Engineering Information 06.2005
6SE7087-6QX70 (Version AE) Siemens AG
11-20 Compendium Motion Control SIMOVERT MASTERDRIVES
In order to determine the arithmetic mean value of the DC link current,
the mean values of the individual inverters are added together. For one
inverter, the calculation is as follows:
I
P
U
Link Inv mean
Mot mean
Mot Inv Link
=
⋅⋅ηη
P
PP
t
T
Mot mean
Mot A Mot E
i
=
+
⋅
∑
2
∆
PP
Mot A Mot E
+
2
Mean motor output in time segment ∆ t
i
[W]
(A: initial value, E: final value)
T Cycle time
Only positive motor outputs are evaluated. When calculating the mean
motor output, one must make sure that the initial value and the final
value of the motor speed do not have different signs. An interpolation
point must therefore exist for every zero passage.
n
Mot
t
t
i
∆
P
Mot
t
t
i
∆
Mot E
P
Mot A
P
Motorized (positive)
Regenerative (negative)
Fig. 11-11 Example of motor speed and motor output in a time segment
∆
t
i
Adding the mean values for the individual inverters gives the mean
value for the rectifiers as follows:
II
Link ct mean Link Inv meanRe
=
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