Optimizing Transformer RMS Current Using Single Phase Shift Variable Frequency Modulation for Dual Active Bridge DC-DC Converter

Abstract

The dual active bridge dc-dc converter is increasing its acceptance in various applications due to its high efficiency, high power density and the wide range of power transfer capability with galvanic isolation. All these characteristics depend on the modulation techniques used to operate the converter. In literature, suitable modulation techniques and their optimization techniques are proposed for dual active bridge dc-dc converter to improve its characteristics. However, the control parameters used in the optimized techniques reported in the literature are not decoupled. This leads to complicated control architecture and/or algorithm. This article proposes an optimization technique using single phase-shift and variable frequency modulation scheme. This is formulated with the help of the two different procedure: direct derivative and Lagrangian multiplier technique. The control parameters of the proposed optimized operation, such as phase-shift and switching frequency, are shown to be independent of each other. This helps in reducing the computational burden and increases the robustness of the controller. The proposed algorithm results in a) minimal transformer rms current, b) lower current stress on the semiconductors, c) full range of zero voltage switching operation in both the active bridges, and d) a simplified control architecture, which eliminates the current sensor for measuring the transformer current. The proposed modulation scheme is verified using simulation study as well as experimental results derived from a laboratory-scale hardware prototype.