A soft-switch back-to-back bi-directional DC-DC converter and the FPGA based digital control design

Abstract

In this thesis, a soft switching back-to-back bi-directional DC-DC converter is proposed, and an FPGA based digital control design for it is developed.The bi-directional DC-DC converter is able to handle the power flow in both directions, either from the high voltage side to the low voltage side (step-down mode), or from the low voltage side to the high voltage side (step-up mode). Hence it can be used to transfer power between two networks which have different voltages or different functions.The proposed bi-directional converter is operated with fixed duty ratio and phase shift control. Through analysis, a simple fist-order system is obtained for the converter. Using a digital PI controller, the close loop system achieves a satisfactory dynamic performance in both step-down and step-up mode operations. A 100 W prototype converter is built, and a maximum efficiency of 92.3% is measured in the experiment.