Reference Manual

Turbo PMAC/PMAC2 Software Reference
Turbo PMAC Global I-Variables 122
4. Turbo 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 an Application Safe)
I-Variables Ixx58, Ixx69
Ixx58 Motor xx Integrated Current Limit
Range: 0 - 8,388,607
Units: 2
30
(DAC bits)
2
 servo cycles
{Bits of a 16-bit DAC/ADC}
Default: 0
Ixx58 sets the maximum integrated current limit for Turbo PMAC’s I
2
T or |I|T integrated current limiting
function. If Ixx58 is 0, the I
2
T limiting function is disabled. If Ixx58 is greater than 0, Turbo PMAC will
compare the time-integrated difference between the commanded or actual current and the Ixx57
continuous current limit to Ixx58. If Ixx57 is greater than 0, Turbo PMAC uses the squares of these
current values for I
2
T limiting; if Ixx57 is less than 0, Turbo PMAC uses the absolute value of these
current values for |I|T limiting. If the integrated value exceeds the limit set by Ixx58, then Turbo PMAC
faults the motor just as it would for receiving an amplifier fault signal, setting both the amplifier-fault and
the integrated-current-fault motor status bits.
Typically, the Ixx58 limit is set by taking the relationship between the instantaneous current limit (Ixx69
on Turbo PMAC, in units of a 16-bit DAC), the magnetization current (commanded by Ixx77; typically 0
except for vector control of induction motors) and the continuous current limit (|Ixx57| on Turbo PMAC,
in units of a 16-bit DAC) and multiplying by the time permitted at the instantaneous limit.
When using I
2
T limiting (Ixx57 > 0), the formula is:
(sec)imePermittedT)Hz(eRateServoUpdat
2
32768
2
57Ixx
2
77Ixx
2
69Ixx
58Ixx 


When using |I|T limiting (Ixx57 < 0), the formula is:
(sec)imePermittedT)Hz(eRateServoUpdat
32768
57Ixx
2
77Ixx
2
69Ixx
58Ixx 


Refer to the Making the Application Safe section in the User manual for a more detailed explanation of
I
2
T and |I|T protection.
Example:
For I
2
T limiting, with the instantaneous current limit Ixx69 at 32,767, the magnetization current Ixx77 at
0, the continuous current limit Ixx57 at 10,589 (1/3 of max), the time permitted with maximum current at
1 minute, and the servo update rate at the default of 2.25 kHz, Ixx58 would be set as
120000602250)
2
33.0
2
0.0
2
0.1(58Ixx 