25
P50081 = 1, p50117 = 1, p50253 = 0.
In this case, the precontrol of the EMF control loop is disabled and the field weakening
control is only performed by the EMF controller, field characteristic curve recording is then
not necessary.
If p50081 = 0 no field weakening control is performed and the field current is input as a
constant quantity, the EMF control loop is not active.
Field current setpoint limitation
After the output of the EMF control loop, a field current setpoint limitation takes effect.
The upper limit value is determined by r50073[1], the rated field current for the SINAMICS
DCM. Additionally, multiplying influence on the limit is possible by entering the required
connector number in p50613.
The field current setpoint lower limit is determined by p50103 and a connector variable with a
multiplying effect for the connector selected in p50614.
Actual value for field current
The actual field current value is sensed by means of shunt resistors on the field module. The
shunt resistance complement is dependent on the device data. The voltage drop of the shunt
resistors is converted by a A/D converter on the field supply board.
100 % of r50073[1] corresponds to the current field nominal current for a 100% actual field
current value for the field current control. The rated device field current r50073[1] results in
the currently applicable rated device current, field after adjustment with p50076[1]
(1 to 100%) for the field current control.
The precision of the actual value sensed for the field current is 1% of the nominal value.
Field current control loop
Sheet 6910, field current controller:
P50254 = 1, p50264 = 1 The controller acts as the PI controller, factory setting,
recommended setting
P50254 = 0, p50264 = 1, The controller acts as the P controller
P50254 = 1, p50264 = 0, The controller acts as the I controller
Optimization variables for the controller: Gain Kp (p50255) and reset time Tn (p50256).
the PI field current controller adjusts the field current to a setpoint/actual value difference of
zero and provides the firing angle for the field current gating unit as the output.
A precontrol is active at the same time and has a different characteristic curve than the
armature current control loop because it includes a half-controlled bridge circuit.
Firing angle limitation
The firing angle limitations in the factory settings are p50250 = 0 degrees for Alpha G and
p50251 = 180 degrees for Alpha W.
If the field winding has a low nominal voltage, Alpha G can be set to higher values to limit the
maximum output voltage in the case of a fault and thus protect the field winding of the motor
from overload. For calculation, see below.
Gating unit
The gating unit synchronizes to the line voltage of the field supply (measured on 3U1/3W1 on
the field module) and, according to the current firing angle, supplies the firing pulses for the
thyristors for the generation of the variable output DC voltage to inject the required load
current.
Optimizing the controller with optimization runs
.Optimization runs provide effective support for controller optimization. See Section 8.2 of the
Operating Instructions.
For optimization runs set p010 = 0.
Possible faults during the optimization runs are F60050 or F60052. The causes are
described in r50047[0] (fault value)
Field current controller optimization run p50051 = 24:
Armature current controller optimization P50051= 25. This optimization run must be executed
whenever possible and results in nearly all cases in sufficient optimization of the current
control loops. If a permanently excited DC motor (excitation via permanent magnets in the
motor stator) is used, the rotor must be locked during current controller optimization.
