----- Original Message -----
From: Andrew Kunz <akunz@TDIPOWER.COM>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Monday, August 21, 2000 2:53 PM
Subject: Re: [PIC]: Sine table


> >You're correct. I was assuming that you had continuous access to the sine
wave.
>
> That would be too easy.
>
> >I guess it's safe to assume then that the `off-chip electronics' do some
kind
> of
> >conditioning to guard against the noise problems I alluded to before. I
haven't
>
> I would hope so.  They haven't finished a spec yet, but that's an item I
can
> write in.
>
> >variation], otherwise there will be jitter if N doesn't exactly divide
into
> >period of the sine wave).
>
> My plan was to accumulate the error and every M steps insert/delete a uS
or so.
> My goal is to hit 0V within 6 uS of the mains.
>
> >What does the synthesized sine wave need to lock to?
>
> Incoming power from the electric company 3-phase setup.  I will only use
one
> phase as my master reference, the other is assumed to be 90 degrees off.

Huh? 90 degrees?

Aren't the phases in 3-phase 120 degrees apart?

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)s

>
> >Is it sufficient to generate the right frequency?
>
> Yes, but be locked to the source for phase.  It's for continuous UPS
equipment.
> I have to generate the sine waves, and lock to the incoming frequency off
the
> mains.  The frequency may change slowly but will nominally be either 50 or
60
> Hz.  My portion is simply to lock to the incoming wave, generate the sine
waves
> (on a parallel DAC), and if the input goes away I just lock to the last
> reasonable frequency.  When line power comes back on, I will need to lock
to it
> and once locked, flip a switch to enable the mains to provide power again
(mains
> are locked out after a failure).
>
> My other input is "phase present" for each phase of the input power.  If
mains
> are not present at startup, I default to the last nominal frequency
(either 50
> or 60 Hz).  That is not necessarily the last frequency I saw due to the
way
> lines go dead.
>
> The trickiest part of the whole thing will be that I will be crossing 0 at
a
> different time the the inputs, because there is a lag time in the power
> electronics vs. the sine wave I am feeding them.
>
> Andy
>
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