User's Manual

Turbo PMAC User Manual
Setting Up Turbo PMAC-Based Commutation and/or Current Loop 127
Finishing Setting up Turbo PMAC Commutation (Direct PWM or Sine
Wave), Asynchronous (Induction) Motors
Turbo PMAC commutation of an AC induction motor requires the setup of two I-variables that can be left
at 0 for permanent-magnet brushless motors. One variable is the Ixx77 magnetization-current parameter
(which is usually left at 0 for permanent-magnet motors, but can be changed for them). The other
variable is the Ixx78 slip-gain parameter (which must be left at 0 for permanent-magnet motors).
Typically, the Turbo Setup program can be used to set Ixx77 and Ixx78 automatically. The program
stimulates the induction motor to infer its parameters, and sets these terms appropriately for the results it
gets. This section explains analytical and experimental methods for setting these parameters. These settings
are independent of any mechanical load, so any tests can and should be done with an unloaded motor.
Calculating Ixx78 Slip Constant
Calculating from Name Plate Data
The slip constant parameter Ixx78 for an induction motor can be calculated simply from basic parameters
for the motor and for the Turbo PMAC. The following is needed:
• The rated speed for the motor, usually given in revolutions per minute (rpm).
• The electrical line frequency given for this rated speed, usually given in Hertz (Hz), or cycles/sec.
• The number of poles for the motor.
• The Turbo PMAC’s phase update period, usually given in microseconds (µs).
The rated speed can be subtracted from the line frequency (after conversion to consistent units) to get the
slip frequency. This can be multiplied by the phase update period (again after conversion to consistent
units) to get the Ixx78 slip constant. The formula is:
()
768,32
std_mag
I
*
p
T*
me
78Ixx
ωω −=
where:
ω
e
is the electrical frequency given, in radians/sec. To calculate from frequency in Hertz, multiply by 2π
(6.283).
ω
m
is the rated mechanical pole frequency, in radians/sec. To calculate from motor rated speed in rpm
and the number of poles, divide the speed in rpm by 60, multiply by 2π (6.283), then multiply by the
number of poles and divide by 2.
T
p
is the Turbo PMAC’s phase update time in seconds. To convert from microseconds, divide by one
million. For a Turbo PMAC2, the phase update time can be calculated as:
(
)
[]
(
)
[
]
11796480
1619II*3719II*2
p
T
+−+−
=
where I19 is the Turbo PMAC2 parameter containing the number of the clock direction I-variable for the
Servo IC or MACRO IC that is the source of the phase and servo clocks for the system. Usually I19 is set
to 6807 for a Turbo PMAC2 Ultralite to specify MACRO IC 0 (so I6800 and I6801 set the phase update);
usually it is set to 7007 for a board-level Turbo PMAC2 to specify Servo IC 0 (so I7000 and I7001 set the
phase update); usually it is set to 7207 for a UMAC Turbo to specify Servo IC 2 (so I7200 and I7201 set
the phase update).
I
mag_std
is the value of the magnetization current parameter Ixx77 that would produce the same rated
speed/torque point as the direct operation off the AC lines. For a first calculation, use a value of 3500
here. Usually, it is close enough. If the value of Ixx77 is set as explained in the next section for this type
of operation, come back and adjust this calculation.