Siemens SIMOVERT MASTERDRIVES Manual page 875

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