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Technical Lecture

On-board and Off-board Charging Systems

T08.5 - Design and Control of GaN based Three-Phase / Single-Phase Combo Three-Level Flying Capacitor PFC for OBC Applications

Tuesday, March 18, 2025
9:50 AM – 10:10 AM ET
Location: Level Three, A314
As power demand for on-board chargers (OBC) is increasing to meet the fast-charging requirements, 800 V DC bus voltage is being adopted to reduce the copper losses as compared to 400 V DC bus voltage for PFC in OBCs. For higher voltage operation, multi-level converter topologies employ the benefit of reducing device stress and common-mode voltage. Hence a GaN based three-level flying capacitor converter is presented in this paper for 800 V DC bus voltage. Since flying capacitor converter has the benefit of multiplying the inductor current frequency as compared to the switching frequency thus reducing filter size, it becomes attractive for high density OBC applications. The design of the converter, specifically the GaN based flying capacitor phase leg considering symmetrical gate loop and power loop design for all the devices is discussed. It is critical to achieve symmetry in critical loops as a small asymmetry can cause unbalance in flying capacitor voltage due to small rise and fall times in GaN devices. Also, an active balancing method of flying capacitor voltage is presented to achieve robust balancing.