>As it turns out, I'm told the frequency of interest from the turbine
>is > 450Hz, and switch-over frequency (star-delta) is ~ 650Hz,
...
>Now I'm trying to help him with the rectification.

You may need to look at recovery time of the rectifiers at that sort of 
frequency. I know older 1N400x series diodes have visible reverse recovery 
time on an oscilloscope at 50Hz, so it is probably worth at least checking 
the RRT rating on whatever you choose, otherwise your diodes may become a 
significant heat loss point affecting the overall efficiency.

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