Abstract:
Under non-unity voltage gain conditions, modulating phase-shift ratios in a dual active bridge (DAB) dc-dc converter reduces reactive power and increases efficiency. Because a DAB can operate in four scenarios (forward/backward, buck/boost) with five operating modes, deriving the optimal phase-shift ratios to minimize reactive power is difficult. This paper first introduces a transformation that makes DAB operating scenarios (forward/backward, buck/boost) equivalent, then optimizes only one (forward/buck). Next, using a graphical method, this paper shows that Modes 1, 2, and 5 can be mapped into Mode 3 with lower conduction losses, and only two modes require detailed analysis. These two modes are optimized step-by-step. Under four DAB operating scenarios (forward/backward, buck/boost), global optimal phase-shift signals minimize reactive power. Global reactive-power minimization control is implemented using a simple table and control block diagram. The proposed control method outperforms other modulation schemes in experiments.
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