Reference Manual

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Turbo PMAC/PMAC2 Software Reference

Turbo PMAC Global I-Variables 134

Ixx76 Motor xx Current-Loop Back-Path Proportional Gain

Range: 0.0 – 2.0 (24-bit resolution)

Units: PWMout = -4 * Ixx62 * (Iact)

Default: 0.0

Ixx76 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 Ixx76 or

Ixx62 (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 Ixx76 is used as the only proportional gain term, only the Ixx61 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, Ixx76 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.

Ixx76 is typically set using the current loop auto-tuner or interactive tuner in the Turbo PMAC Executive

Program. Typical values of Ixx76, when used, are around 0.9.

Digital current loop closure on the Turbo PMAC requires a set of three consecutive command output

registers. Generally, this requires writing to either a PMAC2-style Servo IC or a MACRO IC.

Ixx76 is only used if Ixx82>0 to activate digital current loop execution.

Ixx77 Motor xx Magnetization Current

Range: -32,768 – 32,767

Units: Bits of a 16-bit DAC

Default: 0

This parameter 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 generally be set to zero for non-induction motors,

unless advanced “field weakening” algorithms are desired.

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 Commutation section of the manual for instructions in optimizing the

setting of this parameter. The Turbo Setup expert-system program for PCs is typically used to set the

proper value of Ixx77 for induction motors.

If Ixx77 is set to a non-zero value, Ixx69 should be reduced from what it would be with Ixx77 set to 0.

The effective current limit is:

77Ixx

69Ixx

max

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