6 – 468 HEIDENHAIN Technical Manual TNC 426, TNC 430
For the commissioning of new machines, HEIDENHAIN recommends
adjusting the PWM frequency to fit axis modules (normally 4 kHz, see
SIEMENS documentation). If the power module of the spindle gets too warm
in spite of a reduction of the PWM frequency from 5 kHz to 4 kHz, then the
reference value for the I
2
t monitoring (MP2303) or the rated current I
N
must
be reduced.
Reduction of the reference value for the I
2
t monitoring or the rated
current I
N
The reduction of the rated current I
N
of the power modules, as well as the
datum 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:
n X1 = Reduction factor of the current in % at a PWM frequency of 8 kHz
n X2 = PWM threshold frequency in kHz at which the electrical power
reduction begins
n f
PWM
= PWM frequency in kHz set in MP2180.0-8
This results in the reference value for I
2
t monitoring:
Example for a 50-A power module:
n Axis power module with 50 A, PWM frequency of 5 kHz, X1 = 40 %, X2 =
4 kHz
n Spindle power module with 50 A, PWM frequency of 5 kHz, X1 = 40 %, X2
= 3.2 kHz
Note
A reduction of the PWM frequency has no effect on the maximum speed,
but it means that the axis and the spindle without integral DSP must be
commissioned again.
X
R
[%] 100
100 X1–()8 kHz f
PWM
–()⋅
8 kHz X2–
-------------------------------------------------------------------------------------------- X 1+
èø
æö
–=
X
B
1
X
R
[%]
100
--------------------
–=
X
R
[%] 100
100 40–()8 kHz 5 kHz–()⋅
8 kHz 4 kHz–
---------------------------------------------------------------------------------------- 4 0+
èø
æö
– 15 %==
X
B
1
15
100
-----------
– 085,==
X
R
[%] 100
100 40–()8 kHz 5 kHz–()⋅
8 kHz 3,2 kHz–
---------------------------------------------------------------------------------------- 4 0+
èø
æö
– 22,5 %==
X
B
1
22,5
100
-------------
– 0.78==
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