Study Of The Front-ended DC/DC Converter In Grid-connected Fuel Cell Generation Power System

Green power becomes increasingly more important due to global pollution problem. Fuel cell power generation is considered the fourth-generation power plant following the thermal power generation, hydroelectric power generation, nuclear power generation, it is a new power generation mode with clean, high efficiency in 21th century. In order to efficiently utilize the energy from fuel cell, a power conditioning system (PCS) is required. A PCS generally consists of a DC/DC converter and a DC/AC inverter.The DC/DC converter for low input voltage, high power fuel cell must deal with a high voltage conversion ratio and high input current. Although many DC/DC converters have been proposed, most deal with high input voltage system that focus on step-down applications, and such converters are not suitable for a low input voltage, high power fuel cell applications. This dissertation analyzes a novel 3-phase 6-leg DC/DC converter that is used in fuel cell applications. Its converter power rating is increased by paralleling phases, the turn ratio is decreased by transformerΔ/Y connection, the size of output filter is reduced with the interleaved control, as well as reach high effiency with soft-switching technology.The dissertation studies the DC/DC convener topology that is used to increase the voltage between fuel cell output and inverter input in the grid-connected fuel cell generation power system. The basic operating principle is analyzed and discussed in detail, an averaged model is then derived, and the converter power stage circuit parameters are designed. To make the converter output voltage stable, a single voltage loop controller is designed and verified by the simulation results.As to the low frequency ripple current depression for fuel cell power system, the mechanism of ripple current propagation is analyzed in detail, the low frequency ripple current is reduced by active control with dual loop design, its theoretical basis and implementation methods are given, the effectiveness of this active control is validated by simulation. Meanwhile, the phase shift controlled converter's performance of soft-switching operation, is also analyzed in this dissertation. Finally, the main circuit components'selection, and the converter hardware design are given.