Re: DC Motor Control: H-Bridge +5A, 48v

In article <5nea81da4dsamb5n7i9nligl6rptgkah5c@xxxxxxx>,
cdsmith69NOSPAM@xxxxxxxxxxxxx says...
> On Fri, 13 May 2005 14:44:37 -0400, R Adsett
> <radsett@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> >In article <lfd281hl7ib4d2b07t7q3nt7kk5n5hl9eu@xxxxxxx>,
> >cdsmith69NOSPAM@xxxxxxxxxxxxx says...
> >>
> >> When we would run the lift motor at about half PWM, which
> >> resulted in maybe 250 amps or so, the image on the CRT of that
> >> old WYSE terminal would shake up and down about 1/4 inch, even
> >> though it was on a table a couple feet away.
> >
> >Seen that too. It sounds like we had similar experiences at roughly the
> >same time. Any chance your lift truck was a reach? :)
>
> Nope. Just a stand up counterbalance.
>
>
> >Speaking of current limits. The controller was designed, over my
> >objections, to use the NMI to signal an over-current.
>
> Already sounds bad...

Once I managed to get the NMI down to something like three instructions
it worked rather well. It all depends on latency, how close you are to
the end of the pwm cycle when you hit current limit and the motor
inductance. It worked for all but the most degenerate cases.
Nonetheless capping the maximum repeat rate was a definite improvement.

<snip>

> Later we were designing a new controller that did cycle by cycle
> current limiting. That worked so much better there was no
> comparison. It would just take the controller to maximum power
> and sit there. You could even slam the PWM on to 100% and just
> watch each cycle current limit a little later as the motor sped

Saw a controller (I did the production test benches for it) that used
that for an inner current loop. Quite effective.

I did software current control on multiple bridges in a single micro to
do similar control. Once it's tuned it's very effective. You do have to
be careful while tuning though.

We did run into an issue with plugging. It turns out that under certain
circumstances once you start plugging it will self sustain and the only
way to get it to stop braking is to open the direction contactors. The
motors we first tested on actually braked very nicely in that mode.

> up. But that design never made it to production, as it was in
> progress at the time of the Great Downsizing that left the
> company with 1 employee.

Ouch.


Robert
.

Relevant Pages

  • Re: What passes as Pulse Width Modulation in DC Motor Control?
    ... Assuming a PWM 50% duty cycle, ... We have an ideal motor (i.e. no resistance losses, ... etc.) which is being driven by an ideal PWM. ... with our ideal motor and ideal PWM, then the power from the 20 volts ...
    (sci.electronics.basics)
  • Re: What passes as Pulse Width Modulation in DC Motor Control?
    ... Assuming a PWM 50% duty cycle, ... We have an ideal motor (i.e. no resistance losses, ... etc.) which is being driven by an ideal PWM. ... the PWM is switching the motor drive between 20 volts and 0 volts. ...
    (sci.electronics.basics)
  • Re: What passes as Pulse Width Modulation in DC Motor Control?
    ... Assuming a PWM 50% duty cycle, ... We have an ideal motor (i.e. no resistance losses, ... etc.) which is being driven by an ideal PWM. ... the PWM is switching the motor drive between 20 volts and 0 volts. ...
    (sci.electronics.basics)
  • Re: What passes as Pulse Width Modulation in DC Motor Control?
    ... Assuming a PWM 50% duty cycle, ... We have an ideal motor (i.e. no resistance losses, ... etc.) which is being driven by an ideal PWM. ... with our ideal motor and ideal PWM, then the power from the 20 volts power ...
    (sci.electronics.basics)
  • Re: DC Motor Control: H-Bridge +5A, 48v
    ... The controller was designed, over my ... overcurrent was tripping. ... the next PWM cycle after the one-shot. ... Later we were designing a new controller that did cycle by cycle ...
    (sci.electronics.design)