Delta Tau GEO BRICK LV User Manual

Evaluating the Polarity Match 

Determine the proper setting of Ixx72 by looking at the direction of motion between the two steps.  If the 
position changed in the negative direction, set Ixx72 less than 1024 – to 683 for a 3-phase motor, or 512 
for a 2- or 4-phase motor.  If the position changed in the positive direction, set Ixx72 greater than 1024 – 
to 1365 for a 3-phase motor, or 1536 for a 2- or 4-phase motor. 
For the motor in this example, we conclude that we want a value of 512 if it is a 4-phase motor or 683 if it 
is a 3-phase motor.  If the encoder direction is subsequently changed for system reasons, change I172 to 
match. 

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 
Ixx70 and Ixx71 (commutation cycle size), Ixx72 (commutation phase angle), and Ixx83 (commutation 
feedback address) already should be set properly.   
The next steps, explained in this section, are common for both types of control, with a shared 
commutation algorithm. 

For the Turbo PMAC 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.   

Testing Commutation Polarity Match 

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: 

Ixx77=3000 O0 

; ~10% direct current command 

If this does not produce steady movement, we apply a quadrature current command with: 

Ixx77=0 O10 

; 10% quadrature current command 

To finish the test, we issue a K command and make sure Ixx77 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, see 
Correcting Polarity Mismatch, below. 

Correcting Polarity Mismatch 

To correct a commutation polarity mismatch, there are two possible options: 
1.  Reverse the feedback direction sense by changing I7mn0.  However, this changes the direction sense 

of the axis, which may not be tolerable. 

2.  Reverse the output direction sense.  For analog sine-wave output, this can be done by changing Ixx72, 

for example from 1365 to 683, or by exchanging two phase leads between amplifier and motor. For 
direct PWM, this must be done by exchanging phase leads.  Usually this is done at the screw 
terminals on the amplifier.  Exchanging any two phases will change the polarity in the same way.  
However, the relationship between the sensor zero position and Turbo PMAC’s commutation cycle 
zero position is dependent on which two phases are exchanged. 

After changing the polarity match by one of the above methods, repeat the test to make sure that the 
problem has been solved.