Abstract
This paper presents system-level efficiency evaluation of the suitable isolated dc/dc converters in input-series-output-parallel power electronics transformers (PET) applied for medium-voltage dc systems and provides engineering insights into the design of PETs from a system perspective. To this end, three candidates-a single-stage dual active bridge (DAB) converter, a boost converter plus a DAB with a constant boost output voltage, and a boost converter plus a DAB with a constant DAB voltage gain-are selected and evaluated from a system-level aspect. Comprehensive system-level efficiency comparisons are done with the chosen candidates, considering numbers of normal and hot standby submodules, different working conditions, rated voltages and power of the PET, switching frequencies, and commercial devices. Analysis with detailed loss breakdowns clearly shows the distribution of losses and elaborates the profound reasons behind the efficiency differences. In the comparison, the boost and DAB with a constant boost output voltage have higher or similar efficiency than the other two candidates, verified by simulation and experimental results. Considering its advantages in redundancy in the PET, the boost and DAB with constant boost output voltage are a preferable choice for submodules in input-series-output-parallel PETs.
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