Re: [CAD_CAM_EDM_DRO] Re: Microstepping thru the Tulips

Phil Mattison wrote:

>Perhaps, but a 100KHz microstep rate and a 20KHz PWM frequency implies that
>the coil current is modified five times in a single cycle of the PWM, which
>is absurd. In that case, the PWM (or chopper, whatever) cannot produce the
>power modulation that is supposed to be the big deal with microstepping. Any
>microstep rate above the PWM frequency renders it meaningless. What you end
>up with in practice is a single-step driver.
>
>

100KHz into a Gecko 201-series drive is 10,000 full steps per second
(10X microstepping).
With a 200 full-step/rev motor, that is 50 revs/second, or 3000 RPM. Do
you really intend
to run stepper motors at this speed? I have run steppers with a Gecko
201A drive up
to 1440 RPM, and that was sure enough for me. At these speeds, the
inductance of the
motor winding is a HUGE factor, and I believe the motor current may
approach a pure
sinusoid because the drive will use a 100% PWM duty cycle as it attempts
to drive
rated current through the windings. If not, the current will be linear
ramps that never
reach rated current before the transistors switch to the next phase
polarity. The back-
EMF becomes pretty dominant at these speeds, and the phase shift between
voltage and
current complicates the equation.

Jon