Operating Principle and Performance Optimization of a Three-Level NPC Dual-Active-Bridge DC–DC Converter

Aiming to improve the performance features of conventional two-level dual-active-bridge (DAB) converters, this paper presents a three-level neutral-point-clamped (NPC) DAB dc-dc converter. A general modulation pattern is initially defined, the dc-link capacitor voltage balancing is analyzed in detail, and a proper balancing control is designed. Then, a set of decoupled optimization problems is formulated as a function of the available modulation degrees of freedom to minimize the predominant converter losses. Finally, a simple and practical specific modulation strategy is provided, resembling the optimum solutions. The good performance of the proposed three-level NPC DAB converter operated with the proposed modulation strategy and voltage balancing control is verified through simulation and experiments. The capacitor voltage balancing can be guaranteed for all operating conditions. In addition, it is concluded that the multilevel topology provides benefits compared with the conventional two-level DAB converter.

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