Modelling and development of fuel cell off grid power converter system

Thesis submitted in partial fulfilment of the requirements for the degree Magister Technologiae: Electrical Engineering in the Faculty of Engineering at the Cape Peninsula University of Technology 2008Fuel cell technology is an emerging technology that provides a highly efficient, quiet operation, reliable, and environmentally friendly energy conversion system for stationary, automobile (vehicle), and portable applications. An electrochemical process combines hydrogen fuel and oxygen from air to produce water, and in the process it produces electricity and heat. Fuel cell stationary applications which include residential, office buildings, hospitals, hotels, airports and others have received greater attention for their ability to utilize the heat generated for space and water heating. This combined heat and power (CHP) process increases the energy conversion efficiency greatly which in turn save cost of energy usage. Different power converter topologies for fuel cell systems residential applications are presented in this thesis for efficiency, cost, component count, input ripple current minimization technique, reliability for comparison analysis. The commercial feasibility of fuel cells rests on the cost of the fuel cell system and operating efficiency and fuel cost. The proposed power converter topology consists of two front end DC-DC converters. The first front-end DC-Dc converter is tightly controlled while the second is a full bridge four interleaved DC-DC converters. Advantages of the proposed topology are reduced input ripple current, high efficiency, low maintenance cost, smaller size, modularity, redundancy. Design overview as well as simulation results are presented. Fuel cell simulation test results, including transient response are displayed and analyzed. The concept of interleaving of multiple units of the De-De converter is proposed. Interleaving enables paralleling multiple units of the converters to achieve a high combined power. This results in using semiconductor power devices of lower current rating, lowering sizes of input and output capacitors and reducing the output ripples. Simulations results are presented that verify the concept of interleaving. Preliminary work to implement interleaving is presented, and future work is recommended