Multifunctional Onboard Charger for Electric Vehicles Integrating a Low-Voltage DC–DC Converter and Solar Roof

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A multifunctional onboard charger (OBC) is proposed that integrates the power conversion circuits for a high-voltage battery (HVB) and low-voltage battery (LVB), where the solar roof is attached to the electric vehicle (EV). Control methods are presented for systematic operation in four modes depending on the energy sources [i.e., ac grid and photovoltaics (PVs)] and batteries (i.e., HVB and LVB): grid-to-vehicle (G2V), vehicle-to-grid (V2G), HVB-to-LVB (H2L), and HVB + PV-to-LVB (HP2L). The proposed OBC reduces the dc-link capacitance by including an active power decoupling (APD) circuit in the front-end. In addition, the proposed OBC achieves a high power density and efficiency by selective operation of the topology depending on the mode. Previous studies were limited by the rated power of the low-voltage dc–dc converter (LDC), but the proposed OBC can effectively use power from the solar roof while charging the HVB and LVB simultaneously. A 3.3-kW prototype of the proposed OBC was designed, and experiments were performed to verify the waveforms and efficiency of the operating modes and control methods.