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Registered Member #599
Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 624
I cant wrap my head around this problem right now:
3x400VAC 3 phase results 565VDC when rectified with 6-pulse rectifier. But how about if i use three single phase voltage doublers and parallel their outputs, would that work? All three doublers would have common neutral wire. Voltage between L1/L2/L3 - N is 230Vrms and 400V between phases because of 120degree phase shift.
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
Perhaps it's easier to think of what you've drawn as 3 half-wave rectifiers to the +ve output, generating +340v peak with 3 pulses per cycle, and the inverse to the -ve output. The +ve pulses and -ve pulses will interleave, so giving 300Hz ripple to the total 680v differential voltage, rather than the 150Hz ripple on each 340v with respect to N. f you're having difficulty seeing that, just delete all the C2/D2 components and analyse what's left.
Registered Member #2529
Joined: Thu Dec 10 2009, 02:43AM
Location:
Posts: 600
Without checking your circuit it is certainly possible to get higher DC voltages from diodes and capacitors and AC, that's how a Cockcroft walton works:
Registered Member #599
Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 624
I tried my best with LTspice and could not get the above circuit working at all. It either takes days to simulate or I get something like nanovolts and pico amps out :)
Its more than likely something I did wrong but I cant figure out what
EDIT: Wohoo got it working! Spice simulators are weird sometimes :)
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
The diagram is correct but a more common method is to not use the Neutral connection, exactly as your diagram but with all wires to Neutral removed. You will need 'balancing' resistors across the capacitors, a little inefficiency but the cap bank will be discharged quickly for servicing/experimenting etc. The reason for NOT using the Neutral is to avoid RCD trips.
You should use some kind of 'inrush' protection (protect against huge currents charging the cap bank from 0v to max. at switch on) A resistor that can be shunted by a relay contact, triac etc. once the cap bank is at c90% voltage.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
It will work but the neutral connection will see high current pulses at the 150 Hz ripple frequency. This will result in increased heating of the Neutral conductor and increased skin effect in it, which all mean unnecesarry additional losses. That is why you always try to avoid Neutral current in three phase loads.
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650VDC from 3x400VAC 3 phase
