Integrated low-voltage charging circuit with active power decoupling function for onboard battery chargers
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ORIGINAL ARTICLE
Integrated low‑voltage charging circuit with active power decoupling function for onboard battery chargers Hoang Vu Nguyen1 · Dong‑Choon Lee1 Received: 22 March 2020 / Revised: 16 June 2020 / Accepted: 18 June 2020 © The Korean Institute of Power Electronics 2020
Abstract This paper proposes a novel method to reduce the DC-link capacitor in the single-phase onboard battery chargers. A lowvoltage charging circuit is used as a two-parallel buck–boost converter to absorb ripple in the DC link. Thus, the required DC-link capacitance of the onboard battery charger can be reduced significantly without adding additional switches, heat sinks, and gated drivers. In addition, the voltage of the auxiliary capacitor can be controlled to be higher than the DC-link voltage. This allows for a further reduction of the capacitance of the auxiliary capacitor. As a result, small film capacitors can be used at the DC link instead of bulky capacitor banks or additional active power decoupling circuit. Therefore, the cost and volume of the onboard battery charger are reduced significantly. By experimental results for a 2-kW SiC-based prototype, the effectiveness of the proposed circuit has been verified. Keywords Capacitance minimization · Onboard battery charger · Single-phase converter
1 Introduction In plug-in electric vehicles (EVs), an onboard battery charger (OBC) is used to charge the high-voltage (HV) battery. Since the OBC is placed on the vehicle, high efficiency and high-power density are the main design considerations. With the development of the wide bandgap devices, the power density of the OBC can be increased since a higher switching frequency can be applied. In addition, a lower size of the passive components can be achieved. However, large capacitance banks are still required to filter out the inherent ripple power of a single-phase OBC. This is the challenge to improve power density. To reduce the DC-link capacitance banks in OBCs, several active methods have been presented [1–7]. In these works, an additional active circuit is used to transfer the power ripple to auxiliary capacitors. In [3], a buck converter is added to absorb the power ripple from the DC link. However, since the auxiliary capacitor voltage is controlled to be lower than the DC-link voltage, the reduction of the auxiliary capacitance is limited. In [5, 8], a bidirectional * Dong‑Choon Lee [email protected] 1
Department of Electrical Engineering, Yeungnam University, Gyeongsan, Korea
buck–boost converter with an auxiliary capacitor was presented, which can smoothen the DC-link voltage ripple. The auxiliary capacitor voltage can be lower or higher than the DC-link voltage, which offers the possibility to further reduce the auxiliary capacitance. However, in these active methods, additional devices are required, which leads to increases in the system complexity. In the meanwhile, with the development of EVs, the requirements in terms of high efficiency and compact design of power converters have led to research on integrated pow
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