A new DC-DC converter for fuel cell powered residential power generation systems

Abstract

This thesis presents a new topology for an isolated DC-DC converter for low voltage to high voltage conversions at high power. The proposed converter is targeted for use in fuel cell powered residential power generation systems, where low voltage to high voltage conversion at high power (>5KW) and isolation between input and output are required. Conventional DC-DC converters like forward, half bridge and full bridge for such applications need to have high turn ratio in their power transformers, to enable the high voltage boosting. This high turns ratio of the transformers results in high leakage inductance which reduces the converter's efficiency and increases the difficulty in control. The proposed converter overcomes this problem by utilizing the leakage inductance for energy conversion instead of considering it as a parasite. This reduces the problems of low efficiency and difficulty of control, caused by the leakage inductance.

The need for a separate inductor is also eliminated. Moreover the switching pattern of the FETs of the proposed converter is designed to achieve soft switching, to reduce the switching losses. Simulation results to verify the energy transfer and the closed loop performance of a 550W prototype are presented. Open loop experimental results of a 350W prototype are also presented. The concept of interleaving of multiple units of the DC-DC converter is proposed. Interleaving enables paralleling multiple units of the converter to achieve a high combined power. This results in using silicon of lower current rating, lowering the sizes of input and output capacitors and reducing the output ripple. Simulations results are presented that verify the concept of interleaving. Preliminary work to implement interleaving of two units of the proposed converter is presented, and future work is recommended.