Variable Maximums applied to the current limits
The variable maximums applied to the current limit parameters are VM_MOTOR1_CURRENT_LIMIT for motor map 1 and
VM_MOTOR2_CURRENT_LIMIT for motor map 2. The calculations given below are used in each drive mode to define
VM_MOTOR1_CURRENT_LIMIT. Similar calculations based on the equivalent motor map 2 parameters are be used to define
VM_MOTOR2_CURRENT_LIMIT.
The diagram shows a motor operating with a current equal to I
MaxRef
, which was defined in the previous section. The magnetising and torque producing
motor currents are defined for rated conditions as follows.
I
Rated
= Rated Current (05.007)
cos φ = Rated Power Factor (05.010)
The angle between the total current vector and the torque producing current (cos φ) is assumed to be equivalent to the power factor. The power factor
is really the angle between the voltage and current vectors. Normally for Open-loop operation the difference between the power factor and cos f is small
and can be neglected. Therefore
Rated magnetising current I
Mrated
= I
Rated
sin φ
Rated torque producing current I
Trated
= I
Rated
cos φ
Assuming that the magnetising current does not change with load then when the motor operates with maximum allowed current (I
MaxRef
) the torque
producing current is given by:
I
Tlimit
= I
MaxRef
x cos(sin
-1
(I
Mrated
/ I
MaxRef
))
The maximum required current limit setting is given by:
VM_MOTOR1_CURRENT_LIMIT = (I
Tlimit
/ I
Trated
) x 100%
As mentioned previously the magnetising current does vary slightly with load, but the headroom between I
MaxRef
and the peak limit should allow for this.
Parameter 04.001 Current Magnitude
Short description Shows the instantaneous drive output current
Mode Open‑Loop
Minimum −VM_DRIVE_CURRENT_UNIPOLAR Maximum VM_DRIVE_CURRENT_UNIPOLAR
Default Units A
Type 32 Bit Volatile Update Rate 4ms write
Display Format Standard Decimal Places 3
Coding RO, FI, VM, ND, NC, PT
Current Magnitude (04.001) is the instantaneous drive output current scaled so that it represents the r.m.s. phase current in Amps under steady state
conditions.
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