A direct AC-to-DC converter topology with high-frequency isolation

Abstract

With the increasing need for source and load isolation for safer operation, higher power density (compact size), and higher power factor requirement in the modem computer power supplies and military applications, the power converter designers have to opt for high frequency switching power supplies. Most of the above-mentioned requirements have so far been satisfied by using the conventional Switch Mode Rectifier. However, these structures still exhibit some significant disadvantages. The primary disadvantages of the conventional approach are: it requires relatively large input ac filter components, requires two stages of rectification and of de filtering (i.e., at the front-end and output rectifiers), and exhibit poor overall input power factor and current total harmonic distortion. Moreover, the input line current drawn by the front-end bridge rectifier is non sinusoidal, which can create a number of problems through the power distribution network. Combined with the increased interest in smaller size personal computers, as well as the introduction of stricter harmonic regulation, the existing approach need to be refined to yield higher power density and better input harmonic content. This thesis focuses on new topology for series resonant ac-to-dc rectifier with high frequency isolation. The proposed approach employs a PWM controlled ac controller, a series resonant tank and a high-frequency isolation transformer. With this approach, the single phase input ac is directly processed via the ac-to-ac converter eliminating the acto-dc rectification stage, power factor correction boost stage, and dc-dc converter stage present in the conventional system. The output of the high-frequency isolation transformer is rectified and processed via a filtering stage to obtain a dc output. With the addition of an input filter, the input current is near sinusoidal at unity power factor. Simulation and experimental results are presented to verify the proposed approach.