Reference Manual

PMAC 2 Software Reference
PMAC I-Variable Specification 107
Ix76 Motor x Velocity Phase Advance Gain {PMAC(1) Only}
Range
0 .. 8,388,607
Units
(Ix09*32) / (Ix70*2
23
) counts / (counts per servo update)
Default
0
Remarks
Ix76 advances the phasing angles on a motor commutated by PMAC(1) by an amount
proportional to the measured velocity of the motor. This compensates for the lag in the
electrical circuits of the phases, and for calculation delays. It should be set to zero for
induction motors.
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.
See Also
Setting Up PMAC Commutation
I-variables Ix70-Ix75
Ix76 Motor x Current-Loop Proportional Gain (Back Path) {PMAC2 only}
Range
0.0 .. 1.0 (24-bit resolution)
Units
PWMout = -4 * Ix76 * (Iact)
Default
0.0
Remarks
Ix76 is the proportional gain term of the digital current loop that is in the back path of the
loop, multiplying the actual current level, and subtracting the result from the command
output. Either Ix76 or Ix62 (forward path proportional gain) must be used to close the
current loop. Generally, only one of these proportional gain terms is used, although both
can be.
If Ix76 is used as the only proportional gain term, only the Ix61 integral gain term reacts
directly to command changes. The act of integration acts as a low-pass filter on the
command, which eliminates a lot of noise, but lowers the responsiveness to real changes.
Generally Ix76 is only used when the command value from the position/velocity loop
servo have high noise levels (usually due to low position resolution), and the actual current
measurements have low noise levels.
Typically, Ix76 is set using the current loop auto-tuner or interactive tuner in the PMAC
Executive Program. Typical values of Ix76, when used, are around 0.5.
Ix76 is only used if Ix82>0 to activate digital current loop execution.
See Also
Setting Up PMAC Commutation
I-variables Ix61, Ix62, Ix66, Ix82
Ix77 Motor x Induction Motor Magnetization Current
Range
-32,768 .. 32,767
Units
DAC bits
Default
0
Remarks
Ix77 is used in induction motors to provide a stator current component parallel to the
estimated rotor magnetic field (the “direct” current – the control loop determines the
magnitude of the “quadrature” current perpendicular to this component). This should be
set to zero for non-induction motors. The proper value for an induction motor is system
dependent, but 2500 is a good starting value for most motors. Refer to the Setting Up
PMAC Commutation section of the manual for instructions in optimizing the setting of this
parameter.
See Also
Setting Induction Motor Parameters (Setting Up PMAC Commutation)
I-variables Ix01, Ix70-Ix72, Ix78