The integrated LLC resonant converter using center-tapped transformer for on-board EV charger

For Electric Vehicles (EV) using on-board charger, the power density and efficiency of its charger are closely related to the technical and economical restriction of the overall system. In this paper, an integrated LLC resonant converter using center-tapped transformer is proposed to improve the power density of the EV charger. The accurate model of integrated LLC resonant converter considering leakage inductance is derived; the influences such as the change in voltage gain, the differences on resonant frequency and the lost on soft switching character which are caused by imbalance leakage inductance on two secondary windings have been discussed. The proposed tunable winding method not only shares a good balance in leakage inductor, but can also adjust the value of the leakage inductance flexibly which is practical in resonant tank design. In addition, an asymmetrical control method is also proposed to compensate the imbalance rectifying current. Finally, a 2kW on-board EV charger using integrated transformer has been made. The volume and weight of the magnetic components have been reduced by 30%, the peak overall efficiency of the EV charger can reach 95%. The degree of leakage inductance imbalance is less than 2%.