System Manual – MOVIDRIVE® compact Drive Inverters
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Motor selection for asynchronous AC motors (VFC)
Project Planning
Speed/torque
characteristic
curve
The field weakening range starts when the set maximum output voltage of the inverter
is reached. Consequently, the speed range of the motor is divided into two ranges:
•
Basic speed range
→
constant torque with increasing power.
•
Field weakening range
→
constant power with an inversely proportionate decrease
in torque.
When determining the maximum speed in the field weakening range, note that the rated
torque M
N
(in relation to the rated speed, e.g. n
N
= 1,500 1/min) falls in inverse propor-
tion and the breakdown torque M
K
is reduced in an inverse quadratic relationship. The
M
K
/M
N
ratio is a motor-specific parameter. The MOVIDRIVE
®
breakdown protection lim-
its the speed when the maximum possible torque is reached.
With gearmotors, the maximum motor speed depends on the size and mounting position
of the gear unit. The speed should not exceed 3,000 1min due to the resulting noise and
oil churning losses.
Dynamic applica-
tions (P
inverter
greater than
P
motor
)
•
The startup function sets the current limit of the inverter (P303/P313) to 150 % of the
rated motor current. The value of the current limit is based on the rated inverter cur-
rent. 150% of the rated motor current is, therefore, less than 150 % of the rated in-
verter current (value of P303 P313). For dynamic applications, this parameter must
be set manually to a higher value.
•
The startup function sets the slip compensation parameter (P324/P334) to the rated
slip of the motor. In the case of VFC-n-CONTROL, the internal slip limiting function
allows the slip to reach max. 150 % of this setting. Consequently, the motor develops
at most 150 % of the rated motor torque. For higher torque ratings, the slip compen-
sation parameter (P324) must be increased accordingly.
01729BEN
Figure 59: Quadratically falling breakdown torque
0
1500 1800 2100
2400
2700 3000
3300 3600
0
M
N
M
M
N
M = 1.8 M
K
N
M = 2.2 M
K
N
M = 2.5 M
K
N
M = 2.8 M
K
N
M = 3.0 M
K
N
0.5
1.0
1.5
2.0
2.5
3.0
Armature range
Field weakening range
n / rpm
NOTE
Set parameter P324 "Slip compensation" to max. 130 % of the rated slip of the motor
for stable operation.
Summary of Contents for MOVIDRIVE compact MCH41A
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