© ElectroCraft 2022
20
High Power Universal Drive User Manual
4.5
Peak Current Fold-back (I
2
t)
Currents higher than rated continuous current may be required to achieve high momentary torques. The
drive and motor can withstand these higher peak currents for a limited time. To protect the drive and
motor, the drive will limit the time operated with peak current. The protection is implemented as an I
2
t
algorithm with a programmable peak current (I
P
), rated current (I
R
) and I
2
t time which is the peak current
time (T
P
). The values of peak current and continuous current (I
C
) are entered in the drive configuration
software. The drive will not supply current above the peak current value.
The I
2
t algorithm integrates up towards the limit whenever the output current exceeds the continuous I
2
t
current value and integrates down when the output current is below the continuous I
2
t current value.
When the I
2
t algorithm limit is reached, the output current is reduced and limited to the continuous I
2
t
current limit value. The I
2
t time limit allowed by the software is computed using the equation given below.
I
2
t algorithm limit = ((I
P
)
2
– (I
R
)
2
) x T
P
Where, for A24V80A:
I
P
= Peak phase current set by user (maximum of 60 A)
I
R
= Rated phase current of 24 A
T
P
= I
2
t time, in ms
I
2
t algorithm limit = 6048000 (preset)
Where, for A40V24A:
I
P
= Peak phase current set by user (maximum of 100 A)
I
R
= Rated phase current of 40 A
T
P
= I
2
t time, in ms
I
2
t algorithm limit = 16800000 (preset)
The I
2
t time limit that the software allows is 2 seconds for a peak current and beyond that the drive limits
the current to the I
2
t continuous current set in the configuration software. The allowable I
2
t time limit
increases when the desired peak current value reduces.
Result of the I
2
t algorithm at maximum peak current and continuous current is shown in Figure 7.
20
60
C
ur
re
nt
(A
)
1
2
3
4
5
6
Time (s)
I
2
t limits current to
20 A after 2 seconds
(For A24V80A)
33
100
C
ur
re
nt
(A
)
1
2
3
4
5
6
Time (s)
I
2
t limits current to
33 A after 2 seconds
(For A40V24A)
Figure 7: I
2
t Algorithm Example
The I
2
t time limit is computed by the software and any time value entered within the time limit computed is
accepted by the software. If the entered time value is longer than the computed time limit, the software
defaults to the computed time limit. Additionally, there is a preset maximum I
2
t time limit of 30 seconds.
