Reference Manual

Turbo PMAC/PMAC2 Software Reference
Turbo PMAC Global I-Variables 130
A commutation cycle, or electrical cycle, consists of two poles (one pole pair) of a multiphase motor.
Note:
In firmware revisions V1.938 and older, the maximum value of Ixx71 was
8,388,607.
Examples:
1. A four-pole brushless motor with a 1000-line-per-revolution encoder andtimes-4” decode has 2
commutation cycles per revolution and 4000 counts per revolution. Therefore, either Ixx70=2 and
Ixx71=4000 could be used, or Ixx70=1 and Ixx71=2000.
2. A linear motor has a 60.96-mm (2.4-inch) electrical cycle. An encoder with a 40 micron pitch is
wired directly into PMAC and “times-4” decode is used. Ixx70 can be set to 1 and Ixx71 can be
calculated as:
cycle
counts
6096
line
counts
4*
mm04.0
line
*
cycle
mm
96.6071Ixx
3. An 8-pole brushless motor has an 8192-line encoder that is wired into a Compact MACRO Station
withtimes-4” decode. The position data is sent back to PMAC in the MACRO “Type 1” protocol,
with units of 1/32 count. If Ixx70 is set to 4 (for 4 electrical cycles per revolution), Ixx71 can be
calculated as:
line
)count32/1(
144,262
count
)count32/1(
32*
line
counts
4*
cycles4
rev
*
rev
lines
819271Ixx
See Also:
I-variables Ixx01, Ixx70, Ixx72-Ixx83
Setting Up Turbo PMAC Commutation
Ixx72 Motor xx Commutation Phase Angle
Range: 0 2047
Units: 360/2048 elec. deg. (1/2048 commutation cycle)
Default: 1365 (= -120
o
e or 240
o
e)
For a Turbo PMAC-commutated motor, Ixx72 sets the angular distance between the phases of a
multiphase motor. The units of Ixx72 are 1/2048 of an electrical cycle. The usual values to be used are:
3-phase: 683 or 1365 (+/- 120
o
e)
2- or 4-phase: 512 or 1536 (+/- 90
o
e)
For a given number of phases, the proper choice of the two possible values is determined by the polarity
match between the output commands and the feedback, as detailed below. Typically, the choice is made
automatically by the Turbo Setup expert-system program on the PC.
Ixx72 is used slightly differently depending on whether Turbo PMAC is performing current-loop
calculations as well as commutation. Both cases are explained below:
1. Turbo PMAC performing commutation, but not current loop: When Turbo PMAC is not
performing digital current loop closure for Motor xx (Ixx82=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 I7mn0 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.