Solid State Autotransformer (SSAT) - based Multi-pulse Rectifier Concepts for AC to DC Conversion in Space Constrained Applications
System size and power quality are of great concern in multi-pulse rectifiers (MPRs), especially in space critical applications. To improve power quality, total harmonic distortion (THD) can be reduced by phase-shifting of 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 enough in high power applications. Converting the input voltage into medium frequency (MF) or high frequency (HF) and using smaller size MF/HF transformers can significantly increase the power density. Power system of medium size aircrafts or ship does not typically need electrical isolation. These systems have the potential of saving their space in AC-DC conversion system using HF autotransformer. In this work, non-isolated solid-state autotransformer based MPR concepts will be investigated and their related issues with the design will be addressed. Taking the advantage of push-pull topology a high/medium frequency autotransformer is designed for phase-shifting required in a multi-pulse rectification system. Because of using autotransformer, system size can even be smaller than solid state transformer based MPR. Another ‘doubly-fed’ non-isolated converter is designed where half of the power is supplied directly to the diode bridge. The other half is converted to medium frequency power and then passed through HF/MF transformer for phase shifting with respect to original source. Here, the converter and HF transformer both is used only for half of the power. So, the system is smaller than SST based MPR. Analysis of efficiency, power quality, size and cost validate the potential of using these concepts in space constraint application.