ZVS Boundary Analysis and Optimization Strategy of Phase-Shift Values for Three-Level Dual-Active-Bridge Converters Using Harmonic Decomposition

The dual-active-bridge (DAB) converter, comprising a primary-side three-level neutral-point-clamped (NPC) bridge and a secondary-side H-bridge, represents a promising topology for voltage conversion applications between medium-voltage DC (MVDC) and low-voltage DC (LVDC). To ensure efficient operation under high-frequency conditions, it is imperative to realize a wide zero-voltage-switching (ZVS) range. In this paper, the harmonic decomposition method is utilized to analyze the ZVS boundaries and derive a universal piecewise model without complex multimodal analysis. A simple and practical ZVS optimization strategy of phase-shift values is proposed for three-level DAB converters to realize ZVS across the maximum possible θ range. It is extended further to M-level-to-N-level (ML/NL) DAB converters to become a universal method for ZVS implementation. The derived ZVS boundaries and the proposed parameter design methods are verified through simulation and experimental results.