Power Decoupling Control for Single-Stage On-Board Chargers

Power density and efficiency are main specifications of on-board chargers (OBC) for electric vehicles (EV). Single-stage OBCs are advantageous in terms of efficiency and cost, while the double-line frequency variation on the DC side should be carefully considered in the design phase. The double-line frequency variation may cause large charging current ripples, and subsequently, affecting the battery lifetime. Large electrolytic capacitors can be used to reduce the ripples, which makes the overall system bulky. Hence, active power decoupling (APD) technologies are favorable in single-stage OBC applications. The paper studies a control of the bidirectional buck/boost type APD circuit for a single-stage LLC-OBC. There are three control loops in the control. As the inner control loop, APD inductor current is controlled to ensure the APD working in the stable region, the second control loop is battery charging current control which is applied to control the double-line frequency part of charging current equaling to zero. The outer loop is APD capacitor voltage control which fixes the DC part of APD capacitor voltage equaling to half of battery voltage. A proportional resonant controller is applied in second loop, proportional integral controllers are used in the inner loop and the outer loop. By combining the two kinds controller, the APD control strategy can achieve power decoupling effectively in OBC applications. the paper details the design of the APD control strategy. Finally, an LLC-OBC prototype with the APD is tested to verify the efficacy of the control design.