External Magnetic Field Minimization for the Integrated Magnetics in Series Resonant Converter

The resonant dc–dc converter is preferred for high-efficiency applications due to its less switching loss and better electromagnetic interference (EMI) characteristics. However, in a wide range of steady-state voltage gain applications, such as the on-board charger application, the wide output voltage range will lead to a bulky resonant inductor, which will decrease the power density. Magnetic integration of the inductor and transformer is an effective way to reduce the total magnetic volume. However, the traditional integrated magnetics of transformer and inductor will result in high magnetic field intensity in the external space nearby the integrated magnetic component. This external magnetic field will cause large eddy current losses in the neighboring metal heatsink and serious EMI issues. In order to deal with this problem, an integrated winding structure with a negligible external magnetic field is proposed in this article. By rebuilding the external winding segments with a better coupling coefficient, the external magnetic field intensity is canceled without efficiency and size sacrifices. Detailed analysis and design procedures of the proposed structure are presented. A 6.6-kW dc–dc prototype is built to verify the cancelation effect of the magnetic field intensity in the neighboring external space.