A system efficiency improvement of DC fast-chargers in electric vehicle applications: Bypassing second-stage full-bridge DC-DC converter in high-voltage charging levels

In this paper, the DC fast charger module with its circuit topologies is studied detailed. The electric vehicle batteries are charged via DC fast chargers for quick charging. The electrical power goes through AC to DC and DC-DC power converters and reaches the battery. The first stage's responsibility is converting AC to DC, drawing low harmonic content and low reactive power from the grid, and providing fixed DC bus voltage. However, the latter task is charging the battery with a controlled current or voltage level. The common topology in the AC-DC converter is the Neutral Boost PFC in Vienna Rectifiers. However, Phase-shifted Full Bridge or LLC Resonant Converters are popular on the DC-DC side. The circuit models for those power stages are modeled in the PC platform and obtained the system efficiency of the DC Fast Charger. In the last part, the proposed idea is presented which involves sharing the charge of the electric vehicle battery between two power converters. The proposed study results show that the DC fast charging system efficiency increases remarkably on high output voltage levels.