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Inverter systems that feed electrical power from fuel cells into the grid must convert the direct current of the fuel cell into the alternating current of the grid. In addition, these inverters have to adapt the different voltages of the fuel-cell system and the grid to each other. In this paper, different topologies of appropriate inverter systems in the medium power range of 20 kW and higher are presented briefly. The inverter operating behavior, power rating, and efficiency are compared. The power rating and efficiency are compared using an analytical calculation of the semiconductor losses. The study includes transformerless inverters as well as two-stage inverter systems with high-frequency transformers (dc/dc converter combined with an inverter). This paper compares converter systems using insulated-gate bipolar transistors (IGBTs), e.g., a boost converter in series with a voltage-source inverter (VSI), current-source inverter, and z-source inverter or converter systems using superjunction MOSFETs, such as voltage- and current-fed full-bridge converters or a boost converter with an autotransformer. The MOSFET-based dc/dc converters must be connected in series to a VSI with IGBTs to feed into the three-phase grid. The presented converters were tested in the laboratory. Some characteristics of their laboratory performance are shown.
Date of Publication: June 2010