Doubly-fed Solid State Auto-Transformer (SSAT) concept for Multi-pulse Rectifiers

System size and power quality are of great concern in multi-pulse rectifiers (MPRs), especially in space critical applications. Total harmonic distortion (THD) can be reduced by phase shifting the input voltage of MPR. But low frequency transformers used for phase-shifting are bulky. While autotransformers are used in several systems when isolation is not required, they themselves can be large in high power applications. Converting the input voltage into medium frequency (MF) or high frequency (HF) and using MF/HF transformers can significantly increase the power density. However, such a MF/HF ‘solid state auto-transformer’ (SSAT) has been difficult to realize. This paper presents a new doubly-fed SSAT concept for MPRs, where half of the power passes through a diode bridge directly and the other half flows through an SST to create the phase-shift (e.g. 30° for 12-pulse rectifier) with the original voltage before passing through the diode bridge. Simulation and preliminary experimental results based on a 12-pulse rectifier topology are provided in this paper as proof of the concept. Moreover, the proposed approach is compared with relevant MPR concepts from the literature with respect to size, efficiency, and cost.