User's Manual

PMAC2 User Manual
Setting Up PMAC2 for Direct PWM Control 29
• For synchronous motors (and possibly for induction motors), the physical change in rotor position
between the initial Step 1 and the return to Step 1 (mark the rotor if necessary) should be equal to 1
pole pair. On a 2-pole motor, it should be one full mechanical revolution. On a 4-pole motor, it
should be one-half mechanical revolution. On a 6-pole motor, it should be one-third mechanical
revolution. On an 8-pole motor, it should be one-fourth mechanical revolution. On a 100-pole motor,
it should be 7.2
o
mech.
Executing the Test
For Motor 1 with a 3-phase motor with 10% voltage commands being acceptable, the commands could be:
M102=0 M104=I900/10 M107=-I900/10 ; Step 1: A0, B+, C-: 0
o
elec.
M102=I900/10 M104=0 M107=-I900/10 ; Step 2: A+, B0, C-: 60
o
elec.
M102=I900/10 M104=-I900/10 M107=0 ; Step 3: A+, B-, C0: 120
o
elec.
M102=0 M104=-I900/10 M107=I900/10 ; Step 4: A0, B-, C+: 180
o
elec.
M102=-I900/10 M104=0 M107=I900/10 ; Step 5: A-, B0, C+: 120
o
elec.
M102=-I900/10 M104=I900/10 M107=0 ; Step 6: A-, B+, C0: -60
o
elec.
M102=0 M104=I900/10 M107=-I900/10 ; Step 1: A0, B+, C-: 0
o
elec.
This test moves the motor through the commutation cycle in the positive direction if Ix72 is less than 128
(e.g. 85); it moves through the cycle in the negative direction if Ix72 is greater than 128 (e.g. 171). On a
synchronous motor, we can use the position reading to check the commutation polarity match; this may
be possible on an induction motor as well.
Action To Take
If the rotor position, as reflected by M101, changed in the wrong direction during this test, we could have
a commutation polarity mismatch. With such a mismatch, the motor would lock in (not run away) when
commanded. There are two possible fixes for this mismatch:
1. Reverse the feedback direction sense by changing I9n0. However, this changes the direction sense of
the axis, which may not be tolerable.
2. Exchange two phase leads between amplifier and motor. Usually, this is done at the screw terminals
on the amplifier. Exchanging any two phases will change the polarity in the same way. However, the
relationship between the sensor zero position and PMAC2's commutation cycle zero position is
dependent on which two phases are exchanged.
For asynchronous induction motors, if the above test did cause proper movement we will have to try each
direction polarity and see which works. This is described below.
Once the commutation polarity match has been established, the servo polarity match is established
automatically. Check this later by seeing that positive O-commands cause motor position to count in the
positive direction.
Remember that if I9n0 is changed later to get the physical direction sense that is desired, exchange the
motor phase leads to re-establish thecommutation polarity match.