Re: [CAD_CAM_EDM_DRO] 3 phase steppers (was: Motor current measurement)

Jon Elson wrote:

> speeds, a 6-step drive
> will probably suffice. If you want the ultimate performance, then
> sine-wave drive will do
> just a little better. (The same is completely true for 2-phase
> steppers, too.)
>
> With a PWM amp, you CAN, indeed, feed sine wave currents to the
> windings, setting the PWM
> duty cycle to obtain the average current desired. This is exactly how a
> 2-phase microstepping drive
> works. It is also how some VFDs work, although many of these are
> programmed to produce 3-phase
> voltages, not currents.

Hi Jon,

yes, sounds reasonable. But what strategy is used to regulate the
current? For a 2 phase drive it's easy because the windings have
separate terminals. You can simply turn on the corresponding transistor
and wait for the current to rise to the nominal level and then turn off.

At a 3 phase drive I could do the same for 2 terminals but the current
of the 3rd is always the sum of the 2 others. So depending on the angle
of the current vector I have to consider which terminals are regulated
and which is "floating" and have to switch the current sensor inputs
accordingly. Sound a bit tricky to me. I thought there is some trick to
simplify this.

Ciao
Bene

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