Delta Tau GEO BRICK LV User Manual

The proportional gain term is expressed as the sum of two I-variables.  Ixx62 is the “forward-path” 
proportional gain term, directly responding to changes in the command values; Ixx76 is the “back-path” 
proportional gain term, directly responding only to the actual current values.  When high position 
feedback resolution is used in the position/velocity loop, the quantization noise in the current command is 
low, and it is better to use Ixx62.  When low position-feedback resolution is used, it is better to use Ixx76.  
Tradeoffs between responsiveness and smoothness can be obtained by varying the amount of the 
proportional gain term allocated to each of these two variables. 

Example: 
The motor has a phase-to-phase resistance of 3.0 ohms, and a phase-to-phase-inductance of 39 
millihenries.  The amplifier phase-current sensors provide their maximum 5-volt output for 17.5 amps of 
current, and the ADCs provide their full-range value for an input of 5V.  The amplifier operates from an 
AC supply voltage of 120Vrms.  The Turbo PMAC is operating at the default phase update frequency of 
9.03 kHz.  A current-loop natural frequency of 200 Hz with a damping ratio of 0.7 is desired.  The PWM-
max-count variable is at the default value of 6528, and Ixx66 for the motor is at the recommended value 
of 7181 (10% greater). 

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Preparation for Experimental Tuning 

Typically the experimental current-loop tuning is done through the Turbo Setup program or the PMAC 
Executive program; both create the proper setup for the tests automatically.  However, to do the test 
manually, follow the instructions in this section. 
To prepare Turbo PMAC for this test: 

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Set Ixx00 for all other motors to 0 to de-activate them. 

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Set Ixx01 for all other motors to 0 to turn off the commutation.  This makes sure Turbo PMAC has 
enough calculation time to gather data fast enough. 

• 

Set I7m02 to 0 for divide-by-1 to make servo update rate equal to phase update rate.  This permits 
Turbo PMAC to gather data every phase update.) 

To set up the motor under test: 

• 

Set Ixx00 to 1 for the motor under test to activate it. 

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Set Ixx01 to 1 for the motor under test to turn on phase/current calculations.  These may have been 
left at zero from the earlier tests. 

• 

Give the motor a K command to turn off the outputs 

• 

Set Ixx71 to 1 to cripple the commutation algorithm and prevent movement during the test. 

• 

Make sure the other setup I-variables are set as instructed above.  I7m02 and Ixx71 only should be 
different from what they would be in the final application. 

• 

Start with Ixx62=0.1, Ixx61=0.0, and Ixx76=0.0 as current loop gains. 

• 

Set Ixx77 to 3000 to provide about 10% direct current command.