| dc.description.abstract | Recently, the demand for high-power-density converters with high efficiency and
enhanced reliability has increased considerably. To address this demand, this dissertation
introduces several low, medium, and high power converter topologies with high-frequency ac
links and soft-switching operation, both with and without galvanic isolation. These
converters can be in ac-ac, dc-ac, ac-dc, or dc-dc configurations to transfer power from the
utility, energy storage systems, or renewable/alternative energy sources (e.g., photovoltaics,
wind, and fuel cells) to stand-alone loads or the utility. The advantages of these topologies
include soft switching at turn-on and turn-off of all the semiconductor devices, exclusion of
short-life electrolytic capacitors in the link, step-up/down capability, and the use of a smallsized
high-frequency transformer for galvanic isolation. The proposed converters are also
able to generate output waveforms with arbitrary amplitude and frequency as well as
achieving a high input power factor in the ac-ac and ac-dc configurations. Moreover, some of
the introduced topologies have fault-tolerance capability, which may allow the converter to
run even with one or more faulty switches. In this case, a partial failure will not result in the
converter shutdown, and thus system availability is improved.
The high-frequency ac link of the introduced converters is composed of an ac
inductor and small ac capacitor. The link inductor is responsible for transferring power, while
the link capacitor realizes soft-switching operation. As the link components have low
reactive ratings, the converters exhibit fast dynamic responses. The inductor can be replaced
by an air-gapped high-frequency transformer to achieve galvanic isolation without the need
for any snubber circuits. Due to operation at a high frequency, the link transformer is substantially smaller in size and lower in weight compared to conventional line-frequency isolation transformers. In this work, the proposed power topologies are explained in detail, and their comprehensive analyses are given to reveal their functioning behavior in various working conditions. Simulation and experimental results at different operating points are also presented to verify the effectiveness of the introduced power converters. | en |
