User's Manual

PMAC2 User Manual
Setting Up PMAC2 Commutation (Direct PWM or Sine Wave) 39
SETTING UP PMAC2 COMMUTATION (DIRECT PWM OR SINE
WAVE)
Operation of the Digital Current Loops
By this point, proper operation of the digital current loops should be established for direct PWM control,
or basic operation should be established for analog sine-wave control. The commutation I-variables Ix70
and Ix71 (commutation cycle size), Ix72 (commutation phase angle), and Ix83 (commutation feedback
address) should already be set properly.
The next steps, explained in this section, are common for both types of control, with a shared
commutation algorithm.
Confirming Commutation Polarity Match
For the PMAC2 commutation algorithms to work properly, the polarity of the output phases must match
the feedback polarity. If there is a mismatch, the algorithm will lock up the motor at a point of zero
torque. For a synchronous motor, we tested the polarity match in previous sections, but we can confirm
the results here. For an asynchronous induction motor, we may be testing the polarity for the first time
here. The test to see whether there is a match is simple, and slightly different for synchronous and
asynchronous motors.
Synchronous Motor Test
With a synchronous motor, we try applying both a direct current command and a quadrature current
command. Because we have not established a phase reference yet, we cannot be sure that a quadrature
current command really produces quadrature current. But if the commutation polarity is correct, at least
one of the commands should cause steady movement of the motor.
First, we apply a direct current command with:
Ix77=3000 O0 ; ~10% direct current command
If this does not produce steady movement, we apply a quadrature current command with:
Ix77=0 O10 ; 10% quadrature current command
To finish the test, we issue a K command and make sure Ix77 has been returned to 0.
If one of these commands produces steady movement, the commutation polarity is correct, and we can
move on to the next stage of establishing a phase reference. However, if neither of these commands
produces steady motion, we probably have commutation polarity mismatch. To correct the mismatch,
refer to the Correcting Polarity Mismatch, Synchronous and Asynchronous Motors sections below.
Asynchronous Motor Test
For an asynchronous AC induction motor, we apply direct and quadrature current simultaneously. We do
this with a command such as
Ix78=3000 Ix77=3000 O10
The actual values may need to change depending on the rotor time constant. Finish the test with a K
command.
If this command produces steady movement, the commutation polarity is correct, and we can move on to
the next stage of optimizing magnetization current and slip gain. However, if we do not get steady
motion, we probably have commutation polarity mismatch (although if the motor cannot be made to move
in either direction, try varying Ix77 and Ix78 by factors of two in both directions). To correct the
mismatch, see the next section.