> The 'easy' way to make a sine converter is to use a class B push-pull
> amplifier and a split secondary transformer (2x10V for 12V batteries).

Not so easy when you realize that class B is not very efficient, and at
his power levels getting rid of the heat will be a significant challenge.

Commercial inverters either alternately drive the transformer primary to
full in each direction producing a sort of rounded square wave, or they
use DC-DC converter techniques to drive the primary with a high frequency
chopped sine wave as you said.  The rounded square wave approach may not
be as bad as it first appears, depending on the loads you plan on driving.
Incandescent light bulbs and electronic equipment with switching power
supplies (like a PC) don't mind this at all.  However, sine wave output is
the only thing guaranteed to work with all standard appliances.

> All
> the other ways involve a DC/DC converter steered with |sin| waveform and
> an active H bridge in the high voltage side.

Really, "all" other configurations than class B are like this!?  C'mon
now.  For one thing, you can use the same center tapped primary you
mentioned above, center to the +DC supply, and each end switched to ground
using PWM so as to produce a sine wave out.  In fact, it was my
understanding that this was a reasonably common arrangement.

> This will give about 70% efficiency, which is low.

A well tuned and tweaked system should be able to do better than 70%, but
that is still a lot better then class B.

> Maybe it would be easier to convert the 115Vac
> installation to 24Vdc or 48Vdc and save one major part (or pita). What
> would it take to convert the blower to a static switched dc motor ?
These
> are made to specs like you need for servo purposes.

That may be a reasonable approach in some cases, but I think the original
poster is doing this partly for the sake of doing and learning this
himself.  Certainly a system that produced normal line power would be much
more flexible, and a much better learning experience.


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