This work addresses the reliability and efficiency limits of OBCs in battery electric vehicles that arise from the use of large electrolytic capacitor banks in the DC-Link. Most practical systems adopt a two-stage architecture in which an AC–DC PFC stage is followed by an isolated DC–DC converter, with the stages coupled by an energy buffer. Electrolytic capacitors in this role suffer from reduced lifetime under thermal stress and in the presence of voltage and current ripple. The objective here is to reduce the required DC-Link capacitance enough to enable the use of film capacitors, which offer markedly longer lifetime and lower losses.

The proposed approach shifts the twice-line-frequency power component from the DC-Link into the power path: the alternating input power component of the PFC is intentionally transferred through the DC–DC stage to the HV battery. This requires synchronizing the DC–DC output current with the PFC input current so that the DC-Link stores only a minimal amount of energy. A high-efficiency CLLC resonant converter is considered for the DC–DC stage. While such converters are typically regulated for near-constant battery current, the targeted operating mode demands accurate tracking of a time-varying current reference. This imposes stringent requirements on control bandwidth, disturbance rejection, and stability across wide variations of input and battery voltage. A central premise is that stage efficiency hinges on maintaining soft switching at all times.

The paper investigates design and control measures that enable substantial DC-Link capacitance reduction and discusses the resulting trade-offs in terms of efficiency, ZVS margin, component stress, battery current ripple, and overall control robustness.