reduced gearbox stressing: The ramp-function generator time is only effective
for a change of torque direction.
p50158 = Ramp-up time in seconds
On old motors, set p50157 = 1 and p50158 = approx. 0.04 s, required for good commutation
of the current in the old motor.
Actual value of current
The armature current is sensed on the AC input side by one current transformer in each of
the U and W phases. The current transformer load for each current transformer is on the
power interface module and is 10 ohm. The load voltage is evaluated on the power interface
board. The rated DC current of the SINAMICS DCM is adapted via the transformation ratio of
the current transformer and electronically on the power interface board.
The DC actual value is formed from the two load voltages of the current transformers on the
power interface board with electronic rectification (A/D converter). 100 % are the value of
r05072[1] after normalization via p50076[0] and/or p50067.
The precision of the sensed armature current is 1% of the nominial value.
Note:
Both of the current transformers must always be loaded with a load resistor, otherwise
they will be damaged by internal overvoltage on current flow.
Current control loop
Sheet 6855
The current control loop adjusts any deviation of the current setpoint: r52118 (100%
corresponds to the value of r50072[1] and of the current actual value: r52019 (100%
corresponds to the value of p50100) to zero. In the current control loop the current controller
acts as the PI controller. Current controller precontrol is active at the same time. The output
of the current controller and the precontrol are added and the sum of the two quantities forms
the firing angle.
Current controller: The current controller is a PI controller; its parameters for optimization are
the Kp (p50155) and the reset time Tn (p50256). For optimization, see below.
Depending on the parameter settings can also be run as a P or I controller.
p50154 = 1, p50164 = 1; PI controller, factory setting
p50154 = 0, p50164 = 1; P controller
p50154 = 1, p50164 = 0; I controller
