Optimum Hybrid Modulation for Improvement of Efficiency Over Wide Operating Range for Triple-Phase-Shift Dual-Active-Bridge Converter

Triple-phase-shift modulation of a dual-active-bridge converter allows soft switching over the complete power flow range due to additional degree of freedom control over the transformer current. Optimization of conduction angles and a phase shift between the primary and secondary bridges can allow minimized rms and peak current, which directly influence device stress and conduction and switching losses. However, the existing state of the art addresses this by using either an offline optimization-based controller or large offline data-based methods, which are expensive and require excessive resources. In this article, a piecewise model of the modulation scheme is developed, which allows analytical optimization. In addition, soft-switching conditions are included in the optimization framework allowing a complete solution, which reduces both conduction and switching losses. Finally, a hybrid controller has been proposed based on the generalized optimization results. It utilizes the optimum modulation for a given power and ensures the highest efficiency over a wide operating range. The model, the optimization framework, and the hybrid controller were developed theoretically and simulated in the MATLAB environment. A 200-W prototype was built as a proof of concept. The optimization results and the proposed controller were experimentally verified with good agreement to the theoretical analysis.