Loss analysis of non-isolated bidirectional DC/DC converters for hybrid energy storage system in EVs

The selection of a bidirectional non-isolated dc-dc converter interfacing the battery and ultracapacitor (UC) in electric vehicles (EVs) is of critical importance for the overall system efficiency. Generally, efficiency comparison of converters is conducted based on given fixed input and output parameters. Such a comparison may not provide fair results for EV applications since energy source voltages and traction power vary dynamically depending on the driving conditions. This paper provides a comprehensive efficiency comparison of three-level, two-level and interleaved bidirectional buck/boost converters through developed loss models considering the dynamic variables in a drive cycle. The results of the analyses show that three-level converter exhibits higher overall efficiency. A 1kW prototype has been designed and developed to serve as a proof of concept.