Soft-Switching Operation With a Variable Switching Frequency Control for Switched-Quasi-Z-Source Bidirectional DC–DC Converter in EVs

Abstract

The switched-quasi-Z-source bidirectional dc–dc converter (SQBC) has the characteristics of wide voltage gain and low voltage stress, and is suitable for the power interface between the supercapacitors and the dc bus in the multisource system of electric vehicles. On the basis of the SQBC, an optimal design method for inductance parameters and variable switching frequency control strategy are proposed in this article. While remaining the wide voltage gain and low voltage stress characteristics of the topology, the soft-switching operation within the full voltage gain range is achieved without adding additional auxiliary devices. The variable switching frequency control strategy keeps the converter operating at the critical soft-switching point with the lowest switching losses per switching cycle, further improving the operation efficiency of the converter. Finally, an experimental prototype with a rated power of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i> = 300 W, input voltage of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">U</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">low</sub> = 50–150 V and output voltage of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">U</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">high</sub> = 300 V was built, and its maximum efficiency is 98.28%, which verified the correctness and effectiveness of the proposed method.