-=> Quoting Roy McNeill to John Tserkezis <=-

Hello Roy,

 JT> The way they usually do it, is convert the incoming DC to 340v, and
 JT> use a push-pull arrangement with PWM to simulate a sine wave. Then
 JT> filter it anyway, using more or less standard mains filters. You
 JT> will get a small amount of switching noise in the mains, but it
 JT> mostly depends on how quick the PWM was.

 RM> I see, a two stage arrangement. Stage 1 is a regulated dc-dc
 RM> converter running at some random freq, optimized for efficiency,
 RM> and stage 2 is a transformerless switching array with no regulation
 RM> but tight control of switching times.

 It output is actually regulated, but feedback is returned to the first stage.

 RM> I'll add it to the list, but it's a bit too complex for the job I
 RM> have in mind. A vaguely filtered squarewave should do the job.

 There are many similar arrangements, that only have a simple square wave
output in the second stage.  Generally, the above method is used for the
higher power inverters.
 The second square wave type I mentioned is sometimes called a "modified square
wave inverter" although the ones I've seen are quite crude.

 The second stage switches like this:

     ----      ----
     |  |      |  |
    -|  |-|  |-|  |-
          |  |
          ----

 So much for "modified square wave".

 RM> The choo choo inverters, btw, use method 1, but their main
 RM> purpose in life is to drive motors.

 You mean the PWM type?  The fancy nancy train controllers do yes.  The
simpler ones just use a high power variable resistor in series. (Bodgie yes,
but cheap).

 As I had missed the original message, I was going to ask what your use was
when I remembered I may as well have a look in my own message base.  I still
can't work out exactly what you are after.
 So far, I can tell you want a fairly efficient inverter to go from battery
power to mains, and probably three phase as well.

 What type of load will you be using, and how much of a load will it be?
Another option is for you to do the pwm switching at the battery voltage side,
and use a standard mains transformer to step it up to 240.  Although if you
want to use it with proper PWM and simulate a sine wave, you will have to do
some real processor work as far as regulation goes.  I see you have used a PIC
to go up to 1.something KHz so far, I don't know if that was a proper
simulated sine wave, or just plain square wave.  One PWM inverter I've seen,
fairly high power (around 2KW) used an eprom to generate the PWM signal on
the mains 340V dc side.

 If it is just a square wave, you don't really need a PIC, as it can be done
cheaper with garden variety components.  I think EA had a simple low power
(40VA) 12 inverter that used this principal.

John Tserkezis, Sydney, Oz. Fidonet: 3:712/610  Internet: jt{at}suburbia.com.au

... Atheist having an orgasm: "Oh, Random! Oh, Chance!"
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