Single-stage resonant battery charger with inherent power factor correction for electric vehicles

This paper presents the study of a single-stage onboard battery charger for electric vehicle (EV) and plug-in hybrid EV (PHEV) applications. The topology had never been seen in any literature or patents but is employed in the NLG5 charger made by Brusa Elektronik AG. We thoroughly analyzed the topology and thought it would be beneficial to publish it so that advanced work can be done based on the existing structure. The charger directly transfers power from the alternating current (ac) to the battery side; thus, the bulky electrolytic capacitor in a traditional two-stage charger is eliminated. Power factor correction (PFC) is inherently achieved; thus, the control becomes very simple. In addition, all the power switches work at a zero-current switching (ZCS) condition to reduce the switching loss. The charger charges the battery with a sinusoidal-like charging current instead of a constant direct current. However, this current waveform has minimal impact on the battery life and efficiency, as demonstrated by other studies. Hence, having the advantages of high efficiency, compact size, easy control, and no need of an electrolytic capacitor, the topology is suitable for the PHEV and the pure EV onboard charging applications.