areobat:
I think the +/- 270 VDC buss is rectified, but un-filtered DC, probably
3 wire, bipolar buss derived from a Wye connected gen-set/rectifier.
This would have a pseudo AC appearance on a scope. The cost/weight
penalty to condition this high power buss would be huge and is really
not necessary for driving large motor loads. PWM VFDs are more than
capable of dealing with a "dirty" input and large motors are more than
happy to run on a dirty output. A bipolar input would reduce the parts
count for the VFDs as well.
Thanks for that. From what I remember, 3 phase rectified output looks
like dc with superimposed ripple on top. As you say, it would be fine
for input to a VFD and the bipolar configuration would reduce parts
count elsewhere. Could also cancel any magnetic fields that could affect
things like magnetic compasses, assuming the +/- were tracked together
in the loom.
One thing that is interesting to me is that all six AC gen sets appear
to be paralleled. Phasing gen sets on separate shafts can be a real
pain. It would interesting to see how that is handled.
I guess initially, the shaft speed control must be pretty close. Then
when online, they would tend to lock to each other, just as with the
generators in the national grid. For each shaft, power output is varied
by by fine adjustment of fuel and generator exitation, via some smart
electronics. If you've done this stuff before, correct me if i'm wrong
there.
Wind Generators: With such low blade speeds, do they use step up gearboxes
to get the correct speed for the alternator, viscous couplings etc and how
is it connected to the grid ?. Direct connection as an induction generator,
or via an inverter ?. Off topic, sorry, but just curious...