AFX SERIES® OPERATION MANUAL
SECTION 6:
Entire Contents Copyright
2018 by Pacific Power Source, Inc. (PPS)
• All Rights Reserved • No reproduction without written authorization from PPS.
AFX Series Power Source Operation Manual
Page 108 of 402
6.4.9
Peak Current Protection Minimum Setting
The programmable peak current protection feature allows the user to limit the peak current
that is applied to the EUT. In order to do this, the power source has to clamp the output
voltage. The power source will do so when the set limit is exceeded on a switching cycle by
switching cycle bases. There are some practical considerations to take into account as some
of the current delivered by the power source can be absorbed by the internal output filters.
If the peak current limit value is set too low, it may prevent the power source from
delivering the programmed output voltage at higher frequencies. Even if no load is
connected to the power source, some reactive power is required to generate the output
voltage. This reactive current will be limited by the peak protection level set point so a
minimum value applies. The formula that determines the minimum set value for peak
current protection is:
Ipk > 1 A + Vac_setpoint * 0.09 * Freq_setpoint (in kHz).
This formula applies in three phase mode for AFX models of 15kVA and below. For example,
with an output AC voltage setting of 230Vac and a frequency setting of 1000 Hz, the
minimum set value would be:
Ipk min = 1 + 230 * 0.09 * 1 = 21.7 Apeak
If the set value is below this level, the following two conditions will occur:
A)
The voltage measured at the output will be less than desired.
Example 1:
Frequency 400Hz.
Voltage 120Vac.
Peak current limit 1A.
The voltage measured at the output will be limited to 25.6Vrms
Example 2:
Frequency 400Hz.
Voltage 120Vac.
Peak current limit 2A.
The voltage measured at the output will be 54.6Vrms
Example 3:
Frequency 400Hz.
Voltage 120Vac.
Peak current limit 3A.
The voltage measured at the output will be 83.22Vrms
The higher the frequency and the AC voltage set points are, the lower the measured
voltage at the output will be unless the peak current protection level is set high enough
to prevent this condition.
