To some extent, auto-connected transformer reduced the volume of rectifier compared with traditional isolated transformer. Meanwhile auto-connected transformer is better than traditional isolated transformer in harmonic reduction and lower load voltage ripple coefficient due to its asymmetrical structure. In terms of zigzag auto-connected transformer, to adapt to step-up occasion, traditional phase-shift angle is optimized. The effect of phase-shift angle on current and output voltage of load and on the equivalent KVA rating of autotransformer and interphase reactor are carried out. A novel phase-shift angle for zigzag auto-connected transformer is proposed to satisfy step-up voltage situation. The results of simulation suggest that equivalent KVA rating of zigzag auto-connected transformer with a novel phase-shift angle is 33% smaller than traditional isolated transformer under the same turn ratio and is more symmetrical than traditional isolated rectifier.
