EMI prediction and filter design for MHz GaN based LLC half-bridge converter

In this paper, EMI research and filter design with shielding method for a MHz switching frequency Gallium Nitride (GaN) based LLC half-bridge resonant DC-DC converter is explored. Firstly, a high-frequency model considering overall electromagnetic coupling effects for both common mode and differential mode is proposed. And EMI prediction during the frequency spectrum from 150 kHz to 30 MHz is illustrated. Then, improved inductor with shielding method is designed. According to the accurate EMI prediction and the designed inductor, high-frequency CM and DM EMI filters of the GaN based LLC converter are designed and implemented. To achieve that, different filter topologies are compared and CLC type is selected. It is confirmed that the proposed EMI filter is a convenient and cost-effective approach to suppress the EMI noise largely by both practical experiments and theoretical analysis. Moreover, to further improve the performance of the system, an optimized prototype with planar transformer is designed and implemented, which demonstrates that planar transformer can achieve smaller size, lower loss, higher power density and efficiency compared to traditional transformer.