Re: stepper reluctance

Thanks to Mariss & Michael for their input.

Regards

Bob Thomas


-- In CAD_CAM_EDM_DRO@y..., "mariss92705" <mariss92705@y...> wrote:

> Bob,
>
> I think you are confusing apples with oranges here. A high frequency
> switching drive simply regulates motor phase current at low to
> moderate speeds. As speed increases, so does inductive reactance
> until it becomes large enough to limit motor current. At that point a
> switching drive ceases switching and simply applies the full power
> supply voltage across the winding for the entire period, (2 full
> steps).
>
> The switching algorithm goes like this:
>
> (1) Apply full voltage to the winding. Current builds up at the rate
> of Volts / henries (V/L) amps per second.
>
> (2) Has the current built up to the command reference value? If no,
> repeat (1) and (2); if yes, goto (3)
>
> (3) Apply reverse voltage on the motor. Current now decays at a V/L
> rate.
>
> (4) Has the switching time period expired (typically 20 to 25uS)? If
> no, repeat (3) and (4); if yes, goto (1).
>
> As you can see, at high speeds you would never get to (3) and (4)
> before it was time to reverse current in the winding because the step
> sequence demands it.
>
> There is no down side to it. The up side is a tremendous heat saving
> at low speeds when compared to a linear amplifier drive.
>
> Mariss
>
>
>
> --- In CAD_CAM_EDM_DRO@y..., "echnidna" <echnidna@y...> wrote:
> > Hi group,
> > given that motor reluctance governs maximum motor speed.
> > what is the advantage of chopper drive at high frequency which
> means higher impedance?
> > wouldnt a simple linear current control be more effective by
> avoiding very high chopper frequencies?
> >
> > Regards
> > bob Thomas