Reference Manual

Turbo PMAC/PMAC2 Software Reference
Turbo PMAC Global I-Variables 120
Ixx56 Motor xx Commutation Delay Compensation
Range: 0.0 – 1.0
Units: (Ixx09*32/2048) commutation cycles/(counts/servo update)
Default: 0
Ixx56 permits the Turbo PMAC to compensate lags in the electrical circuits of the motor phases, and/or
for calculation delays in the commutation of Motor xx, therefore improving high-velocity performance.
The compensation is simply Ixx56 multiplied by the motor velocity.
Ixx56 is only used if Turbo PMAC is commutating Motor xx (Ixx01=1). It should be only be used for the
commutation of synchronous motors (Ixx78=0) such as permanent magnet brushless motors. Ixx56
should be set to 0 for asynchronous motors (Ixx78>0) such as AC induction motors.
If Turbo PMAC is commutating Motor xx, but not closing the current loop (Ixx82=0), Ixx56 can improve
performance typically starting at a few thousand RPM, because it compensates for inductive lags in the
motor windings. If Turbo PMAC is also closing the current loop for Motor xx (Ixx82>0; Turbo PMAC2
only), the DC field-frame current loop closure compensates for inductive lags, and only small calculation
delays need to be compensated; these are usually not significant until well over 10,000 rpm.
This parameter is best set experimentally by running the motor at high speeds, and finding the setting that
minimizes the current draw of the motor.
Example
On a 4-pole motor with a 512-line encoder and “times-4” decode, it is desired to have an advance of 5
degrees (electrical) at a motor speed of 30,000 rpm. The Ixx56 advance gain converts from speed,
expressed in (1/[Ixx08*32]) counts per servo cycle, to advance, expressed in (1/2048) commutation
cycles.
First convert our speed to these units:
 
ct
ctsIxx
rev
cts
sservocycle
rev ]32*08/[132*96
*
2048
*
2260
sec
*
sec60
min
*
min
000,30
servocycle
ctsIxx ]32*08/[1
616,391,1
Next, convert our desired advance to these units:
)2048/1(44.28
360
)2048/1(2048
*5 commcycle
e
commcycle
e
o
o

Finally, compute Ixx56 as the ratio of advance to speed:
0000204.0
616,391,1
44.28
56 Ixx
Ixx57 Motor xx Continuous Current Limit
Range: -32,768 – 32,767
Units: 16-bit DAC/ADC bit equivalent
Default: 0
Ixx57 sets the magnitude of the maximum continuous current limit for Turbo PMAC’s integrated current
limiting function, when that function is active (Ixx58 must be greater than 0 for the integrated current
limit to be active). If Turbo PMAC is closing a digital current loop for the motor, it uses actual current
measurements for this function; otherwise, it uses commanded current values. If the magnitude of the