User guide

Regen Resistor Sizing and Configuration Xenus XTL User Guide
148 Copley Controls Corp.
I
2
T Example: Plot Diagrams
The plots that follow show the response of an amplifier (configured w/ I
2
T setpoint = 108 A
2
S) to a
given 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)
I
2
T current limit
0
2
4
6
8
10
12
14
16
01234567
Time (S)
Current (A)
I_commanded
I_actual
B)
I
2
T Accumulator
0
20
40
60
80
100
120
01234567
Time (S)
I
2
T energy (A
2
-S)
I^2T Setpoint
I^2T Accumulator
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
2
T 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 I
2
T Accumulator Variable increases in a non-linear fashion because of its dependence
on the square of the current.
At about 1.6 seconds, the I
2
T Accumulator Variable reaches a values equal to the I
2
T setpoint. At
this time, the amplifier limits the output current to the continuous current limit even though the
commanded current remains at 12 A. The I
2
T Accumulator Variable value remains constant during
I
2
T Setpoint
I
2
T Accumulator