Installation manual

GEO Direct PWM Amplifiers – Preliminary Documentation
Troubleshooting 31
SETTING I
2
T PROTECTION
It is very important to set the I
2
T protection for the amplifier/motor system for PMAC2 direct PWM
commutation. Normally, an amplifier has internal I
2
T protection because it is closing the current loop.
When PMAC2 is closing the current loop, the amplifier cannot protect itself or the motor from over
heating. Either set up the I
2
T protection using one of the Setup Programs or manually set the Ixx69,
Ixx57 and Ixx58 variables based on the following specifications:
Parameter Description Notes
MAX ADC Value
Maximum Current output of amplifier relative to a
value of 32767 in Ixx69
Part of amplifier specification
Instantaneous Current
Limit
The lower of the amplifier or motor system RMS or Peak*
Continuous Current
Limit
The lower of the amplifier or motor system Usually RMS
I
2
T protection time Time at instantaneous limit Usually two seconds
Magnetization Current Ixx77 value for induction motors Only for induction motors
Servo Update
Frequency
Default is 2258 Hz.
* If specification given in RMS, calculate this value by 1.41 to obtain peak current for calculations.
Example Calculations for Direct PWM commutated motor:
MAX ADC = 18A
Instantaneous Current Limit = 18A Peak
Continuous Current Limit = 7A RMS
I
2
T protection time = 2 seconds
Magnetization Current (Ixx77) = 0
Servo Update = 2.258 kHz
32767x
ADCMAX
)Peak(LimiteoustansIn
69Ixx =
if calculated Ixx69>32767 then Ixx69 equals 32767
(
)
o
30xCos32767x
LimiteoustansIn
LimitContinuous
57Ixx =
)onds(secTime)Hz(encyServoFrequ
2
32767
2
57Ixx
2
77Ixx
2
69 Ixx
58Ixx ××
−−
=
Based on the above data and equations, the following results: Ixx69=32767
Ixx57=11035
Ixx58=4004
For details about I
2
T protection, refer to the safety sections of the User Manual. Details about the variable
setup can be found in the Software Reference manual.