A practical and cost effective wide range 6kW LLC converter for EV charging infrastructure

LLC resonant topology has been a popular choice for DC-DC conversion requirements. For the fixed output voltage applications, the LLC resonant converter is made to work near the resonant frequency to achieve the maximum efficiency. However, in applications where a wide output voltage is desired, it is difficult to tune its entire operation close to the resonant frequency, hence affecting efficiency. In this paper, a simple but unique secondary side configuration scheme has been proposed which enables the secondary winding of the LLC transformer to be used both in full bridge and center tapped configuration. This ensures that the frequency span over the entire voltage range and load is restricted, thereby increasing efficiency. Based on the proposed scheme, a 6kW LLC converter has been designed and developed, generating 200-1000V output from a nominal input of 700-800V.