January 2012 6.19 Configuring the Controller Unit and Drive Motors 1051
Reduction of the reference value for I
2
t monitoring or rated current I
N
in
the table of power modules
The reduction of the rated current I
N
of the power modules, as well as the
reference value for I
2
t monitoring can be calculated from two values (X1, X2)
that are given in the SIEMENS documentation.
The percent reduction of the rated current can be calculated with the following
formula:
X1 = Reduction factor of the current in % at a PWM frequency of 8 kHz
X2 = PWM threshold frequency in kHz at which the electrical power
reduction begins
f
PWM
= PWM frequency in kHz set in MP_ampPwmFreq
This results in the reference value for I
2
t monitoring:
Reduce the rated current values I
N
of your power modules in the power
module table.
or
Reduce the reference value (CfgServoMotor/motFactorI2t) for the I
2
t
monitoring.
X
R
[%] 100
100 X1–()8 kHz f
PWM
–()⋅
8 kHz X2–
---------------------------------------------------------------------------------------- X 1+
⎝⎠
⎛⎞
–=
X
B
1
X
R
[%]
100
--------------------
–=
A reduction of the rated current of the power module can cause a reduction
of the rated torque and, as a consequence, the rated power of the motor,
if equal values for rated current of the power module and the rated current
of the motor were chosen.
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