Commissioning
8.9 Manual optimization
SINAMICS DCM DC Converter
346 Operating Instructions, 12/2018, A5E34763375A
Optimization of closed-loop field-current control
Determining the field circuit resistance (2 options)
Roughly estimate the field circuit resistance from the rated motor data
p50112 = rated excitation voltage/rated excitation current of motor
Determine the field-circuit resistance by comparing the field current setpoint and actual
value
p50112 = 0: Results in a 180° field precontrol output and, therefore, field current
actual value = 0
p50082 = 3: So that the field remains permanently switched on, even when the line
contactor drops out
p50254 = 0 and p50264 = 0: Only field precontrol active; field-current controller
disabled
Set p50102 to rated excitation current.
Increase p50112 until the actual field current (r50035 converted to amperes using
r50073[1]) equals the required setpoint (p50102).
Set p50082 back to the system's operating value.
Overall optimization of closed-loop field-current control
• Checking the precontrol characteristic
Set the function generator to a triangular waveform (0% to 100%), period =
10000 ms
Supply point: p50611[0] (see function diagram 6905)
Set p50082 = 3 (field continuously on)
Record the signals r52271 (output, precontrol) and r52260 (output, field current
controller)
The parameters of the precontrol (Rf [p50112], Lf [p50116] and λf [p51597]) have
been correctly set if the output of the field controller has the lowest possible value
(e.g. less than 5%) over the complete setpoint range.
• Checking the step response
Set the function generator to a squarewave, with
step
height = e.g. 5%
offset = various values, e.g. 80
%
ms
Supply point: p50611[0] (see function diagram 6905)
Set p50082 = 3 (field continuously on)
Record signals r52268 (If-set) and r52265 (If-act)
Change controller parameters Kp (p50255) and Tn (p50256) until the step
response provides a satisfactory result.
The field current controller adaptation can be activated (see function chart 6908) to
eliminate the influence of non-linearity of the field inductance and gating unit.
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