Lower-Height-Oriented Magnetic Integration Design for Onboard Power Converter of Electric Vehicles

Abstract

With the development of electric vehicles (EVs), EV onboard power converters are expected to pursue higher power density and lower height. Compared with active power devices, passive magnetics seems to be the main restriction for higher efficiency and power density. In the power distribution system, two-stage configurations of Buck+LLC converter is widely employed in various electronic equipment, which requires multiple magnetics. On this basis, the integration of two Buck+LLC converters has been studied to reduce the overall cost and improve the power density. Firstly, the two buck converters are interleaved and operate in critical mode (CRM) to reduce current ripple and realize soft switching. Hence, the two buck inductors can be negative-coupled with each other and integrated into one magnetic core to achieve lower switching frequency and smaller volume. In addition, the two LLC dc transformers are also integrated with only one switching leg and one magnetic core. By extending the effective area and canceling the high-frequency magnetic flux, the loss and volume of both the integrated buck inductors and integrated LLC transformers are reduced significantly. Detailed integration methods and parameter design processes are presented. A 700 W, 150-350 V-to-12 V dual-output dc-dc converter with 500 W/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> power density is demonstrated to verify the effectiveness and feasibility of the proposed methods.