Siemens Simovert Masterdrives Compendium page 916

Engineering Information
Induction
servomotors
11-16
In order to calculate the motor's rms current, the motor torque in all
parts of the travel curve must first be determined. The motor current is
thus calculated as follows:
M
Mot 2
= ⋅
I I ( )
Mot n
M
n
I Rated magnetizing current
µ
n
= 1
k In the constant flux range
n
n
=
k In the field weakening range
n
n
n
The rms value of the motor current is calculated as follows:
+
I
Mot A
∑
(
2
=
I
eff
+
I I
Mot A Mot E
Mean motor current in time segment ∆ t
2
(A: initial value, E: final value)
n
Mot
n
n
∆
t
i
I
I
Mot A
I
Mot
∆
t
i
Fig. 11-10 Example of motor speed and motor current in a time segment
If the dynamic limits are being adhered to and the rms value of the
motor current is smaller than the motor's rated current, the selected
induction servomotor can be used.
I I
µ µ
n
2 2
⋅ − ⋅ +
( 1 ( ) ) k (
n
I I
n
I
Mot E
2
⋅ ∆
) t
i
T
Field weakening range
(Increase of the motor current in the field weakening
Mot E
range)
6SE7087-6QX70 (Version AE)
Compendium Motion Control
06.2005
1
n
2
⋅
)
2
k
n
n
i
t
t
∆
t i
Siemens AG
SIMOVERT MASTERDRIVES