Single/Three-Phase Compatible Sigma-Type OBC With Reduced Electrolytic Capacitor Volume

This article proposes a sigma-type dc–dc converter with a reduced energy volume of the electrolytic capacitor (E-cap) for single- and three-phase compatible on-board charger (OBC). The proposed relay box configuration uses a minimal number of relays. In single-phase grid, the E-cap is connected to the dc-link via the input-parallel output-series (IPOS) structure to absorb second harmonic current. In a three-phase grid, a film capacitor connects to the dc-link instead of E-cap, maintaining the low voltage rating of the E-cap by the input-independent output-series (IIOS) structure. Additionally, the power of the regulated converter is reduced, allowing most of the power to flow through the unregulated converter, achieving high efficiency. The proposed sigma converter achieves soft-switching under a wide voltage range and reduces the power burden of the regulated converter through a reconfigurable leg. Experimental results from an 11 kW prototype validate the proposed circuit. The converter achieved a peak efficiency of 98.12% and maintained high efficiency under a wide voltage range.