Unexpected bi-directional operation of Phase-Shift Full-Bridge Converter in parallel operation system

This paper discusses the effects of unexpected bi-directional operation of Phase-Shift Full-Bridge Converter in cold redundancy (CR). According to growing trends for high efficiency at light-load, cold redundancy method is strongly required in parallel operation system. However, because of unexpected backward operation, the voltage stress of primary switches is severely increased. In this paper, the period of mode change from normal operation to backward operation is investigated. The detailed operations in backward mode are described and the main factors of the severe voltage stress are analyzed. Furthermore, characteristics of switch to reduce higher voltage stress are also presented in terms of selecting switches. The validity of this study is confirmed by the experimental results of prototype 1.6kW converters.