A GaN-Based Improved Zeta Converter With Integrated Planar Transformer for 800-V Electric Vehicles

This article proposes a high-step-down dc-dc converter for electric vehicles with an 800 V battery system. The proposed converter significantly reduces the current rating requirement for the dc blocking capacitor on the secondary side by reconstructing the secondary side circuit. The maximum duty cycle of the proposed converter is larger than the phase-shift full-bridge converter, which allows the use of larger leakage inductance. This turns out to be a crucial advantage to achieve the wide range zero voltage switching (ZVS) in high switching frequencies over 500 kHz. In addition, with a three-level structure, the voltage rating of the primary side switch is determined as half the input voltage and the energy to achieve ZVS turn-on is reduced, so it is suitable for high-frequency operation using a gallium nitride (GaN) device. The two transformers are integrated with partial flux cancelation, resulting in 10.3% of power loss and 27.7% of footprint reduction. Finally, a 700 kHz GaN-based 1.2 kW prototype achieved a power density of 10.2 kW/L and a peak efficiency of 93.4%.