Global Optimization for Dual Active Bridge Converters to Minimize RMS Current

Abstract

In order to improve the steady-state performance of the dual active bridge (DAB) converter, this paper adopts the objective of minimizing the inductor root-mean-square (RMS) current to improve the converter efficiency. By elaborating an ac equivalent model, a method to simplify operation modes of the converter based on symmetric transformation is proposed, which eliminates redundant operating modes from 12 to 3. Aiming at incompletenesses of finding stationary points and Lagrange multiplier method (LMM) in minimizing the rms current, the constrained optimization problem is given, and the mathematically strict closed-form solution is derived using optimality conditions. Finally, an optimized control strategy for buck and boost operations is validated by a SiC-based small-scale prototype.