Reference Manual

PMAC 2 Software Reference
PMAC I-Variable Specification 93
• I357 is set to 32,768 * 20/50 = 13,107.
3. PMAC Motor 4 is driving a sine-wave mode amplifier that has a gain for each phase
input of 5 amps/volt. The amplifier has a continuous rating of 20 amps (RMS); the
motor has a continuous rating of 22 amps (RMS).
• PMAC’s maximum output of 32,768, or 10 volts, corresponds to 50 amps peak in a
phase.
• The amplifier has the lower continuous current rating, so we use its limit of 20
amps (RMS).
• 20 amps (RMS) corresponds to peak phase currents of 20*1.414 = 28.28 amps.
• I457 is set to 32,768 * 28.28 / 50 = 18,534.
4. PMAC Motor 6 is driving a direct-PWM power block amplifier for an AC motor. The
A/D converters in the amplifier are scaled so that a maximum reading corresponds to
50 amps of current in the phase. The amplifier has a continuous current rating of 20
amps (RMS), and the motor has a continuous rating of 15 amps (RMS).
• PMAC’s maximum ADC phase reading of 32,768 corresponds to 50 amps.
• The motor has the lower continuous current rating, so we use its limit of 15 amps
(RMS).
• 15 amps (RMS) corresponds to peak phase currents of 15*1.414 = 21.21 amps.
• 21.21 amps corresponds to an ADC reading of 32,768 * 21.21/50 = 13,900.
• I657 should be set to 13,900 * 0.866 = 12,037.
See Also
Integrated Current Protection (Making Your Application Safe)
I-Variables Ix58, Ix69
Ix58 Motor x Integrated Current Limit
Range
0 .. 8,388,607
Units
2
30
(DAC bits)
2
• servo cycles
{bits of a 16-bit DAC}
Default
0
Remarks
Ix58 sets the maximum integrated current limit for PMAC’s I
2
T integrated current limiting
function. If Ix58 is 0, the I
2
T limiting function is disabled. If Ix58 is greater than 0,
PMAC will compared the time-integrated difference between the squares of commanded
current and the Ix57 continuous current limit to Ix58. If the integrated value exceeds Ix58,
then PMAC faults the motor just as it would for receiving an amplifier fault signal, setting
both the amplifier-fault and the I
2
T-fault motor status bits.
The Ix58 limit is typically set by taking the relationship between the instantaneous current
limit (Ix69 on PMAC, in units of a 16-bit DAC), the magnetization current (Ix77; typically
0 except for vector control of induction motors) and the continuous current limit (Ix57 on
PMAC, in units of a 16-bit DAC) and multiplying by the time permitted at the
instantaneous limit. The formula is:
(sec)imePermittedT)Hz(eRateServoUpdat
2
32768
2
57Ix
2
77Ix
2
69Ix
58Ix ∗∗
−+
=
Refer to the section Making Your Application Safe in the User’s Guide for a more detailed
explanation of I
2
T protection.