Analysis and design of power conditioning systems

A combination of high prices of fossil fuels and the increased awareness of their negative environmental impact has influenced the development of new cleaner energy sources. Among various viable technologies, fuel cells have emerged as one of the most promising sources for both portable and stationary applications. Fuel cell stacks produce DC voltage with a 2:1 variation in output voltage from no load to full load conditions. Hence, to increase the utilization efficiency and system stability, a power conditioner consisting of DC-DC and DC-AC converters is required for load interface. The design of power conditioners is driven by the application. This dissertation presents several different solutions for applications ranging from low-power portable sources for small electronics and laptop computers to megawatt-power applications for fuel cell power plants. The design and analysis for each power conditioner is presented in detail and the performance is verified using simulations and prototypes. Special consideration is given to the role of supercapacitors who act as the additional energy storage elements. It is shown that the supercapacitor connected at the terminals of a fuel cell can contribute to increased steady state stability when powering constant power loads, improved transient stability against load transients, and increased fuel efficiency (i.e. reduced hydrogen consumption).