July 2013 7.4 Single-speed, double-speed, PWM frequency 1085
The optimum switching speed results from the intersection of the maximum
current curve of the motor with the maximum current curve of the power
module for the high PWM frequency. You can determine the maximum
current curve of the spindle motor by using the TNCscopeNT software.
Record the current Inoml/S in dependency of the speed. The spindle must be
accelerated to the maximum speed so that the derating behavior can be seen
in the curve. The figure shows the behavior when the values entered for the
switching speed (MP2186.x, MP2188.x) are too low. This then results in a
speed range where the current for the motor is less than the permitted and
maximum current, resulting in inconsistencies in the motor’s torque behavior.
1: Red line: Maximum current for the drive, resulting from the entries in
MP2186.x and MP2188.x
1: Broken line:
Maximum possible current for the drive (Imax of motor)
2: Switching point for the PWM frequency set too low
3: Optimum switching point for the PWM frequency
4: Maximum power-module current at low PWM frequency
5: Maximum power-module current at high PWM frequency
(Imax of power module)
Please note that switching the PWM frequency always influences both PWM
outputs of a drive-control board. Switching a single PWM output is not
possible. This means that only one of the two outputs can be used. Besides,
a PWM output with a PWM frequency > 5 kHz requires increased
performance as well as software option 49, see page 1074.
To Next Page
Loading...
