Copley Controls Xenus Plus Series User Manual page 141

Xenus Plus User Guide
T Current Limit Algorithm – Application Example
2
B.1.3: I
2
I T Example: Parameters
2
Operation of the I T current limit algorithm is best understood through an example. For this example,
a motor with the following characteristics is used:
•
Peak Current Limit – 12 A
•
T Time Limit – 1 S
2
I
•
Continuous Current Limit – 6 A
From this information, the I
2
I T setpoint = (12 A
See the example plot diagrams on the next page.
2
I T Example: Plot Diagrams
The plots that follow show the response of a drive (configured w/ I
current command. For this example, DC output currents are shown in order to simplify the
waveforms. The algorithm essentially calculates the RMS value of the output current, and thus
operates the same way regardless of the output current frequency and wave shape.
A)
B)
At time 0, plot diagram A shows that the actual output current follows the commanded current. Note
that the current is higher than the continuous current limit setting of 6 A. Under this condition, the I
Accumulator Variable begins increasing from its initial value of zero. Initially, the output current
linearly increases from 6 A up to 12 A over the course of 1.2 seconds. During this same period, the
2
I T Accumulator Variable increases in a non-linear fashion because of its dependence on the square
of the current.
Copley Controls
2
T setpoint is:
–6 A
2 2
) * 1 S = 108 A
2
I T current limit
16
14
12
10
8
6
4
2
0
0 1 2
2
I T Accumulator
120
100
80
I^2T Setpoint
60
I^2T Accumulator
40
20
0
0 1 2
2
S
2
T setpoint = 108 A
I_commanded
I_actual
3 4 5 6
Tim e (S)
3 4 5 6
Tim e (S)
16-01344 Rev 06
2
S) to a given
7
7
2
T
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