A Fault-Tolerant <i>LLC</i> Converter With High Reliability and Low Cost for Two-Stage Converters
Weikang Wang, Yang Liu, Peng Zhang, Yining Yuan, Jin Zhao, Poh Chiang Loh
Abstract
The popularity of electric vehicles is getting higher, and a large number of dc–dc converters are deployed. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> converters have witnessed a rapid deployment due to their remarkable merits, often employed as the isolation stage in two-stage converters. However, the contradiction between the increasing demand for reliability and the limited space is becoming prominent. Therefore, ensuring fault tolerance capacity with fewer devices is highly desired. A fault-tolerant <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> converter, which can keep working after multiple unexpected faults, is designed to take over half-bridge <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> converters. The prefault converter behaves like a full-bridge <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> converter and would be reconstructed to retain uninterrupted power output after faults. The reconstructed converter after the first fault behaves like two parallel half-bridge <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> converters and would be further reconstructed into a single half-bridge converter after the second fault. The faults can both be handled, including short-circuit faults and open-circuit faults. The transition processes of reconstruction are extremely short. The spike current during the transition processes is well limited, and the output voltage has a slight fluctuation. The proposed converter could drastically reduce the need for redundancy and has obvious cost advantages. Finally, a prototype is developed to verify the superiority of the proposed converter.