CLLC Modeling and Control in V2G Mode to Mitigate Double-Line Frequency Current for High-Power Density On-Board Charger

With the growth of electric vehicles (EVs), developing high-power density bidirectional on-board chargers (OBCs) has become a research hotspot. The asymmetric CLLC is one of the most promising OBC application topologies as it has no secondary-side resonant inductor compared with the symmetric CLLC, facilitating high power density and efficient design. However, when the CLLC converter operates in vehicle-to-grid (V2G) mode, it instigates a large double-line frequency (DLF) resonant current, resulting in increased power losses and deteriorating system performance. To solve these issues, a small-signal model is established for CLLC operating in the V2G mode. Using the small-signal model, the output impedance model with parasitic parameters is derived, which is not been thoroughly reported before. The developed output impedance model then assists control design by providing insights into the circuit parameter's effect. Afterward, a unique control method is proposed that incorporates a notch filter and quasi-proportional resonator (QPR) into the control loops. The proposed control method can significantly increase the CLLC closed-loop output impedance magnitude at DLF, which enables DLF resonant current reduction. Finally, a 6.6-kW OBC is built, and experiments validate that the proposed method can achieve a 40% DLF resonant current reduction in V2G mode.