Reference Manual

Turbo PMAC/PMAC2 Software Reference

Turbo PMAC Global I-Variables 129

 The amplifier has the lower instantaneous current rating, so we use its limit of 25 amps (RMS).

 25 amps (RMS) corresponds to peak phase currents of 25*1.414 = 35.35 amps.

 I769 is set to 32,768 * 35.35/40 = 28,958.

5. Motor 9 is driving a direct-PWM power-block amplifier and an AC induction motor. The Ixx77

magnetization current parameter is set to 3000. The A/D converters in the amplifier are scaled so that

a maximum reading corresponds to 100 amps of current in the phase. The amplifier has an

instantaneous current limit of 60 amps (RMS), and the motor has an instantaneous current limit of 75

amps (RMS).

 PMAC’s maximum ADC phase reading of 32,768 corresponds to 100 amps in the phase.

 The amplifier has the lower instantaneous current rating, so we use its limit of 60 amps (RMS).

 60 amps (RMS) corresponds to peak phase currents of 60*1.414 = 84.84 amps.

 84.84 amps corresponds to an ADC reading of 32,768 * 84.84/100 = 27,800.

 The vector sum of Ixx69 and Ixx77 should equal 27,800 * 0.866 = 24,075.

 I969 should be set to sqrt(24,075

-3,000

) = 23,887.

Motor Commutation Setup I-Variables

Ixx70 Motor xx Number of Commutation Cycles (N)

Range: 0 – 255

Units: Commutation Cycles

Default: 1

For a PMAC-commutated motor (Ixx01=1), Ixx70 is used in combination with Ixx71 to define the size of

the commutation cycle, as Ixx71/Ixx70 counts. Usually, Ixx70 is set to one, and Ixx71 represents the

number of counts in a single commutation cycle. However, many people will use Ixx70 to represent the

number of commutation cycles (pole pairs) per mechanical revolution, and Ixx71 to represent the counts

per mechanical revolution. Ixx70 needs to be set greater than one if the number of counts in a single

cycle is not an integer.

A commutation cycle, or electrical cycle, consists of two poles (one pole pair) of a multiphase motor.

Setting Ixx70 to 0 effectively defeats the creation of the AC commutation cycle. This setting can be

useful when doing direct PWM control of DC brush motors which requires the use of the Turbo PMAC

commutation algorithms, but cannot use an AC output.

Example:

A 6-pole brushless motor has three commutation cycles per mechanical revolution. If a feedback device

with 4096 counts per mechanical revolution (a number not divisible by three) is used, Ixx70 should be set

to 3, and Ixx71 to 4096.