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Turbo PMAC/PMAC2 Software Reference

Turbo PMAC Global I-Variables 132

If Ixx80 is 2 or 3, the “stepper-motor” phasing search is used, and Ixx73 controls the magnitude of current

forced into individual phases to lock the motor to a position like a stepper motor. In this method, if the

Turbo PMAC is not performing current loop closure for the motor (Ixx82=0) and Ixx72 > 1024, then

Ixx73 should be set to a negative number of the desired magnitude. In all other cases it should be set to a

positive number. If the sign of Ixx73 is wrong for a setup, the motor will run away when the loop is

closed.

A negative value of Ixx73 must be used for sinewave-output commutation (Ixx82 = 0) with Ixx72 > 1024

and the stepper-motor phase search method (Ixx80 bit 0 = 1).

Typically, values of magnitude 2000 to 6000 are used for Ixx73 in either method.

See Also:

Power-Up Phasing Search (Setting Up PMAC Commutation)

I-Variables Ixx01, Ixx74, Ixx78, Ixx80, Ixx81

Ixx74 Motor xx Phase Finding Time

Range: 0 – 255

Units: Servo Interrupt Cycles (for Ixx80 = 0 or 1)

Servo Interrupt Cycles * 256 (for Ixx80 = 2 or 3)

Default: 0

WARNING

An unreliable phasing search method can lead to a runaway condition. Test the

phasing search method carefully to make sure it works properly under all

conceivable conditions. Make sure the Ixx11 fatal following error limit is active

and as tight as possible so the motor will be killed quickly in the event of a serious

phasing search error.

Ixx74 defines the time that an open-loop output is to be used if a power-on phasing search is done for a

PMAC-commutated motor (Ixx01 bit 0 = 1). A phasing search is required for a synchronous motor

(Ixx78=0) such as a permanent-magnet brushless motor with no absolute position sensor (Ixx81=0). The

phasing search is done automatically as part of the power-on phasing search if bit 0 of Ixx80 is 1; if bit 0

of Ixx80 is 0, the on-line $ or $$ command must be used must be used to initiate the phasing search.

If Ixx74 is set to 0, no phasing search move will be done, even if one is requested and required. In this

case, the “phase reference error” motor status bit will stay set, preventing the servo loop from closing.

If bit 1 of Ixx80 is 0 (Ixx80 = 0 or 1), the two-guess phasing search is used; Ixx74 has units of servo

cycles and controls the time for the open-loop command at each “guess” of the phase angle. Typical

values are three to ten servo cycles; a value of 5 is a good starting point.

If bit 1 of Ixx80 is 1 (Ixx80 = 2 or 3), the stepper-motor phasing search is used; Ixx74 has units of (servo

cycles*256) and controls the time current is forced into each phase and Turbo PMAC waits for the motor

to settle into the step position. With the default servo cycle rate of 2.25 kHz, each unit of Ixx74

represents about 0.1 seconds in this mode; typical values are 10 to 20.