User manual

3U Servo Amplifier
DC BRUSH MOTOR DRIVE SETUP WITH TURBO PMAC
Commutation Phase Angle: Ixx72
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 over current 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.
Special Instructions for Direct-PWM Control of Brush Motors
Special settings are needed to use the direct-PWM algorithms for DC brush motors. The basic idea is to
trick the commutation algorithm into thinking that the commutation angle is always stuck at 0 degrees, so
current into the A phase is always quadrature (torque-producing) current. These instructions assume:
The brush motor’s rotor field comes from permanent magnets or a wound field excited by a separate
means; the field is not controlled by one of the phases of this channel.
The two leads of the brush motor’s armature are connected to amplifier phases (half-bridges) that are
driven by the A and C-phase PWM commands from Turbo PMAC. The amplifier may have an
unused B-phase half-bridge, but this does not need to be present.
The following settings are the same as for permanent-magnet brushless servo motors with an absolute
phase reference:
Ixx01 = 1 (commutation directly on Turbo PMAC) or Ixx01=3 (commutation over the MACRO ring)
Ixx02 should contain the address of the PWM A register for the output channel used or the MACRO
Node register 0 (these are the defaults), just as for brushless motors.
Ixx29 and Ixx79 phase offset parameters should be set to minimize measurement offsets from the A
and B-phase current feedback circuits, respectively.
Ixx61, Ixx62, and Ixx76 current loop gains are set just as for brushless motors.
Controller Setup 31