A Novel Multilevel Current-Driven Full Bridge Converter for Wide Input Voltage Range Applications
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Authors
Woelfle, Justin S.
Date
2024-01-09
Type
thesis
Language
eng
Keyword
Power converters , Power electronics , Multilevel converters , DC-DC converters
Alternative Title
Abstract
Climate change has driven the implementation of renewable energy resources, such as solar, to new heights in the past decade. Power converters utilized in solar microinverters should be highly efficient over a wide range of operating conditions. Industry-standard converters, such as the flyback converter and the LLC resonant converter, suffer in performance as the operating point deviates from the nominal design point. The deviation from the nominal operating point is caused by variations in panel manufacturing processes and changing ambient conditions, such as irradiance and temperature.
In this thesis, a novel multilevel current-driven full-bridge (MLCDFB) converter alongside a new pulse voltage modulation (PVM) scheme is proposed to address the
limitations of existing converters. The multilevel structure of the converter enables great flexibility in the operation over a wide input voltage range. The proposed converter and modulation scheme are presented and analyzed at steady state to illustrate this flexibility. Design considerations for the converter are then derived using analytical, numerical, and heuristic analysis.
Extensive experimental results are then presented to show the efficacy of the proposed converter and modulation scheme under a wide range of operating conditions. The peak efficiency of the converter is 98.01%. At the nominal input voltage, the converter achieves a CEC efficiency of 97.29%. Over an input voltage range of 34-56 V and a power of 500 W, the converter achieves efficiencies between 97.16% and 97.54%. Over the same voltage range and a power range of 300-500 W, the proposed converter efficiency varies from 97.02% to 97.91%.
Metrics to compare the proposed converter to other full-bridge-derived converters, such as the LLC converter, are then proposed. The LLC converter is chosen because
it is an industry-standard converter known for having a high efficiency. The metrics compare various loss factors, such as the RMS current, the peak current, and switching currents to the power transferred by the converter. The variation of switching frequency is also considered. These metrics describe how the losses of a converter grow as the operating point changes. An experimental comparison between the MLCDFB converter and the LLC converter is then made. The LLC converter achieves a peak efficiency of 97.60% at 500 W; however, its efficiency drastically decreases at high input voltages, down to 94.38%. This makes it clear that the proposed MLCDFB converter outperforms the LLC converter over a wide input voltage range.