Modeling and controller optimization for current-fed isolated bidirectional DC-DC converters

Current-fed isolated bidirectional DC-DC converters (CF-IBDCs) play an important role in battery energy storage systems. However, the closed-loop dynamics is rather slow with conventional proportional-integral controllers because a precise mathematic model remains absent for optimization. In this paper, a simple precise mathematical model is presented to describe the large and small-signal behaviors of the CF-IBDC. The full-order continuous model can accurately capture the dynamic behaviors and cover all operation conditions. The small-signal model is derived, and the DC filter inductors and clamp capacitors are found to be the natural causes of instability. Based on this finding, special controllers are proposed to optimize the dynamic response of the full closed-loop control system. The dynamic response time of the CF-IBDC is greatly reduced with the proposed controller. The correctness of the presented model and the dynamic response of the optimized closed-loop control system are verified by simulations.