For very high-power rectifiers the 24-pulse bridge connection is used. A 24-pulse bridge consists of four six-pulse bridge circuits connected in series or parallel, with their AC connections fed from a supply transformer that produces a 15° phase shift between the two bridges. This cancels many of the characteristic harmonics the six-pulse, twelve-pulse and 18-pulse bridges produce and as a result the input current waveform it's much more sinusoidal.
Also note that that the ripple in the DC side is significant small.
In the example every three phase source represents one of the four secondary windings of the supply transformer.
http://www.scielo.org.co/img/revistas/iei/v31sup2/v31sup2a19f6.jpg
http://www.joliettech.com/images/abb_line-current-harmonics.gif
