User's Manual

Geo MACRO Drive User and Reference Manual
Turbo PMAC2 Related I-Variable Reference 123
Ixx70, Ixx71: Commutation Cycle Size
If the Turbo PMAC2 is performing commutation for Motor xx, providing either 2-phase current commands
(sine-wave output) or 3-PWM phase voltage commands (direct PWM output), the size of the commutation
cycle is equal to Ixx71/Ixx70, normally expressed in encoder counts. Because the MACRO station
provides position feedback in units of 1/32 count for both servo and commutation, the value of Ixx70 and
Ixx71 must be set to provide a ratio 32 times the number of true counts in the commutation cycle.
For example, if the commutation cycle has 1000 encoder counts, Ixx70 could be set to 1 and Ixx71 could
be set to 32,000.
Ixx72: Commutation Phase Angle
Ixx72 controls the angular relationship between the phases of a multiphase motor. When Turbo PMAC is
closing the current loop digitally for Motor xx, the proper setting of this variable is dependent on the
polarity of the current measurements.
If the phase current sensors and ADCs in the amplifier are set up so that a positive PWM voltage
command for a phase yields a negative current measurement value, Ixx72 must be set to a value less than
1024: 683 for a 3-phase motor, or 512 for a DC brush motor. If these are set up so that a positive PWM
voltage command yields a positive current measurement value, Ixx72 must be set to a value greater than
1024: 1365 for a 3-phase motor, or 1536 for a DC brush motor. The testing described below shows how
to determine the proper polarity.
The direct-PWM algorithms in the Turbo PMAC are optimized for 3-phase motors and will cause
significant torque ripple when used with 2- or 4-phase motors. Delta Tau has created user-written phase
algorithms for these motors; contact the factory if interested in obtaining these.
Note:
It is important to set the value of Ixx72 properly for the system. Otherwise, the
current loop will have unstable positive feedback and want to saturate. This could
cause damage to the motor, the drive, or both, if overcurrent shutdown features do
not work properly. If unsure of the current measurement polarity in the drive,
consult the Testing PWM and Current Feedback Operation section of this manual.
For commutation with digital current loops, the proper setting of Ixx72 is unrelated to the polarity of the
encoder counter. This is different from commutation with an analog current loops (sine-wave control), in
which the polarity of Ixx72 (less than or greater than 1024) must match the encoder counter polarity.
With the digital current loop, the polarity of the encoder counter must be set for proper servo operation;
with the analog current loop, once the Ixx72 polarity match has been made for commutation, the servo
loop polarity match is guaranteed.
Ixx75: Absolute Phase Position Offset
If Ixx81 (see below) is set to a value greater than zero, then PMAC will read an absolute sensor for
power-on phase position. In this case, it will use Ixx75 to determine the difference between the absolute
sensor’s zero position and the phase commutation cycle’s zero position (unless Hall commutation sensors
are used, in which case Ixx91 contains the initial offset information, which needs to be corrected later).
Normally, this position difference in Ixx75 is expressed in counts multiplied by Ixx70. However, when
the absolute position is read from the position feedback register, as from a Yaskawa absolute encoder
through an Acc-8D Option 9 and the MACRO Station, then Ixx75 is expressed in units of 1/32 of a count
multiplied by Ixx70.