The philosophy of the 6, 12, etc. pulse rectifier or battery charger is based on the fact that the higher the number of pulses, the lower the input current harmonics, the higher the input power factor, and the lower the output voltage ripple.
The topology of these two models of a rectifier or thyristor battery charger has two basic differences:
a) The number of thyristors in 6 pulses, is 6, and in 12 pulses, is12.
b) The type of transformer that has a 3-phase output in a 6-pulse transformer and a 6-phase output in a 12-pulse transformer.
In the case that the rectifier or thyristor  batterycharger has 12 or more pulses, they are made in the form of  6 pulses module, which can be connected in parallel or in series.