Reference Manual

PMAC 2 Software Reference
PMAC I-Variable Specification 103
Ix72 Motor x Commutation Phase Angle
Range
0 .. 255
Units
360/256 elec. deg. (1/256 commutation cycle)
Default
85 (=120
o
e)
Remarks
For a PMAC-commutated motor (Ix01 = 1), Ix72 set the angular distance between the
phases of a multiphase motor. The usual values to be used are:
3-phase: 85 or 171 (+/- 120
o
e)
2- or 4-phase: 64 or 192 (+/- 90
o
e)
For a given number of phases, determining which of the two possible settings is to be used
depends on whether the PMAC is also closing the current loop for the motor.
1. PMAC performing commutation, but not current loop
When PMAC is not performing digital current loop closure for Motor x (Ix82 = 0), the
output direction sense determined by this parameter and the motor and amplifier phase
wiring must match the feedback direction sense as determined by the encoder-decode
variable 0 (I900, I905, etc. on a PMAC(1); I9n0 on a PMAC2) and the encoder wiring. If
the direction senses do not match proper commutation and servo control will be
impossible; the motor will lock into a given position.
For these systems, changing between the two values for a given number of phases has the
same effect as exchanging motor leads, which changes the motor’s direction of rotation for
a given sign of a PMAC2 torque command.
Refer to the section Setting Up PMAC Commutation for tests to determine the proper Ix72
setting. For systems without PMAC2 digital current loop closure, once this
commutation/feedback polarity has been properly matched, the servo/feedback polarity
will automatically be properly matched.
2. PMAC performing commutation and current loop
When PMAC is performing digital current loop closure for Motor x (Ix82 > 0; PMAC2
only), the output direction sense determined by this parameter must match the polarity of
the phase current sensors and the analog-to-digital conversion (ADC) circuitry that brings
this data into PMAC2. It is independent of motor or amplifier phase wiring, encoder
wiring, and PMAC2 encoder-decode direction sense.
CAUTION:
Do not attempt to close the digital current loops on PMAC2 (O
commands or closing the position loop) until you are sure of the
proper sense of the Ix72 setting. An Ix72 setting of the wrong sense
will cause positive feedback in the current loop, leading to
saturation of the PMAC outputs and possible damage to the motor
and or amplifier.
For these systems with a PMAC2 digital current loop, if the phase-current ADC registers
report a positive value for current flowing into the phase (i.e. the PWM voltage command
value and the current feedback value have the same sign), Ix72 must be set to a value
greater than 128 (usually 171 for a 3-phase motor, or 192 for a 2- or 4-phase motor). If the
phase-current ADC registers report a positive value for current flowing out of the phase
(i.e. the PWM voltage command value and the current feedback value have opposite
signs), Ix72 must be set to a value less than 128 (usually 85 for a 3-phase motor, or 64 for
a 2- or 4-phase motor).