Jinx wrote:
> My contact spent all day at Auckland Uni's wind tunnel. The result
> is that, as known previously, even if the propellors could be got going
> at low rpm, the power output is almost unusably low compared with
> star
> 
> At 120 rpm, delta = 11.8V @ < 0.5A and star = 11.8V @ 9A. Power
> production in delta configuration doesn't really kick in until about 300
> rpm. If you can live with 20A max output, then the generator can be
> left in star configuration. The problem is that the commercial competition
> use the higher delta output (35A) in the upper rpm range as a selling
> point, even though the prevailing wind conditions are at the low end,
> where star is more efficient, and moderate winds where star and delta
> are comparable
> 
> To compete with others' claims, star-delta switching is unavoidable

This is getting a bit tedious, and you are completely refusing to "think
outside the box" on this one.

The point that others have been trying to make is that with modern
swtiching regulators -- boost/PFC in particular -- you can completely
control the rate at which you extract power from the generator.

The problem with delta configuration at low RPM is that the maximum power
is available at a voltage lower than your battery bus. This problem is
easily fixed with a straightforward boost regulator. It even has the
advantage of simplicity -- as the RPM and generator voltage rises, the
boost regulator will automatically stop operating and the current will
flow directly through the regulator's coil and diode to the battery bus.

If you are considering star-delta switching at all, you clearly have
access to all six leads (three isolated sets of coils) coming out of the
generator. If you really want the best efficiency at all speeds, here's the
leap you need to make: Don't hook them together at all! Instead, connect
each one to an H-bridge, controlled in such a way to both full-wave rectify
it and to develop a PFC behavior using the inductance of the generator coil
itself. This allows you to directly control the load impedance that the
generator sees. Connect the three PFC outputs to your battery/inverter bus.

You will be able to extract the maximum available power at all speeds, and
there will be no cogging/startup issues at all, because the electrical
load that the generator sees will be purely resistive. Reliable technology
to accomplish this should be readily available, because this is precisely
how regenerative braking in electric/hybrid vehicles works.

-- Dave Tweed
-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist