User's Manual

PMAC2 User Manual
30 Setting Up PMAC2 for Direct PWM Control
Example:
The following table shows the results for a sample run of this test.
Step M102 (A) M104 (B) M107 (C) Cycle
Position
Physical
Position
M101
(Counts)
M105 (A) M106 (B)
1 +500 0 -500
0
o
e
4:00 8820 < 0
≈ 0
2 +500 -500 0
+60
o
e
3:00 9184 < 0 > 0
3 0 -500 +500
+120
o
e
2:00 9501
≈ 0
> 0
4 -500 0 +500
+
180
o
e
1:00 9845 > 0
≈ 0
5 -500 +500 0
-120
o
e
12:00 10218 > 0 < 0
6 0 +500 -500
-60
o
e
11:00 10532
≈ 0
< 0
1 +500 0 -500
0
o
e
10:00 10869 < 0
≈ 0
From this test, we can conclude:
• PWM operation is fundamentally working (we have six approximately equal steps)
• We have a 4-pole motor because we moved 1/2 revolution
• Current ADC inputs are working: we got proportionate responses
• Sign of current is opposite to sign of voltage, so Ix72 should be 85.
• We move 2049 counts in one cycle, so 4096 counts per revolution should be correct
• Encoder counter increased, so commutation polarity is correct
Cleaning Up
When done with this section of the testing, write zero values into the command registers and disable the
amplifier with the command:
M102=0 M104=0 M107=0 M114=0
With zero commands into all of the phases of the drive, with the drive either enabled or disabled, the
ADC registers should read nearly zero. PMAC2 can compensate for non-zero values with the offset
parameters Ix79 (A-phase offset) and Ix29 (B-phase offset). These offset parameters should hold values
of the opposite sign of the phases' ADC values when there are zero PWM commands. Ix29 and Ix79
magnitudes assume 16-bit values; since we are using 16-bit M-variables to look at the ADC registers,
regardless of the true resolution of the ADCs, we can just read the M-variable values at zero command
and use the opposite values for Ix79 and Ix29.
Debugging
With zero commands on the three output registers, observe any of the six PWM output signals with an
oscilloscope . All six should have 50% duty cycle (minus the deadtime set by I904) at the frequency set
by I900. All three top PWM signals should be in phase with each other. All three bottom PWM signals
should be in phase with each other, and one-half cycle out of phase with the top signals. Observing a top
and bottom pair, you should be able to observe the deadtime between the top and bottom on times.
With a positive command into the A-phase, a negative command into the B-phase, and a zero command
on the C-phase, these waveforms should change. On the oscilloscope, you should observe PWMATOP1
on-time increase, and PWMABOT1 on-time decrease, while maintaining the deadtime. Similarly,
PWMBTOP1 on-time should decrease, and PWMBBOT1 on-time should increase, maintaining the
deadtime between them.
If the analog voltages representing the current measurements are available, these can be probed for
diagnostic purposes. Many direct PWM drives provide analog current measurement outputs and the A/D
conversion is done on an interface board; for these drives, the probing is easy. If the A/D conversion is
done inside the drive, access to test points to probe these voltage levels. Consult the drive manual for
location and scaling of these signals.