Power conversion circuits

An alternating current (AC) power conversion system, comprising:

• at least two AC power converter circuits for coupling respective loads in parallel to a multi-phase AC power supply, each AC power converter circuit including a plurality of rectifiers for passing respective phases of the AC power supply in turn at respective firing angles, wherein a first of the AC power converter circuit includes a first positive group of rectifiers and a first negative group of rectifiers, and wherein a second of the AC power converter circuit includes a second positive group of rectifiers and a second negative group of rectifiers;
• a controller coupled to the at least two AC power converter circuits for symmetrically controlling the rectifiers of the at least two AC power converter circuits, such that the firing angles for the at least two AC power converter circuits are substantially equally, but oppositely offset from a nominal control angle, wherein a net current of the at least two AC power converter circuits has a greater number of component pulses than an individual AC power converter operating alone;
• and
• an interphase transformer coupling the at least two AC power converter circuits such that circulating currents between two or more positive nodes and two or more negative nodes are limited to a low percentage of maximum DC current, wherein a portion of higher order harmonics in the net current are at least partially cancelled, wherein the interphase transformer includes a first interphase transformer and a second interphase transformer, wherein each of the rectifiers in the first positive group and the second positive group is coupled in series with a separate winding of a first inter-phase transformer, and wherein each of the rectifiers in the first negative group and the second negative group is coupled in series with a separate winding of a second inter-phase transformer.