Additionally Torque Limiting In The Field Weakening Range; Influence Of The Current Limit - KEB COMBIVERT F5-A Applications Manual

of the characteristic to lower speeds.
For value 4 ("on" ), the limiting characteristic is shifted in both directions, to lower speeds at lower voltage, and
to higher speeds at higher voltages.
At this value, the motor achieves maximum torque. It is unfavorable especially at regenerative operation that
the DC link voltage can increase very quickly and in a wide range. These dynamic changes can cause high
disturbance in the field weakening range.
Therefore preferable setting is 8 („>Un(FI) = off, abnormal stopping = off"). Only the necessary physical shifting
of the characteristic due to low DC link voltage is executed here.
That means the characteristic is only shifted if the DC link voltage is lower than the rated DC link voltage (= √
2 * inverter rated voltage).
There is no shifting if the DC link voltage is higher than the rated voltage.
Value 12 („>Un(FI)= off, abnormal stopping= on") can be selected if the maximum achievable torque shall
be available for emergency stop. In this mode the characteristic at higher DC link voltage is shifted to higher
speeds only during emergency stop operation. Generally value "8" should be used if possible.
7.8.3.2.4 Influence of the current limit
The total power of the motor in the field weakening range consists of active current and magnetizing current.
The maximum torque limits only the active current.
For some motors there is a maximum current specified in the data sheet. This is valid for both components
together. Therefore the total motor current can be limited by this parameter.
The magnetization current has priority if both components together exceed the current limit.
Attention:
To ensure that the speed controller can control the drive, active current flow must always be able. Therefore the
magnetizing current limit (dS.13) must be significant lower than the maximum current (dr.37). Maximum dS.13
should be 0.75 x dr.37.
The max. current limit dr.37 is activated via bit 0 of parameter dS.03.
Bit Meaning
max. current-/
0
mode
7.8.3.3 Additionally torque limiting in the field weakening range
Addr. Parameter
1103h dS.03
1125h dS.37
A possibility to limit the maximum torque in the field weakening is via the characteristic dr.39 .. dr47 and the ad-
justments in ds.03 bit1..3. This has the disadvantage that the characteristic must be determined, either abstract
calculated with the "known motor data" or measured at the test stand. Also the consideration of the DC link
© KEB, 2012-10 COMBIVERT F5-A, -E, -H
dS.03: Current-/torque mode
Value Explanation
0: off software-based current limit off
torque
1: on software-based current limit on
Name
Isq limit, Ds.37
usd max modulation ref.
Torque display and -limiting
Default value
off
95%
Value
0 = off
128 = on
0 ... 100 %
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