Engineering Information
06.2005
6SE7087-6QX70 (Version AE)
Siemens AG
11-18
Compendium Motion Control
SIMOVERT MASTERDRIVES
In general, the maximum motor current occurs during the acceleration
phase. At motor torques > M
0
, the motor current may possibly be
higher than calculated with kTn due to saturation effects. In this case,
the motor current is calculated as follows:
I
M
kTn
M
M
M
M
M
I
M
I
Mot
Mot
Mot
=
⋅ −
−
−
⋅ −
⋅
⋅
(
(
)
(
))
max
max
max
1
1
0
0
2
0
0
for M
Mot
> M
0
I
0
Standstill
current
M
max
Maximum permissible motor torque
I
max
Maximum
permissible motor current
♦
For induction servomotors
Calculation of the motor current is as described under 11.4.
Acceleration into the field-weakening range with a constant motor
torque results in the maximum motor current in the field-weakening
range at maximum speed.
The following formula is used to calculate the arithmetic mean of the
motor current:
•
For
synchronous
servomotors
I
M
t
kTn T
Mot mean
Mot i
i
≈
⋅
⋅
∑
∆
M
Mot i
Motor torque in time segment
∆
t
i
T
Cycle
time
•
For induction servomotors
I
I
I
t
T
Mot mean
Mot A
Mot E
i
=
+
⋅
∑
2
∆
I
I
Mot A
Mot E
+
2
Mean motor current in time segment
∆
t
i
(A: initial value, E: final value)
